As filed with the U.S. Securities and Exchange Commission on December 11, 2025

File No. 333-_________

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-4

REGISTRATION STATEMENT
UNDER THE SECURITIES ACT OF 1933

FIRSTSUN CAPITAL BANCORP
(Exact Name of Registrant as Specified in its Charter)

1400 16^th Street, Suite 250

Denver, Colorado 80202
(303) 831-6704

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

(Name, Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent for Service)

Copies to:

Approximate date of commencement of proposed sale of the securities to the public: As soon as practicable after this Registration Statement becomes effective and upon completion of the merger described in the enclosed proxy statement/prospectus.

If the securities being registered on this form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box: o

If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If this form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer,” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. o

If applicable, place an X in the box to designate the appropriate rule provision relied upon in conducting this transaction:

Exchange Act Rule 13e-4(i) (Cross-Border Issuer Tender Offer)            o

Exchange Act Rule 14d-1(d) (Cross-Border Third-Party Tender Offer)  o

The Registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

Information contained herein is subject to completion or amendment. A registration statement relating to the shares of FirstSun common stock to be issued in the merger has been filed with the U.S. Securities and Exchange Commission. These securities may not be sold nor may offers to buy be accepted prior to the time the registration statement becomes effective. This document shall not constitute an offer to sell or the solicitation of an offer to buy nor shall there be any sale of these securities in any jurisdiction in which such offer, solicitation or sale is not permitted or would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction.

PRELIMINARY—SUBJECT TO COMPLETION—DATED DECEMBER 11, 2025

MERGER PROPOSED—YOUR VOTE IS VERY IMPORTANT

To the Stockholders of FirstSun Capital Bancorp and First Foundation Inc.:

On October 27, 2025, FirstSun Capital Bancorp, which we refer to as “FirstSun,” and First Foundation Inc., which we refer to as “First Foundation,” entered into an Agreement and Plan of Merger, as it may be amended, modified or supplemented from time to time in accordance with its terms, which we refer to as the “merger agreement,” that provides for the combination of FirstSun and First Foundation. Following the merger, FirstSun will immediately implement a comprehensive balance sheet repositioning plan. This will involve the sale, securitization, or run-off of select First Foundation loans and a reduction in higher-cost funding sources. These steps are designed to strengthen the combined company’s capital position, enhance its credit profile, improve liquidity, and support a more diversified, relationship-focused business model. The merger and the planned balance sheet repositioning will create a premier bank in the Southwest with approximately $17 billion in assets. Under the merger agreement, First Foundation will merge with and into FirstSun, with FirstSun continuing as the surviving corporation, in a transaction we refer to as the “merger.” Immediately following the completion of the merger, First Foundation’s wholly-owned subsidiary, First Foundation Bank, a California state-chartered bank, will merge with and into FirstSun’s wholly-owned subsidiary, Sunflower Bank, National Association, a national banking association, with Sunflower Bank as the surviving bank, in a transaction we refer to as the “bank merger.”

If the merger is completed, each share of First Foundation common stock issued and outstanding immediately prior to the effective time (except for shares owned by First Foundation or FirstSun or any of their respective wholly owned subsidiaries, other than shares (i) held by First Foundation or FirstSun or any of their respective wholly owned subsidiaries in trust accounts, managed accounts, mutual funds and the like, or otherwise held in a fiduciary or agency capacity, that are beneficially owned by third parties, or (ii) held, directly or indirectly, by First Foundation or FirstSun or any of their respective wholly owned subsidiaries in respect of debts previously contracted) will be converted into the right to receive 0.16083 of a share of FirstSun common stock, plus cash in lieu of any fractional shares. Additionally, if the merger is completed, each outstanding share of First Foundation Series A Noncumulative Convertible Preferred Stock and each outstanding share of First Foundation Series C Non-Voting Common Equity Equivalent Stock (collectively the “First Foundation preferred stock”), which are currently convertible into First Foundation common stock at the rate of 1,000 shares of First Foundation common stock per share of preferred stock, will be converted into the right to receive 0.16083 of a share of FirstSun common stock, plus cash in lieu of fractional shares, for the number of shares of First Foundation common stock into which such First Foundation preferred stock were convertible immediately prior to the effective time of the merger except for (i) shares of First Foundation preferred stock owned by First Foundation or FirstSun or any of their respective wholly owned subsidiaries, in each case, other than those held in certain trust or managed accounts or in a fiduciary or agency capacity, or (ii) shares of First Foundation preferred stock held by First Foundation or FirstSun or any of their respective wholly owned subsidiaries in respect of debts previously contracted, which will be cancelled. If, as a result of the merger, a First Foundation stockholder would otherwise receive shares of FirstSun common stock that would cause the holder to own more than 4.99% of the total outstanding shares of FirstSun common stock immediately following the merger (after giving effect to the conversion of all First Foundation shares), the holder may elect instead to receive an equivalent number of shares of FirstSun non-voting common stock for the portion that would exceed the 4.99% threshold. To make this election, a First Foundation stockholder must notify FirstSun in writing of the election to receive non-voting common stock within ten business days after the effective time of the merger.

Immediately prior to the effective time of the merger, each outstanding warrant to acquire shares of First Foundation Series C Non-Voting Common Equity Equivalent Stock, with an issue date of July 8, 2024, which we refer to as First Foundation warrants, will be exercised and terminated pursuant to a Warrant Exercise and Termination Agreement, the “WETA.” All outstanding First Foundation warrants will be settled in accordance with the WETA. Immediately prior to the effective time of the merger, each holder of First Foundation warrants will automatically exercise its warrants on a cashless basis and receive First Foundation Series C Non-Voting Common Equity Equivalent Stock together with its pro rata share of an aggregate cash payment of approximately $17.5 million to all warrant holders. The total cash amount payable under the WETA is fixed and will not vary based on the market price of FirstSun common stock. The First Foundation Series C Non-Voting Common Equity Equivalent Stock received by warrant holders upon exercise will be exchanged in the merger for shares of FirstSun common stock as described in the prior paragraph.

FirstSun common stock is listed on The Nasdaq Stock Market, or Nasdaq, under the symbol “FSUN.” Following the merger, the common stock of the combined company will be listed on Nasdaq under the symbol “FSUN.” The closing price of FirstSun common stock on Nasdaq on October 27, 2025, the last trading day before public announcement of the merger, was $40.15 per share. The closing price of FirstSun common stock on Nasdaq on [·], 2025, the last practicable trading day before the printing date of this joint proxy statement/prospectus, was $[·] per share. The shares of FirstSun common stock that will be issued to First Foundation stockholders in the merger will be freely transferable, except to the extent such shares are subject to lock-up agreements entered into in connection with the merger.

First Foundation common stock is listed on the New York Stock Exchange (“NYSE”), under the symbol “FFWM.” The closing price of First Foundation common stock on NYSE on October 27, 2025, the last trading day before public announcement of the merger, was $5.55 per share. The closing price of First Foundation common stock on NYSE on [·], 2025, the last practicable trading day before the printing date of this joint proxy statement/prospectus, was $[·] per share. The implied value of the merger consideration payable for each share of First Foundation common stock based on the closing price of FirstSun common stock on October 27, 2025 and [·], 2025 is $6.46 and $[·], respectively. The value of FirstSun common stock at the time of completion of the merger could be greater than, less than or the same as the value of FirstSun common stock on the date of the accompanying joint proxy statement/prospectus or the date of your respective stockholder meeting. We urge you to obtain current market quotations for FirstSun common stock and First Foundation common stock.

Immediately following the completion of the merger, FirstSun stockholders will continue to own shares of FirstSun common stock held by the FirstSun stockholders immediately prior to the completion of the merger.

The merger will qualify as a “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended (the “Code”). Accordingly, First Foundation stockholders generally will not recognize any gain or loss for U.S. federal income tax purposes on the exchange of shares of First Foundation common stock or First Foundation preferred stock for FirstSun common stock in the merger, except with respect to any cash received by First Foundation stockholders in lieu of fractional shares of FirstSun common stock.

Based on the number of shares of First Foundation common stock outstanding as of November 30, 2025, and (i) assuming the exercise of all First Foundation warrants and the conversion of all outstanding First Foundation preferred stock into First Foundation common stock immediately prior to the effective time of the merger in accordance with their terms and (ii) the conversion of all outstanding First Foundation equity awards into awards with respect to FirstSun common stock pursuant to the merger agreement, the total number of shares of FirstSun common stock expected to be issued in connection with the merger is approximately 18,960,810 shares. For additional information, see “The Merger—Interests of First Foundation Directors and Executive Officers in the Merger.” In addition, based on (i) the number of outstanding shares of FirstSun common stock and First Foundation common stock (including shares of First Foundation preferred stock assumed to convert into FirstSun common stock and shares issuable upon settlement of unvested First Foundation equity awards) as of November 30, 2025, (ii) the exchange ratio of 0.16083, and (iii) after giving effect to the exercise, cash-out and termination of the First Foundation warrants, it is expected that legacy FirstSun stockholders will own approximately 59.5% and legacy First Foundation stockholders approximately 40.5% of the issued and outstanding shares of FirstSun common stock immediately following the merger.

FirstSun will hold a special meeting of its stockholders (which we refer to as the “FirstSun special meeting”) virtually via live webcast on [·], 2026, at [·] [a.m./p.m.] Central Time. At the FirstSun special meeting, stockholders will be asked to vote on (i) a proposal to adopt the merger agreement, and to approve the merger and the issuance of shares of FirstSun common stock in the merger for purposes of Nasdaq (which we refer to as the “FirstSun merger proposal”); (ii) a proposal to approve an amendment to FirstSun’s certificate of incorporation to increase the number of authorized shares of FirstSun’s common stock (which we refer to as the “FirstSun authorized share increase proposal”); (iii) a proposal to approve an amendment to FirstSun’s certificate of incorporation to create a class of FirstSun non-voting common stock (which we refer to as the “FirstSun non-voting common stock proposal”); and (iv) a proposal to adjourn or postpone the FirstSun special meeting, if necessary or appropriate, to solicit additional proxies in favor of any of the foregoing proposals (which we refer to as the “FirstSun adjournment proposal”).

First Foundation will hold a special meeting of its stockholders (which we refer to as the “First Foundation special meeting”) on [·], 2026, at [·] [a.m./p.m.] Pacific Time. At the First Foundation special meeting, First Foundation stockholders will be asked to consider and vote on (i) a proposal to adopt the merger agreement (which we refer to as the “First Foundation merger proposal”); (ii) a non-binding, advisory proposal to approve the compensation that may be paid or become payable to First Foundation’s named executive officers in connection with the merger, as required by Section 14A of the Securities Exchange Act of 1934 and Rule 14a-21(c) thereunder (which we refer to as the “First Foundation merger compensation proposal”); (iii) a proposal to adjourn or postpone the First Foundation special meeting, if necessary or appropriate, to solicit additional proxies in favor of the First Foundation merger proposal (which we refer to as the “First Foundation adjournment proposal”) and (iv) a proposal to approve an amendment to FirstSun’s certificate of incorporation to (1) increase the number of authorized shares of FirstSun’s common stock and (2) to create a class of FirstSun non-voting common stock (which we refer to as the “First Foundation amendment proposal”).

The merger cannot be completed unless, among other things, (i) holders of a majority of the issued and outstanding shares of FirstSun common stock vote to approve the FirstSun merger proposal, (ii) holders of a majority of FirstSun outstanding common stock entitled to vote approve the FirstSun authorized common increase proposal (iii) holders of a majority of FirstSun outstanding common stock entitled to vote approve the FirstSun non-voting common stock proposal, and (iv) holders of a majority of the issued and outstanding shares of First Foundation common stock vote to approve the First Foundation merger proposal. FirstSun and First Foundation are sending you this joint proxy statement/prospectus to ask you to vote in favor of these and other matters described in this joint proxy statement/prospectus.

YOUR VOTE IS VERY IMPORTANT, REGARDLESS OF THE NUMBER OF SHARES OF FIRSTSUN COMMON STOCK OR FIRST FOUNDATION COMMON STOCK YOU OWN. To ensure your representation at the FirstSun special meeting or First Foundation special meeting, as applicable, please complete, sign, date and return the enclosed proxy card in the enclosed postage-paid envelope or submit your proxy by telephone or via the Internet by following the instructions in the enclosed joint proxy statement/prospectus and on your proxy card. Please vote promptly whether or not you expect to attend your meeting of stockholders. Submitting a proxy now will NOT prevent you from being able to vote in person at your meeting of stockholders. If you hold your shares in “street name,” you should instruct your broker, bank or other nominee how to vote in accordance with the voting instruction form you receive from your broker, bank or other nominee.

The FirstSun board of directors has unanimously (i) determined that the merger agreement and the transactions contemplated thereby, including the merger, are advisable and in the best interests of FirstSun and its stockholders and declared the merger agreement advisable, (ii) approved the execution of the merger agreement and the consummation of the transactions contemplated thereby, including the merger and the issuance of shares of FirstSun common stock in connection with the merger, (iii) approved an amendment to FirstSun’s certificate of incorporation to increase the number of authorized shares of FirstSun common stock, and (iv) approved an amendment to FirstSun’s certificate of incorporation to create a class of FirstSun non-voting common stock, and, in each case, directed that such matters be submitted to FirstSun stockholders for consideration at the FirstSun special meeting. The FirstSun board of directors unanimously recommends that FirstSun stockholders vote “FOR” the FirstSun merger proposal, “FOR” the FirstSun authorized share increase proposal, “FOR” the FirstSun non-voting common stock proposal, and “FOR” the FirstSun adjournment proposal to adjourn the FirstSun stockholder meeting, if necessary or appropriate, to solicit additional proxies in favor of the any of the foregoing proposals.

The First Foundation board of directors has unanimously (i) determined that the merger agreement and the transactions contemplated thereby, including the merger, are advisable and in the best interests of First Foundation and its stockholders and declared the merger agreement advisable, (ii) approved the execution of the merger agreement and the consummation of the transactions contemplated thereby, including the merger, and, in each case, directed that such matters be submitted to First Foundation stockholders for consideration at the First Foundation special meeting. The First Foundation board of directors unanimously recommends that First Foundation stockholders vote “FOR” the First Foundation merger proposal, “FOR” the First Foundation merger compensation proposal, “FOR” the First Foundation adjournment proposal and “FOR” the First Foundation amendment proposal.

This joint proxy statement/prospectus provides you with detailed information about the merger agreement and the merger. It also contains or references information about FirstSun and First Foundation and certain related matters. You are encouraged to read this joint proxy statement/prospectus carefully. In particular, you should read the “Risk Factors” section beginning on page 28 for a discussion of the risks you should consider in evaluating the proposed merger and how it will affect you. You can also obtain information about FirstSun and First Foundation from documents that have been filed with the U.S. Securities and Exchange Commission that are incorporated into this joint proxy statement/prospectus by reference.

Sincerely,

Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of the merger, the issuance of shares of FirstSun common stock in connection with the merger or the other transactions described in this joint proxy statement/prospectus or passed upon the adequacy or accuracy of the disclosure in this joint proxy statement/prospectus. Any representation to the contrary is a criminal offense.

The securities to be issued in connection with the merger are not savings accounts, deposits or other obligations of any bank or savings association and are not insured by the Federal Deposit Insurance Corporation or any other governmental agency.

This joint proxy statement/prospectus is dated [·], 2025, and is first being mailed to FirstSun stockholders and First Foundation stockholders on or about [·], 2025.

NOTICE OF THE SPECIAL MEETING OF STOCKHOLDERS TO BE HELD ON [·], 2026

To the Stockholders of FirstSun Capital Bancorp:

We are pleased to invite you to attend the special meeting of stockholders, which we refer to as the FirstSun special meeting, of FirstSun Capital Bancorp, which we refer to as FirstSun, to be held on [·], 2026 at [·] [a.m./p.m.] Central Time, conducted solely by means of remote communication (virtual meeting). Instructions for accessing the virtual meeting, voting your shares electronically during the meeting and submitting questions will be provided in the accompanying joint proxy statement/prospectus and on your proxy card. At the FirstSun special meeting, FirstSun stockholders will be asked to consider and vote on the following proposals:

FirstSun will transact no other business at the FirstSun special meeting. The FirstSun board of directors has set [·], 2026 as the record date for the FirstSun special meeting. Only holders of record of FirstSun common stock at the close of business on [·], 2026 will be entitled to notice of and to vote at the FirstSun special meeting and any adjournments or postponements thereof.

Vote Required. The following votes are required to approve the proposals to be considered at the FirstSun special meeting (i) holders of a majority of the issued and outstanding shares of FirstSun common stock must vote to approve the FirstSun merger proposal; (ii) holders of a majority of the outstanding FirstSun common stock entitled to vote must vote to approve the FirstSun authorized share increase proposal; (iii) holders of a majority of the outstanding FirstSun common stock entitled to vote must vote to approve the FirstSun non-voting common stock proposal; and (iv) assuming a quorum is present, approval of the FirstSun adjournment proposal requires the affirmative vote of a majority of the votes cast on such proposal at the FirstSun special meeting.

Board Recommendation. The FirstSun board of directors has unanimously approved the merger agreement, determined that the merger agreement and the transactions contemplated thereby are advisable and in the best interests of FirstSun and its stockholders, approved the execution and delivery of the merger agreement and the consummation of the transactions contemplated thereby, including the issuance of shares of FirstSun common stock in connection with the merger, and approved the amendments to FirstSun’s certificate of incorporation described above. The FirstSun board of directors unanimously recommends that FirstSun stockholders vote “FOR” the FirstSun merger proposal, “FOR” the FirstSun authorized common increase proposal, “FOR” the FirstSun non-voting common stock proposal and “FOR” the FirstSun adjournment proposal.

YOUR VOTE IS VERY IMPORTANT, REGARDLESS OF THE NUMBER OF SHARES OF FIRSTSUN COMMON STOCK YOU OWN. Whether or not you plan to attend the FirstSun special meeting, please vote as promptly as possible by telephone, via the Internet or by completing, signing, dating and returning the enclosed proxy card in the postage-paid envelope provided. If you hold your shares in “street name” through a broker, bank or other nominee, you should direct the vote of your shares in accordance with the voting instruction form received from your broker, bank or other nominee.

If you have any questions or need assistance with voting, please contact Ed Jacques at (214) 473-7958. If you plan to attend the virtual FirstSun special meeting, please follow the instructions in the accompanying joint proxy statement/prospectus and on your proxy card for logging in, voting and submitting questions during the meeting. Stockholders holding their shares in “street name” should review the voting instructions provided by their broker, bank or other nominee regarding obtaining a control number for virtual participation.

[·], 2026
Denver, Colorado 

NOTICE OF THE SPECIAL MEETING OF STOCKHOLDERS TO BE HELD ON [·], 2026

To the Stockholders of First Foundation Inc.:

We are pleased to invite you to attend the special meeting of stockholders, which we refer to as the First Foundation special meeting, of First Foundation Inc., which we refer to as First Foundation, to be held on [·], 2026 at [·] at [·] [a.m./p.m.] Pacific Time. Instructions for accessing the virtual meeting, voting your shares electronically during the meeting and submitting questions will be provided in the accompanying joint proxy statement/prospectus and on your proxy card. At the First Foundation special meeting, First Foundation stockholders will be asked to consider and vote on the following proposals:

The First Foundation board of directors has set [·], 2026 as the record date for the First Foundation special meeting. Only holders of record of First Foundation common stock at the close of business on [·], 2026 will be entitled to notice of and to vote at the First Foundation special meeting and any adjournments or postponements thereof.

Vote Required. The affirmative vote of a majority of the issued and outstanding shares of First Foundation common stock entitled to vote thereon is required to approve the First Foundation merger proposal. The approval of the First Foundation adjournment proposal, the First Foundation merger compensation proposal, and the First Foundation amendment proposal each requires the affirmative vote of holders of a majority voting power entitled to vote thereon, present in person or represented by proxy, at the First Foundation special meeting.

The votes on the First Foundation merger compensation proposal and the First Foundation amendment proposal are separate from the votes on the other proposals at the First Foundation special meeting. Because these votes are advisory only, their outcomes will not be binding on First Foundation, FirstSun or the combined company. Accordingly, merger-related compensation will be paid to First Foundation’s named executive officers in accordance with their existing agreements and arrangements, even if stockholders do not approve the First Foundation merger compensation proposal. Likewise, while First Foundation is seeking stockholder support for the First Foundation amendment proposal—and believes such support is appropriate given that many First Foundation stockholders will become FirstSun stockholders after the merger—the outcome of this vote will also not be binding.

First Foundation will transact no other business at the First Foundation special meeting.

Board Recommendation. The First Foundation board of directors has unanimously approved the merger agreement, determined that the merger agreement and the transactions contemplated thereby are advisable and in the best interests of First Foundation and its stockholders, approved the execution and delivery of the merger agreement and the consummation of the transactions contemplated thereby. The First Foundation board of directors unanimously recommends that First Foundation stockholders vote “FOR” the First Foundation merger proposal, “FOR” the First Foundation merger compensation proposal, “FOR” the First Foundation adjournment proposal and “FOR” the First Foundation amendment proposal.

YOUR VOTE IS VERY IMPORTANT, REGARDLESS OF THE NUMBER OF SHARES OF FIRST FOUNDATION COMMON STOCK YOU OWN. Whether or not you plan to attend the First Foundation special meeting, please vote as promptly as possible by telephone, via the Internet or by completing, signing, dating and returning the enclosed proxy card in the postage-paid envelope provided. If you hold your shares in “street name” through a broker, bank or other nominee, you should direct the vote of your shares in accordance with the voting instruction form received from your broker, bank or other nominee.

If you have any questions or need assistance with voting, please contact [·] at [·].

[·], 2026
Irving, Texas

ABOUT THIS JOINT PROXY STATEMENT/PROSPECTUS

This joint proxy statement/prospectus forms part of a Registration Statement on Form S-4 filed with the U.S. Securities and Exchange Commission (“SEC”) by FirstSun. It constitutes a prospectus of FirstSun under Section 5 of the Securities Act of 1933, as amended (the “Securities Act”), with respect to the shares of FirstSun common stock to be issued to First Foundation stockholders in connection with the merger. It also serves as a joint proxy statement for both FirstSun and First Foundation and is being used by each of their respective boards of directors to solicit proxies from their stockholders in connection with the approval of the merger and related matters.

All references in this joint proxy statement/prospectus to “FirstSun” refer to FirstSun Capital Bancorp, a Delaware corporation, and all references to “Sunflower Bank” refer to Sunflower Bank, National Association, a national banking association.

All references in this joint proxy statement/prospectus to “First Foundation” refer to First Foundation Inc., a Delaware corporation, and all references to “First Foundation Bank” refer to First Foundation Bank, a California state-chartered bank.

All references in this joint proxy statement/prospectus to the “combined company” refer to FirstSun immediately following completion of the merger.

Unless otherwise indicated or the context otherwise requires:

All references in this joint proxy statement/prospectus to the “merger agreement” refer to the Agreement and Plan of Merger dated October 27, 2025, by and between FirstSun and First Foundation.

All references in this joint proxy statement/prospectus to “we,” “our” and “us” refer to FirstSun and First Foundation collectively, unless otherwise indicated or as the context requires.

You should rely only on the information contained in, attached to, or incorporated by reference in the accompanying joint proxy statement/prospectus. No person has been authorized to give any information or make any representation about the merger, FirstSun, or First Foundation that is different from or adds to the information in this joint proxy statement/prospectus or in documents that are publicly filed with the SEC. We take no responsibility for, and provide no assurance as to the reliability of, any other information that others may give you. You should not assume that the information contained in this joint proxy statement/prospectus is accurate as of any date other than the date of this joint proxy statement/prospectus, and neither the mailing of this joint proxy statement/prospectus to FirstSun or First Foundation stockholders nor the issuance of FirstSun common stock in the merger will create any implication to the contrary.

This joint proxy statement/prospectus does not constitute an offer to sell, or a solicitation of an offer to buy, any securities, or the solicitation of a proxy, in any jurisdiction in which or from any person to whom it is unlawful to make any such offer or solicitation in such jurisdiction.

WHERE YOU CAN FIND MORE INFORMATION

Both FirstSun and First Foundation file annual, quarterly and current reports, proxy statements and other business and financial information with the SEC. In addition, FirstSun and First Foundation file reports and other business and financial information with the SEC electronically, and the SEC maintains a website located at www.sec.gov containing this information. You will also be able to obtain these documents, free of charge, from FirstSun at https://ir.firstsuncb.com/investor-relations/default.aspx under the tab “Financials” and then click the link for “SEC Filings”, or from First Foundation at https://investor.ff-inc.com/investor-home/default.aspx under the tab “Financials” and then click the link for SEC filings.

FirstSun has filed a registration statement on Form S-4 of which this joint proxy statement/prospectus forms a part. As permitted by SEC rules, this joint proxy statement/prospectus does not contain all of the information included in the registration statement or in the exhibits or schedules to the registration statement. You may obtain a free copy of the registration statement, including any amendments, schedules and exhibits at the addresses set forth below. Statements contained in this joint proxy statement/prospectus as to the contents of any contract or other documents referred to in this joint proxy statement/prospectus are not necessarily complete. In each case, you should refer to the copy of the applicable contract or other document filed as an exhibit to the registration statement. This joint proxy statement/prospectus incorporates by reference documents that FirstSun and First Foundation have previously filed with the SEC. These documents contain important information about the companies and their financial condition. See “Incorporation of Certain Documents by Reference” beginning on page 180. These documents are available without charge to you upon written or oral request to the applicable company’s principal executive offices. The respective addresses and telephone numbers of such principal executive offices are listed below.

If you are a FirstSun stockholder and have any questions regarding the accompanying joint proxy statement/prospectus or the FirstSun special meeting, you may contact Ed Jacques, Director of Investor Relations and Business Development, at (214) 473-7958.

If you are a First Foundation stockholder and have any questions regarding the accompanying joint proxy statement/prospectus or the First Foundation special meeting, you may contact First Foundation’s proxy solicitor, [·], by calling toll-free at [·] or by email at [·].

To obtain timely delivery of these documents, you must request them no later than five business days before the date of each of the stockholder meetings. This means that, to ensure timely delivery, you should request the information no later than [·], 2026, for the FirstSun stockholder meeting and no later than [·], 2026, for the First Foundation stockholder meeting.

MARKET AND INDUSTRY DATA

This joint proxy statement/prospectus includes government, industry, and trade association data, forecasts, and other information that FirstSun and First Foundation have prepared, in part based on data, forecasts, and information obtained from independent trade associations, industry publications and surveys, government agencies, and other publicly available sources, which may relate to particular markets or geographic regions. Statements regarding market position are based on market data currently available to FirstSun and First Foundation. Industry publications, surveys, and forecasts generally state that the information contained therein has been obtained from sources believed to be reliable. Although FirstSun and First Foundation believe these sources are reliable, neither FirstSun nor First Foundation has independently verified such information.

Some data is also based on FirstSun’s and First Foundation’s good-faith estimates, derived from management’s knowledge of their respective industries and independent sources. FirstSun and First Foundation believe their internal research is reliable, even though it has not been verified by any independent sources. While neither FirstSun nor First Foundation is aware of any misstatements regarding the industry data presented herein, their estimates involve risks and uncertainties and are subject to change based on various factors, including those discussed under “Risk Factors” in this joint proxy statement/prospectus. Forward-looking information obtained from these sources is subject to the same qualifications and additional uncertainties applicable to other forward-looking statements in this joint proxy statement/prospectus. 

IMPLICATIONS OF BEING AN EMERGING GROWTH COMPANY

As a company with less than $1.235 billion in total annual gross revenue during its last fiscal year, FirstSun qualifies as an “emerging growth company” under the Jumpstart Our Business Startups Act of 2012, or the JOBS Act. An emerging growth company may take advantage of reduced reporting requirements and is relieved of certain other significant requirements that are otherwise generally applicable to public companies. As an emerging growth company:

FirstSun expects to remain an emerging growth company through December 31, 2025, and may continue to take advantage of some or all of these provisions until that time or until it otherwise ceases to qualify as an emerging growth company. FirstSun will cease to qualify as an emerging growth company if it has more than $1.235 billion in total annual gross revenue, if it issues more than $1.0 billion of non-convertible debt in a three-year period, or if it is deemed to be a large accelerated filer—meaning the market value of its common stock held by non-affiliates exceeds $700.0 million as of any June 30—in which case FirstSun would no longer be an emerging growth company as of the following December 31.

Accordingly, certain of the reduced reporting and other requirements described above will apply to this joint proxy statement/prospectus and to FirstSun’s periodic reports filed with the SEC through 2025 but will not apply to future filings once FirstSun ceases to qualify as an emerging growth company.

TABLE OF CONTENTS

QUESTIONS AND ANSWERS

The following are brief answers to certain questions that you may have regarding the merger between FirstSun Capital Bancorp (“FirstSun”) and First Foundation Inc. (“First Foundation”) and the meetings of the stockholders of FirstSun and First Foundation and the other matters being proposed for consideration at those meetings. We urge you to read this section carefully, as well as the entirety of this joint proxy statement/prospectus, including all annexes and exhibits, because the information in this section may not provide all the information that might be important to you in determining how to vote regarding the merger and the other matters being proposed for consideration at the FirstSun and First Foundation stockholder meetings. Additional important information is also contained in the annexes to, and the documents incorporated by reference in, this joint proxy statement/prospectus. See “Where You Can Find More Information” on page iii.

Q: WHAT IS THE MERGER?

A: FirstSun and First Foundation entered into an Agreement and Plan of Merger, dated October 27, 2025 (the “merger agreement”). Under the merger agreement, First Foundation will merge with and into FirstSun, with FirstSun continuing as the surviving corporation (the “merger”). Immediately following the merger, or at such later time as the parties may mutually agree, First Foundation Bank, a California state-chartered bank and wholly owned subsidiary of First Foundation, will merge with and into Sunflower Bank, National Association, a national banking association and wholly owned subsidiary of FirstSun, with Sunflower Bank continuing as the surviving bank (the “bank merger”).

To complete the merger, each company must obtain the requisite stockholder approvals. Accordingly, FirstSun will hold a special meeting of its stockholders (the “FirstSun special meeting”), and First Foundation will hold a special meeting of its stockholders (the “First Foundation special meeting”). This joint proxy statement/prospectus is being furnished to you in connection with those meetings. A copy of the merger agreement is attached as Annex A to this joint proxy statement/prospectus. We urge you to read this joint proxy statement/prospectus and the merger agreement carefully and in their entirety before voting.

Q: WHY AM I RECEIVING THIS DOCUMENT?

A: To complete the merger, among other things:

Each of FirstSun and First Foundation is providing this joint proxy statement/prospectus to its stockholders to assist them in deciding how to vote their shares of common stock on the matters to be considered at their respective special meetings.

This document serves as both a joint proxy statement of FirstSun and First Foundation and a prospectus of FirstSun. It is a joint proxy statement because the boards of directors of both companies are soliciting proxies from their stockholders using this document. It is a prospectus because, in connection with the merger, FirstSun will issue shares of FirstSun common stock to First Foundation common stockholders and to holders of First Foundation preferred stock upon conversion of such preferred stock in the merger, as described herein.

Q: WHAT WILL FIRST FOUNDATION COMMON STOCKHOLDERS RECEIVE IN THE MERGER?

A: If the merger is completed, each share of First Foundation common stock outstanding immediately prior to the effective time of the merger (except for shares owned by First Foundation or FirstSun or any of their respective wholly owned subsidiaries, other than shares (i) held by First Foundation or FirstSun or any of their respective wholly owned subsidiaries in trust accounts, managed accounts, mutual funds and the like, or otherwise held in a fiduciary or agency capacity, that are beneficially owned by third parties, or (ii) held, directly or indirectly, by First Foundation or FirstSun or any of their respective wholly owned subsidiaries in respect of debts previously contracted, which shares will be cancelled) will be converted into the right to receive 0.16083 of a share of FirstSun common stock, which we refer to as the exchange ratio.

FirstSun will not issue fractional shares of FirstSun common stock in the merger. Instead, any First Foundation stockholder entitled to a fractional share will receive a cash payment (rounded to the nearest cent) equal to: (i) the fraction of a share (rounded to the nearest thousandth) of FirstSun common stock to which such stockholder would otherwise be entitled, multiplied by (ii) the average of the closing-sale prices of FirstSun common stock on Nasdaq for the five full trading days ending on the trading day immediately preceding the closing date of the merger. The FirstSun common stock received in the merger will have the rights described under “Description of Capital Stock of the Combined Company” in this joint proxy statement/prospectus.

Q: WHAT WILL FIRST FOUNDATION PREFERRED STOCKHOLDERS RECEIVE IN THE MERGER?

A: First Foundation has two outstanding classes of preferred stock: (1) its Series A Noncumulative Convertible Preferred Stock (“Series A stock”) and (2) its Series C Non-Voting Common Equity Equivalent Stock (“Series C stock”). At the effective time of the merger, each share of Series A stock and each share of Series C stock issued and outstanding immediately prior to the effective time of the merger will automatically convert into the right to receive a number of shares of FirstSun common stock equal to (i) the number of shares of First Foundation common stock that such share was convertible into immediately prior to the effective time of the merger, multiplied by (ii) the exchange ratio. Any fractional shares resulting from this conversion will be paid in cash, without interest, as described in this joint proxy statement/prospectus.

Q: WHAT WILL HAPPEN TO FIRST FOUNDATION WARRANTS IN THE MERGER?

A: Immediately prior to the effective time of the merger, each outstanding warrant to acquire shares of First Foundation Series C stock, issued on July 8, 2024 (the “First Foundation warrants”), will be exercised and terminated pursuant to a Warrant Exercise and Termination Agreement (the “WETA”). All outstanding First Foundation warrants will be settled in accordance with the WETA. Under the WETA, each holder of First Foundation warrants will automatically exercise its warrants on a cashless basis and receive shares of Series C stock together with its pro rata share of an aggregate cash payment of approximately $17.5 million to all warrant holders, without interest. The total cash amount payable under the WETA is fixed and will not vary based on the market price of FirstSun common stock. The Series C shares received upon exercise will be exchanged in the merger for shares of FirstSun common stock as described under “The Merger—Merger Consideration” in this joint proxy statement/prospectus.

Q: WHAT PERCENTAGE OF THE COMBINED COMPANY WILL FIRST FOUNDATION STOCKHOLDERS OWN?

A: Based on (i) the number of outstanding shares of FirstSun common stock and First Foundation common stock (including shares of First Foundation preferred stock assumed to convert into FirstSun common stock and shares issuable upon settlement of unvested First Foundation equity awards) as of November 30, 2025, (ii) the exchange ratio of 0.16083, and (iii) after giving effect to the exercise, termination and cash-out of the First Foundation warrants, it is expected that legacy FirstSun stockholders will own approximately 59.5% and legacy First Foundation stockholders will own approximately 40.5% of the issued and outstanding shares of FirstSun common stock immediately following the merger. The actual percentage will depend on the number of shares of First Foundation common stock and preferred stock outstanding immediately prior to the effective time of the merger.

Q: ARE THERE ANY RISKS I SHOULD CONSIDER IN DECIDING HOW TO VOTE?

A: Yes. You should carefully read and consider the risk factors described in the section entitled “Risk Factors” beginning on page 28 of this joint proxy statement/prospectus. You should also review the risk factors described in the documents incorporated by reference into this joint proxy statement/prospectus, including those contained in FirstSun’s and First Foundation’s periodic reports filed with the SEC. We urge you to read this entire joint proxy statement/prospectus, including all annexes and exhibits, carefully and in its entirety before making any voting decision.

Q: HOW MAY I ELECT TO RECEIVE FIRSTSUN NON-VOTING COMMON STOCK IN THE MERGER?

A: If, as a result of the merger, you would own more than 4.99% of the outstanding shares of FirstSun common stock, you may elect to receive FirstSun non-voting common stock instead of FirstSun voting common stock for the portion of your shares that would exceed that ownership limit. You may make this election by checking the appropriate box on the letter of transmittal or other election form provided to you by FirstSun. If you select this option, you will receive FirstSun non-voting common stock only for the excess shares above the 4.99% threshold; if you would not exceed that limit, your election will have no effect and you will receive only FirstSun voting common stock in the merger. If you do not make this election on your letter of transmittal or other election form provided to you by FirstSun, you may still elect to receive FirstSun non-voting common stock for any excess shares by providing written notice to FirstSun no later than ten business days after the effective time of the merger. Such notice should be directed to Kelly Rackley at Kelly.Rackley@sunflowerbank.com. FirstSun non-voting common stock will have the same economic rights as FirstSun voting common stock, except that it will not carry voting rights.

Q: HOW WILL THE MERGER AFFECT FIRST FOUNDATION EQUITY AWARDS?

A: At the effective time of the merger, all outstanding First Foundation equity awards will be assumed by FirstSun and converted into corresponding awards covering shares of FirstSun common stock, with the number of shares adjusted based on the exchange ratio and rounded to the nearest whole share.

Q: HOW WILL THE MERGER AFFECT FIRST FOUNDATION’S 401(K) PLAN?

A: The merger agreement provides that, if requested by FirstSun, First Foundation will terminate its 401(k) plan effective immediately prior to the closing, subject to the merger being completed. Following the merger, continuing employees will be eligible to participate in a 401(k) plan sponsored by FirstSun or one of its subsidiaries without a gap in participation and will be permitted to roll over eligible distributions from the First Foundation 401(k) plan to the FirstSun 401(k) plan, including outstanding plan loans, subject to applicable law and the terms of the FirstSun plan.

Q: WILL THE VALUE OF THE MERGER CONSIDERATION TO FIRST FOUNDATION STOCKHOLDERS CHANGE BETWEEN THE DATE OF THIS JOINT PROXY STATEMENT/PROSPECTUS AND THE TIME THE MERGER IS COMPLETED?

A: Yes. Although the exchange ratio is fixed, the value of the merger consideration is dependent upon the market value of FirstSun common stock and therefore will fluctuate with the market price of FirstSun common stock. Accordingly, any change in the market price of FirstSun common stock prior to the merger will affect the market value of the merger consideration that First Foundation stockholders will receive in the merger.

Q: WHAT WILL HAPPEN TO SHARES OF FIRSTSUN COMMON STOCK IN THE MERGER?

A: Nothing. Each share of FirstSun common stock outstanding immediately prior to the effective time of the merger will remain outstanding as a share of FirstSun common stock following the merger.

Q: WHAT AM I BEING ASKED TO VOTE ON?

A: FirstSun Special Meeting: FirstSun stockholders are being asked to consider and vote on the following proposals:

First Foundation Special Meeting: First Foundation stockholders are being asked to consider and vote on the following proposals:

Q: WHY ARE FIRST FOUNDATION STOCKHOLDERS BEING ASKED TO CONSIDER AND VOTE ON THE FIRST FOUNDATION MERGER COMPENSATION PROPOSAL?

A: Under SEC rules, First Foundation is required to seek a non-binding, advisory vote with respect to the compensation that may be paid or become payable to First Foundation’s named executive officers that is based on or otherwise relates to the merger, or “golden parachute” compensation.

Q: WHAT HAPPENS IF HOLDERS OF FIRST FOUNDATION COMMON STOCK DO NOT APPROVE, BY NON-BINDING, ADVISORY VOTE, THE FIRST FOUNDATION MERGER COMPENSATION PROPOSAL?

A: The vote on the proposal to approve the merger-related compensation arrangements for each of First Foundation’s named executive officers is separate and apart from the votes to approve the other proposals being presented at the First Foundation special meeting. Because the vote on the proposal to approve the First Foundation merger compensation proposal is advisory in nature only, it will not be binding upon First Foundation, FirstSun or the combined company in the merger. Accordingly, the merger-related compensation will be paid to First Foundation’s named executive officers to the extent payable in accordance with the terms of their compensation agreements and arrangements, even if the holders of First Foundation common stock do not approve the First Foundation merger compensation proposal.

Q: WHY ARE FIRST FOUNDATION STOCKHOLDERS BEING ASKED TO CONSIDER AND VOTE ON THE FIRST FOUNDATION AMENDMENT PROPOSAL?

A: First Foundation is asking its stockholders to approve, at the First Foundation special meeting, an amendment to the FirstSun certificate of incorporation (1) to increase the number of authorized shares of FirstSun common stock and (2) to create a class of FirstSun non-voting common stock. Following completion of the merger, First Foundation stockholders who receive the stock consideration will be receiving FirstSun common stock governed by the FirstSun certificate of incorporation. Accordingly, First Foundation stockholders are being provided the opportunity to cast an advisory vote on the First Foundation amendment proposal.

Q: WHAT HAPPENS IF HOLDERS OF FIRST FOUNDATION COMMON STOCK DO NOT APPROVE, BY NON-BINDING, ADVISORY VOTE, THE FIRST FOUNDATION AMENDMENT PROPOSAL?

A: As an advisory vote, this proposal is not binding upon FirstSun or the FirstSun board, and approval by First Foundation stockholders of this proposal is not a condition to completion of the merger. However, First Foundation seeks the support of First Foundation stockholders and believes that stockholder support is appropriate because many First Foundation stockholders will become FirstSun stockholders upon completion of the merger. Accordingly, holders of First Foundation common stock are being provided the opportunity to cast an advisory vote on the First Foundation amendment proposal.

Q: WHEN AND WHERE ARE THE FIRSTSUN SPECIAL MEETING AND FIRST FOUNDATION SPECIAL MEETING?

A: FirstSun special meeting: The FirstSun special meeting will be held on [·], 2026, at [·] [a.m./p.m.] Central Time and will be conducted solely by means of remote communication (virtual meeting). Instructions for accessing the virtual meeting and voting electronically will be provided in the accompanying joint proxy statement/prospectus and on your proxy card.

First Foundation special meeting: The First Foundation special meeting will be held on [·], 2026, at [·] at [·] [a.m./p.m.] Pacific Time.

Q: HOW DO I VIRTUALLY ATTEND AND PARTICIPATE IN THE FIRSTSUN SPECIAL MEETING?

A: The FirstSun special meeting will be conducted solely by means of remote communication (a virtual meeting). The webcast will begin promptly at [·] [a.m./p.m.] Central Time on [·], 2026. You are encouraged to log in prior to the start time to allow for check-in and technical setup. Online check-in will open at [·] [a.m./p.m.] Central Time.

To attend the virtual meeting, vote, and submit questions during the meeting, please go to: [·] and enter the control number printed on your Notice of Internet Availability, proxy card, or voting instruction form.

During the virtual meeting, you will be able to:

Questions may be submitted before or during the meeting through the virtual meeting website. Similar questions may be grouped and answered together, subject to time constraints.

If you experience technical difficulties accessing the meeting, technical support information will be available on the meeting website.

Q: WHO IS ENTITLED TO VOTE AT EACH MEETING?

A: FirstSun special meeting: All holders of FirstSun common stock who held shares at the close of business on [·], 2026, which we refer to as the FirstSun record date, are entitled to receive notice of and to vote at the FirstSun special meeting, provided that such shares of FirstSun common stock remain outstanding on the date of the FirstSun special meeting.

First Foundation special meeting: All holders of First Foundation common stock who held shares at the close of business on [·], 2026, which we refer to as the First Foundation record date, are entitled to receive notice of and to vote at the First Foundation special meeting, provided that such shares of First Foundation common stock remain outstanding on the date of the First Foundation special meeting.

Q: WILL HOLDERS OF FIRST FOUNDATION PREFERRED STOCK BE ENTITLED TO VOTE ON THE MERGER AT THE FIRST FOUNDATION SPECIAL MEETING?

A: No. Holders of First Foundation preferred stock, including holders of Series A stock and Series C stock, are not entitled to vote at the First Foundation special meeting. These classes of preferred stock do not have voting rights with respect to the proposals to be considered at the First Foundation special meeting. Holders of First Foundation preferred stock should not submit a proxy card with respect to the First Foundation special meeting and should not attempt to vote their preferred shares at the meeting.

Q: ARE THERE VOTING AGREEMENTS WITH THE COMPANIES’ DIRECTORS OR STOCKHOLDERS?

A: Yes. Each member of the First Foundation board of directors who holds shares of First Foundation common stock and certain other First Foundation stockholders entered into a support agreement with FirstSun. Under these agreements, each such stockholder agreed, subject to the terms of the agreement, to vote all of his or her shares in favor of the adoption of the merger agreement and against any alternative acquisition proposal. As of the record date, approximately [·]% of the outstanding shares of First Foundation common stock are subject to these support agreements.

In addition, each member of the FirstSun board of directors who holds shares of FirstSun common stock and certain other FirstSun stockholders entered into a support agreement with First Foundation. Under these agreements, each such stockholder agreed, subject to the terms of the agreement, to vote all of his or her shares of FirstSun common stock in favor of the approval of the merger agreement and the transactions contemplated by it, including the merger. As of the record date, approximately [·]% of the outstanding shares of FirstSun common stock are subject to these support agreements.

Q: WHAT HAPPENS IF I SELL MY SHARES AFTER THE APPLICABLE RECORD DATE BUT BEFORE MY COMPANY’S SPECIAL MEETING?

A: Each of the FirstSun record date and the First Foundation record date will be earlier than the date of their respective special meetings and earlier than the date that the merger is expected to be completed. If you sell or otherwise transfer your shares of FirstSun common stock after the FirstSun record date but before the date of the FirstSun special meeting, you will retain your right to vote at the FirstSun special meeting (provided that such shares remain outstanding on the date of the FirstSun special meeting), but you will not have the right to receive any merger consideration with respect to those shares because FirstSun shares will remain outstanding and are not being exchanged in the merger.

If you sell or otherwise transfer your shares of First Foundation common stock after the First Foundation record date but before the completion of the merger, you will retain your right to vote at the First Foundation special meeting (provided that such shares remain outstanding on the date of the First Foundation special meeting), but you will not have the right to receive the merger consideration to be received by First Foundation stockholders in the merger. To receive the merger consideration, you must hold your shares of First Foundation common stock through completion of the merger.

Q: WHAT DO I NEED TO DO NOW?

A: After carefully reading and considering the information contained in or incorporated by reference into this joint proxy statement/prospectus, including its annexes, please vote your shares as soon as possible, so that your shares will be represented at your respective company’s special meeting. Please follow the instructions set forth herein or on the enclosed proxy card or on the voting instruction form provided by your bank, broker or other nominee if your shares are held in “street name.”

Q: HOW DO I VOTE?

A: If you are a stockholder of record of FirstSun as of the record date for the FirstSun special meeting, you may submit your proxy before the FirstSun special meeting (which will be conducted solely by means of remote communication) in any of the following ways:

If you are a stockholder of record of First Foundation as of the record date for the First Foundation special meeting, you may submit your proxy before the First Foundation special meeting (which will be conducted solely by means of remote communication) in any of the following ways:

If you hold your shares in “street name” through a bank, broker or other nominee, you must follow the voting instructions provided by that bank, broker or other nominee. You may not vote shares held in “street name” directly at the special meetings unless you obtain a legal proxy from the record holder.

Q: WHAT CONSTITUTES A QUORUM AT EACH MEETING?

A: FirstSun Special Meeting: The presence, in person or represented by proxy, of at least a majority of the total number of outstanding shares of FirstSun common stock entitled to vote will constitute a quorum for the FirstSun special meeting. Abstentions will be counted for purposes of determining the presence of a quorum, but broker non-votes will not be counted for purposes of determining whether a quorum exists.

First Foundation Special Meeting: The presence, in person or represented by proxy, of holders of a majority of the voting power entitled to vote at the meeting constitutes a quorum for the First Foundation special meeting. Abstentions and broker non-votes will be included in determining the number of shares present for purposes of determining the presence of a quorum.

Q: WHAT VOTE IS REQUIRED TO APPROVE EACH PROPOSAL AT THE FIRSTSUN SPECIAL MEETING?

A: For the FirstSun merger proposal:

For the FirstSun authorized common increase proposal:

For the FirstSun non-voting common stock proposal:

FirstSun adjournment proposal:

Q: WHAT VOTE IS REQUIRED TO APPROVE EACH PROPOSAL AT THE FIRST FOUNDATION SPECIAL MEETING?

A: For the First Foundation merger proposal:

First Foundation merger compensation proposal:

First Foundation adjournment proposal:

First Foundation amendment proposal:

Q: IF MY SHARES ARE HELD IN “STREET NAME,” WILL MY BROKER VOTE MY SHARES FOR ME?

A: No. Under the rules of the applicable listing exchange, banks, brokers and other nominees who hold shares in “street name” do not have discretionary authority to vote on any of the proposals to be presented at the FirstSun special meeting or the First Foundation special meeting without instruction from the beneficial owner. Because all proposals to be voted on at the FirstSun special meeting and the First Foundation special meeting are considered “non-routine” matters, no broker discretionary voting is permitted. As a result, if you hold your shares in “street name,” your shares will not be voted unless you instruct your bank, broker or other nominee how to vote. It is therefore critical that you provide voting instructions.

Q: WHY IS MY VOTE IMPORTANT?

A: The approval of the merger requires the affirmative vote of both First Foundation stockholders and FirstSun stockholders. If you do not vote, it will be more difficult to obtain the necessary quorum and stockholder approvals for the merger to be completed. For First Foundation stockholders, failure to vote, an abstention, or failure to instruct your bank, broker, or other nominee how to vote will have the same effect as a vote “AGAINST” the First Foundation merger proposal. For FirstSun stockholders, failure to vote, an abstention, or failure to instruct your bank, broker, or other nominee how to vote will have the same effect as a vote “AGAINST” the FirstSun merger proposal, the FirstSun authorized common increase proposal, and the FirstSun non-voting common stock proposal.

Q: WILL THE MERGER PROPOSAL STILL BE SUBMITTED TO STOCKHOLDERS IF EITHER BOARD CHANGES ITS RECOMMENDATION?

A: Yes. Unless the merger agreement is terminated, both First Foundation and FirstSun are required to convene their respective stockholder meetings and submit the merger agreement and related proposals to a vote of their stockholders—even if either the First Foundation board of directors or the FirstSun board of directors withdraws, modifies, or qualifies its recommendation.

Under the merger agreement, each board of directors may, in limited circumstances and subject to compliance with the merger agreement’s notice and negotiation obligations, change its recommendation if it receives a superior proposal and, after consulting with its financial and legal advisors, determines in good faith that failing to do so would likely violate its fiduciary duties. However, even in that event, the merger agreement must still be submitted to stockholders for their consideration. In certain cases where the merger agreement is terminated following such a change in recommendation or a breach of the non-solicitation provisions, the party making the change, whether First Foundation or FirstSun, may be required to pay a termination fee. See “The Merger Agreement—Termination Fees” for additional details.

Q: MAY I CHANGE MY VOTE AFTER I SUBMIT MY PROXY?

A: Yes. If you are the record holder of FirstSun common stock or First Foundation common stock, you can change your vote or revoke your proxy at any time before your proxy is voted at the applicable special meeting. You can do this by:

Simply attending the special meeting without voting will not revoke any proxy you have previously given. If your shares are held in “street name,” you must contact your bank, broker or other nominee to change your vote.

Q: HOW DOES THE FIRSTSUN BOARD OF DIRECTORS RECOMMEND THAT I VOTE?

A: The FirstSun board of directors has unanimously approved the merger agreement and determined that the merger agreement and the transactions contemplated thereby, including the merger and the issuance of FirstSun common stock in the merger, and the amendments to FirstSun’s certificate of incorporation described in this joint proxy statement/prospectus, are advisable and in the best interests of FirstSun and its stockholders. The FirstSun board of directors recommends that FirstSun stockholders vote “FOR” the FirstSun merger proposal, “FOR” the FirstSun authorized common increase proposal, “FOR” the FirstSun non-voting common stock proposal, and “FOR” the FirstSun adjournment proposal.

Q: HOW DOES THE FIRST FOUNDATION BOARD OF DIRECTORS RECOMMEND THAT I VOTE?

A: The First Foundation board of directors has unanimously approved the merger agreement and determined that the merger agreement and the transactions contemplated thereby are advisable and in the best interests of First Foundation and its stockholders. The First Foundation board of directors recommends that First Foundation stockholders vote “FOR” the First Foundation merger proposal, “FOR” the First Foundation merger compensation proposal “FOR” the First Foundation adjournment proposal and “FOR” the First Foundation amendment proposal.

Q: WHAT WILL HAPPEN IF I RETURN MY PROXY CARD WITHOUT INDICATING HOW TO VOTE?

A: If you sign and return your proxy card without indicating how to vote on any particular proposal, the shares of FirstSun common stock represented by your proxy will be voted as recommended by the FirstSun board of directors with respect to such proposal, or the shares of First Foundation common stock represented by your proxy will be voted as recommended by the First Foundation board of directors with respect to such proposal, as applicable.

Q: WHAT ARE THE CONDITIONS TO COMPLETE THE MERGER?

A: The obligations of FirstSun and First Foundation to complete the merger are subject to the satisfaction or waiver of the closing conditions contained in the merger agreement. These conditions include, among others:

In addition, FirstSun’s obligation to complete the merger is subject to the Lock-Up Agreements, the WETAs and other ancillary agreements being in full force and effect and First Foundation having consolidated tangible stockholders’ equity of no less than the minimum tangible equity threshold for the corresponding month ended (all as further described below).

For more information, see “The Merger Agreement—Conditions to Completion of the Merger” beginning on page 139.

Q: WHEN WILL THE MERGER BE COMPLETED?

A: The merger will be completed when all of the conditions to completion described in the merger agreement are satisfied or waived, including the receipt of required regulatory approvals and the expiration of all statutory waiting periods and approval of the FirstSun merger proposal, the FirstSun authorized common increase proposal and the FirstSun non-voting common stock proposal by FirstSun stockholders, and approval of the First Foundation merger proposal by First Foundation stockholders. While we currently expect the merger to be completed early in the second quarter of 2026, the actual timing will depend on the time required to obtain the required regulatory approvals and satisfy the other conditions to closing, some of which are not entirely within the control of either party.

Q: ARE FIRSTSUN STOCKHOLDERS ENTITLED TO APPRAISAL RIGHTS?

A: No. Under Section 262 of the Delaware General Corporation Law, which we refer to as the DGCL, holders of FirstSun common stock are not entitled to appraisal rights in connection with the merger because FirstSun is the surviving corporation in the merger and shares of FirstSun common stock will remain issued and outstanding.

Q: ARE FIRST FOUNDATION STOCKHOLDERS ENTITLED TO APPRAISAL RIGHTS?

A: Holders of First Foundation common stock are not entitled to appraisal rights in connection with the merger under Section 262 of the DGCL because the merger consideration consists entirely of shares of FirstSun common stock, which is a class of stock listed on a national securities exchange, and therefore the statutory conditions for appraisal rights are not satisfied for the common stock.

Holders of First Foundation Series A Noncumulative Convertible Preferred Stock, which does not vote on the merger, may have appraisal rights under Section 262 of the DGCL. Any appraisal rights, if not waived, would be exercisable only in accordance with the procedures set forth in Section 262 of the DGCL.

Q: WHAT ARE THE MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES OF THE MERGER TO U.S. FIRST FOUNDATION STOCKHOLDERS?

A: The merger is intended to qualify for U.S. federal income tax purposes as a “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended, which we refer to as the Code, and it is a condition to the obligations of both FirstSun and First Foundation to complete the merger that each receives a legal opinion to that effect. Assuming the merger so qualifies, if you are a U.S. holder of First Foundation common stock, you will generally not recognize gain or loss for U.S. federal income tax purposes on the receipt of FirstSun common stock in exchange for your First Foundation common stock. However, you will recognize gain or loss, which generally will be capital gain or loss, with respect to any cash received in lieu of a fractional share of FirstSun common stock.

The U.S. federal income tax consequences of the merger to any particular holder will depend on such holder’s particular facts and circumstances, including the holder’s tax status and tax attributes. You are urged to consult your tax advisor regarding the U.S. federal income tax consequences of the merger to you, as well as any tax consequences under state, local or non-U.S. tax laws. For more information, see “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 146.

Q: WHAT HAPPENS IF THE MERGER IS NOT COMPLETED?

A: If the merger is not completed, FirstSun and First Foundation will remain separate, independent companies. First Foundation common stockholders will not receive FirstSun common stock (or cash in lieu of fractional shares), and holders of First Foundation preferred stock or warrants will not receive the consideration described in this joint proxy statement/prospectus. In addition, if the merger agreement is terminated under certain circumstances, one party may be required to pay the other party a termination fee. Under the merger agreement, a termination fee of $45,089,000 will be payable by FirstSun, or a termination fee of $31,390,000 will be payable by First Foundation, in each case under the circumstances described under “The Merger Agreement—Termination Fees” beginning on page 142.

Q: SHOULD FIRST FOUNDATION STOCKHOLDERS SEND IN THEIR STOCK CERTIFICATES NOW?

A: No. First Foundation stockholders should not send in any stock certificates at this time. After the merger is completed, you will receive separate written instructions describing how to surrender your shares of First Foundation common stock in exchange for the merger consideration. Until then, your stock certificates should be retained because they are still valid. Please do not send your stock certificates with your proxy card.

Q: WHAT DO I DO IF I RECEIVE MORE THAN ONE JOINT PROXY STATEMENT/PROSPECTUS OR SET OF VOTING INSTRUCTIONS?

A: FirstSun stockholders and First Foundation stockholders may receive more than one set of voting materials, including multiple copies of this joint proxy statement/prospectus and multiple proxy cards or voting instruction forms. For example, if you hold shares of FirstSun common stock or First Foundation common stock in more than one brokerage account, you will receive a separate voting instruction form for each brokerage account in which you hold such shares. If you hold shares directly as a record holder and also in “street name,” you may receive more than one set of voting materials. Each proxy card or voting instruction form you receive should be completed and returned in order to ensure that all of your shares are voted.

Q: WILL A PROXY SOLICITOR BE USED?

A: No. FirstSun is not engaging a proxy solicitor in connection with the FirstSun special meeting.

[First Foundation has engaged [·] to assist in the solicitation of proxies for the First Foundation special meeting and estimates it will pay [·] a fee of approximately $[·] plus certain expenses. First Foundation has also agreed to indemnify [·] against certain losses.]

In addition, FirstSun, First Foundation and their respective directors, officers and employees may also solicit proxies personally, electronically, or by telephone, but will not receive additional compensation for doing so.

Q: WHERE CAN I FIND MORE INFORMATION ABOUT THE COMPANIES?

A: You can find more information about FirstSun and First Foundation in the sections titled “Where You Can Find More Information” and “Incorporation of Certain Documents by Reference” included in this joint proxy statement/prospectus.

Q: WHAT IS HOUSEHOLDING AND HOW DOES IT AFFECT ME?

A: The SEC permits companies and intermediaries to deliver a single copy of proxy materials to multiple stockholders at the same address under certain circumstances. If your household has multiple accounts holding FirstSun common stock or First Foundation common stock and you are receiving a single set of materials, but would prefer to receive separate sets, please contact your broker, bank or other nominee. You may request separate copies at any time and they will be provided promptly and free of charge.

Q: WHOM SHOULD I CONTACT IF I HAVE ANY QUESTIONS?

A: If you have questions about the merger or voting your shares, please contact the proxy solicitation agent for the company in which you hold shares. Contact information is provided in the forepart of this joint proxy statement/prospectus.

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This joint proxy statement/prospectus contains forward-looking statements regarding FirstSun’s and First Foundation’s outlook or expectations with respect to the merger, including the expected costs to be incurred and cost savings to be realized in connection with the merger, the expected impact of the merger on the combined company’s future financial performance (including anticipated accretion to earnings per share), the assumed purchase accounting adjustments, other key transaction assumptions, the timing of the closing of the merger and consequences of the integration of the businesses and operations of FirstSun and First Foundation. Words such as “believe,” “expect,” “anticipate,” “intend,” “estimate,” “continue,” “positions,” “plan,” “predict,” “project,” “forecast,” “guidance,” “goal,” “objective,” “prospects,” “possible” or “potential,” by future conditional verbs such as “assume,” “will,” “would,” “should,” “could” or “may,” or by variations of such words or by similar expressions are intended to identify such forward-looking statements. These forward-looking statements are subject to numerous assumptions, risks and uncertainties, which change over time, are difficult to predict and are generally beyond the control of either company. Forward-looking statements speak only as of the date they are made and FirstSun and First Foundation assume no duty to update forward-looking statements whether as a result of new information, future events or otherwise, except as required by law. Annualized, pro forma, projected and estimated numbers are used for illustrative purpose only, are not forecasts and may not reflect actual results. Actual results may differ materially from current projections.

In addition to factors identified elsewhere in this joint proxy statement/prospectus (including the “Risk Factors” beginning on page 28), the following factors, among others, could cause actual results to differ materially from forward-looking statements or historical performance:

These and other factors are representative of the risk factors that may emerge and could cause a difference between an ultimate actual outcome and a forward-looking statement.

RISK FACTORS

An investment by First Foundation stockholders in FirstSun common stock as a result of the merger involves certain risks. Certain material risks and uncertainties connected with the merger agreement and transactions contemplated thereby, including the merger and bank merger, and ownership of FirstSun common stock are discussed below. Additionally, FirstSun and First Foundation have discussed certain other material risks connected with the ownership of FirstSun common stock and with FirstSun’s business, and with the ownership of First Foundation common stock and First Foundation’s business, respectively, under the caption “Risk Factors” appearing in their Annual Reports on Form 10-K most recently filed with the SEC and their Quarterly Reports on Form 10-Q filed with the SEC for the first, second and third quarters of 2025, and may include additional or updated disclosures of such material risks in their subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K that FirstSun or First Foundation may file with the SEC after the date of this joint proxy statement/prospectus.

Holders of FirstSun common stock and holders of First Foundation common stock should carefully read and consider all of the risks described in this joint proxy statement/prospectus, as well as all other information contained herein, when deciding whether to vote for approval of the proposals at their respective stockholder meetings. These risks may adversely affect the value of FirstSun common stock that First Foundation stockholders will receive upon consummation of the merger, and could result in a significant decline in the value of FirstSun common stock, causing current holders of First Foundation common stock to lose all or part of the value of their investment following the merger.

Risks Related to the Merger

Because the exchange ratio is fixed and the market price of FirstSun common stock will fluctuate, First Foundation stockholders cannot be certain of the market value of the merger consideration they will receive.

Upon completion of the merger, each outstanding share of First Foundation common stock, except for treasury stock or shares owned by First Foundation or FirstSun (except for shares owned by First Foundation or FirstSun or any of their respective wholly owned subsidiaries, other than shares (i) held by First Foundation or FirstSun or any of their respective wholly owned subsidiaries in trust accounts, managed accounts, mutual funds and the like, or otherwise held in a fiduciary or agency capacity, that are beneficially owned by third parties, or (ii) held, directly or indirectly, by First Foundation or FirstSun or any of their respective wholly owned subsidiaries in respect of debts previously contracted, which shares will be cancelled), will be converted into the right to receive 0.16083 of a share of FirstSun common stock, with cash paid in lieu of fractional shares. Each share of First Foundation’s Series A Noncumulative Convertible Preferred Stock and Series C Non-Voting Common Equity Equivalent Stock will convert into the right to receive a number of shares of FirstSun common stock equal to the number of shares of First Foundation common stock into which such share was convertible immediately prior to the merger, multiplied by the exchange ratio. Certain recipients may elect to receive non-voting shares of FirstSun common stock to avoid exceeding applicable bank regulatory ownership thresholds. The exchange ratio is fixed in the merger agreement. Accordingly, the market value of the merger consideration will vary based on the market price of FirstSun common stock at the time the merger is completed. The market value of the merger consideration may be different from the closing price of FirstSun common stock on the date the merger was announced, on the date this joint proxy statement/prospectus is mailed to stockholders, on the date of the FirstSun and First Foundation special meetings, and on the date the merger is completed. Any change in the market price of FirstSun common stock prior to the completion of the merger will affect the value of the merger consideration that First Foundation stockholders will receive, and there will be no adjustment to the exchange ratio for changes in the market price of either FirstSun common stock or First Foundation common stock.

Changes in the market price of FirstSun common stock and First Foundation common stock may result from a variety of factors, including, but not limited to, changes in, sentiment in the market regarding FirstSun’s and First Foundation’s assets, liabilities, operations or business prospects, including market sentiment regarding FirstSun’s and/or First Foundation’s entry into the merger agreement, and any potential changes to the merger agreement.

Changes in the market price of FirstSun common stock and First Foundation common stock may result from a variety of factors, including, but not limited to, changes in market sentiment regarding the respective businesses, financial condition, performance or prospects of FirstSun and First Foundation, including market sentiment regarding their entry into the merger agreement and any developments relating to the merger. In addition, changes in the market price of FirstSun common stock and First Foundation common stock may be affected by, among other things:

Many of these factors are outside the control of FirstSun and First Foundation. As a result, at the time of the FirstSun and First Foundation special meetings, stockholders will not know the precise market value of the FirstSun common stock that First Foundation stockholders will receive in the merger. The market value of the merger consideration may be higher or lower than the value on the date the merger agreement was announced, the date this joint proxy statement/prospectus is mailed, the date of the special meetings, or the date the merger is completed. You are encouraged to obtain current market quotations for both FirstSun common stock (which is listed on Nasdaq) and First Foundation common stock (which is listed on the NYSE). As a result, at the time of the FirstSun and First Foundation special meetings, stockholders will not know the precise market value of the FirstSun common stock that First Foundation stockholders will receive in the merger. You should obtain current market quotations for both FirstSun common stock (which is listed on Nasdaq) and First Foundation common stock (which is listed on the NYSE).

The fairness opinions obtained by the boards of directors of FirstSun and First Foundation will not reflect changes in circumstances after the dates of those opinions.

The fairness opinion obtained by FirstSun’s board of directors from Stephens was delivered on, and dated, October 27, 2025, and the fairness opinions obtained by First Foundation’s board of directors from KBW and Jefferies were delivered on, and dated, October 26, 2025 and October 25, 2025, respectively, in each case prior to the signing of the merger agreement.

Each opinion was provided as of a specific date and is based on financial, market, economic, and other conditions as they existed and could be evaluated at that time. As a result, the opinions do not reflect any events or circumstances that may occur or become known after the date of each opinion. None of Stephens, KBW, or Jefferies has any obligation to update, revise, or reaffirm its opinion to reflect subsequent developments, including changes in the operations, financial condition, business, results of operations, or prospects of FirstSun or First Foundation, changes in general market or economic conditions, changes in interest rates, or other factors that may arise prior to the completion of the merger.

The success of the merger and bank merger will depend on a number of uncertain factors and may cause the market price of FirstSun common stock or First Foundation common stock to fluctuate.

The success of the merger and the bank merger is subject to numerous risks and uncertainties, many of which are beyond the control of FirstSun and First Foundation. These include, but are not limited to:

There can be no assurance that the business and operations of First Foundation will not adversely affect FirstSun’s existing profitability, that FirstSun will be able to achieve future results similar to those achieved by its existing banking business, or that FirstSun will be able to effectively manage any growth resulting from the merger. If any of these risks materialize, or if other unforeseen events occur, the anticipated benefits of the merger may not be realized, and the combined company’s business, financial condition, and results of operations could be adversely affected.

Combining FirstSun and First Foundation and the balance sheet repositioning may be more difficult, costly or time consuming than expected and FirstSun may fail to realize the anticipated benefits of the merger.

The success of the merger will depend, in part, on the ability to realize the anticipated cost savings from combining the businesses of FirstSun and First Foundation and on the successful execution of the planned balance sheet repositioning. To realize the anticipated benefits and cost savings from the merger, FirstSun and First Foundation must not only integrate and combine their businesses effectively but also dispose of certain assets of First Foundation and pay down or run off certain liabilities of First Foundation as part of the balance sheet repositioning (the “balance sheet repositioning”). Execution of the balance sheet repositioning will inherently be subject to market conditions, and there is a risk that such conditions will be less favorable than anticipated when the parties entered into the merger agreement.

While the merger agreement does not require completion of the balance sheet repositioning prior to closing, First Foundation has entered into a letter agreement with FirstSun to cooperate in good faith to consider implementing certain aspects of the balance sheet repositioning before closing. However, relevant regulatory authorities may request or require completion of certain elements of the balance sheet repositioning as a condition of approval. If First Foundation implements aspects of the balance sheet repositioning prior to closing, its earnings could be adversely affected as a standalone company, and First Foundation may not receive any compensation from FirstSun for any loss of earnings or costs incurred if the merger agreement is terminated. Additionally, satisfying the minimum consolidated tangible stockholders’ equity closing condition in the merger agreement may require First Foundation to take actions that negatively impact its ability to execute its historical strategic plan, grow its balance sheet, and generate earnings and returns for stockholders as a standalone company.

First Foundation has also entered into a series of derivative transactions at a cost of approximately $19,515,000 (the “Hedge Strategy”), intended to mitigate the risk of net changes in fair value of its earning assets, wholesale funding and corresponding goodwill during the pendency of the merger. Additional derivative transactions may be entered into. The expenses associated with the Hedge Strategy will reduce First Foundation’s net income during the pendency of the merger, and while FirstSun has agreed to reimburse certain Hedge Strategy expenses upon termination of the merger agreement in limited circumstances, there is no assurance that First Foundation will recoup those expenses, particularly if the merger agreement is terminated due to failure to obtain stockholder approval, breach of the merger agreement, or failure to satisfy the minimum consolidated tangible stockholders’ equity condition.

If FirstSun and First Foundation are not able to successfully achieve these objectives, the anticipated benefits of the merger may not be realized fully or at all or may take longer to realize than expected. In addition, the actual cost savings and anticipated benefits of the merger could be less than anticipated, and integration may result in additional unforeseen expenses. For reference, as of the date of signing the merger agreement, the pre-tax cost savings for the transaction were estimated to be approximately 35% of First Foundation’s run-rate expense base. An inability to realize the full extent of the anticipated benefits of the merger, as well as any delays encountered in the integration process or balance sheet repositioning, could have an adverse effect upon the capital position, revenues, levels of expenses, and operating results of the combined company following the completion of the merger, which may adversely affect the value of the common stock of the combined company following the completion of the merger.

FirstSun and First Foundation have operated and, until the completion of the merger, must continue to operate independently. It is possible that the integration process could result in the loss of key employees, the disruption of each company’s ongoing businesses, or inconsistencies in standards, controls, procedures, and policies that adversely affect the companies’ ability to maintain relationships with clients, customers, depositors, and employees or to achieve the anticipated benefits and cost savings of the merger. Integration efforts between the two companies may also divert management attention and resources. These integration matters could have an adverse effect on each of FirstSun and First Foundation during this transition period and for an undetermined period after completion of the merger on the combined company.

The combined company may be unable to retain First Foundation personnel successfully after the merger is completed.

The success of the merger will depend in part on the combined company’s ability to retain the talents and dedication of employees currently employed by First Foundation. The consummation of the merger will expand FirstSun’s market to include operations in California, Nevada, Florida, and Hawaii, and retaining First Foundation personnel within such markets is important to the success of the integration of the operations and business of First Foundation and the success of the combined company. It is possible that these employees may decide not to remain with First Foundation while the merger is pending or with the combined company after the merger is consummated. If employees terminate their employment, or if an insufficient number of employees are retained to maintain effective operations, the combined company’s business activities may be adversely affected and management’s attention may be diverted from successfully integrating First Foundation to hiring suitable replacements, all of which may cause the combined company’s business to suffer. In addition, FirstSun may not be able to locate suitable replacements for any such employees who leave the combined company, or to offer employment to potential replacements on reasonable terms. Further, FirstSun’s more limited operating experience in several of First Foundation’s market areas may adversely impact the combined company’s ability to successfully compete in such market areas without retaining First Foundation’s employees.

The combined company expects to incur substantial expenses related to the merger.

The combined company expects to incur substantial expenses in connection with completing the merger and combining the business, operations, networks, systems, technologies, policies and procedures of FirstSun and those of First Foundation. Although FirstSun and First Foundation have assumed that a certain level of transaction and combination expenses would be incurred, there are a number of factors beyond their control that could affect the total amount or the timing of these expenses. Many of the expenses that will be incurred, by their nature, are difficult to estimate accurately at the present time. Due to these factors, the transaction and combination expenses associated with the merger could, particularly in the near term, exceed the savings that the combined company expects to achieve from the elimination of duplicative expenses and the realization of economies of scale and cost savings related to the combination of the businesses following the completion of the merger.

In addition, before completing the merger, each of FirstSun and First Foundation will incur or have incurred substantial expenses in connection with the negotiation and completion of the transactions contemplated by the merger agreement. In preparation for the consummation of the merger, the companies will also incur additional costs and expenses associated with preparing and filing the registration statement of which this joint proxy statement/prospectus forms a part, printing and mailing this joint proxy statement/prospectus to solicit the requisite approvals of the merger proposal from both FirstSun stockholders and First Foundation stockholders, and paying all filing and other fees required by the SEC, bank regulatory authorities, and other governmental agencies in connection with the proposed merger. If the merger is not completed, FirstSun and First Foundation would have to recognize these expenses without realizing the anticipated benefits of the merger.

Regulatory approvals may not be received, may take longer than expected or may impose conditions that are not presently anticipated or that could have an adverse effect on the combined company following the merger.

Before the merger and the bank merger may be completed, various approvals, consents and non-objections must be obtained from the Federal Reserve, the OCC and other regulatory authorities without the imposition of any materially burdensome regulatory condition. In determining whether to grant these approvals, the regulators consider a variety of factors, including the regulatory standing of each party and the factors described under “The Merger—Regulatory Approvals Required for the Merger” beginning on page 115. These approvals could be delayed or not obtained at all, including due to any or all of the following: an adverse development in either party’s regulatory standing; governmental, political, community or supervisory inquiries or opposition; or changes in legislation, regulatory policy or the political environment, including changes in the leadership of regulatory agencies.

Any approvals that are granted may impose terms, conditions, limitations, obligations or costs, or place restrictions on the conduct of the combined company’s business or require changes to the terms of the transactions contemplated by the merger agreement. There can be no assurance that regulators will not impose any such conditions, limitations, obligations or restrictions, or that any such conditions, limitations, obligations or restrictions will not have the effect of delaying the completion of the merger or the bank merger, imposing additional material costs on or materially limiting the revenues of the combined company following the merger, or otherwise reducing the anticipated benefits of the merger. In addition, there can be no assurance that any such conditions, limitations, obligations or restrictions will not result in the delay or abandonment of the merger. Completion of the merger is also conditioned on the absence of certain orders, injunctions or decrees by any governmental entity that would prohibit or make illegal the completion of the merger or the bank merger.

Although the parties have agreed to use their reasonable best efforts to obtain the required regulatory approvals, neither FirstSun nor First Foundation is required under the merger agreement to agree to any condition or restriction that would reasonably be expected to result in a materially burdensome regulatory condition. See “The Merger—Regulatory Approvals Required for the Merger” beginning on page 115.

The unaudited pro forma combined financial information included in this joint proxy statement/prospectus is preliminary and the actual financial condition and results of operations of the combined company after the merger may differ materially.

The unaudited pro forma combined financial information included in this joint proxy statement/prospectus is presented for illustrative purposes only and is not necessarily indicative of the actual financial position or results of operations that the combined company would have achieved had the merger been completed on the dates indicated, nor is it necessarily indicative of the future financial position or results of operations of the combined company. The unaudited pro forma combined financial information reflects preliminary estimates and assumptions, including adjustments to record First Foundation’s identifiable assets acquired and liabilities assumed at fair value and to recognize any resulting goodwill. The fair value estimates and other pro forma adjustments are based on preliminary information and are subject to change. Final amounts will be determined based on the actual consideration paid and the fair value of First Foundation’s assets and liabilities as of the completion date of the merger, which may be affected by, among other factors, changes in interest rates and market conditions. As a result, the final acquisition accounting adjustments may differ materially from those reflected in the unaudited pro forma combined financial information presented in this joint proxy statement/prospectus.

Additionally, the unaudited pro forma combined financial information includes further adjustments related to the re-positioning strategy, which are also based on preliminary estimates, to reflect the anticipated liquidation of certain assets of First Foundation and FirstSun and the use of the proceeds to pay down certain liabilities of the combined company. Accordingly, you should not place undue reliance on the unaudited pro forma combined financial information. For more information, see the section entitled “Unaudited Pro Forma Condensed Combined Financial Information” beginning on page 149.

We may not be able to accomplish our contemplated balance sheet repositioning which could have a material adverse effect on our results of operations or financial condition.

There can be no assurance that we will be able to sell the assets we intend to sell or pay down the liabilities we intend to pay down as described under “Unaudited Pro Forma Condensed Combined Financial Information—Balance Sheet Repositioning” on the terms we expect, or at all. The sale of loans or investment securities may be affected by market conditions and will depend on the terms offered by prospective purchasers. If we are unable to complete the contemplated balance sheet repositioning, or if we are unable to do so on the terms we expect, we may not realize the anticipated benefits to our results of operations and financial condition. In addition, efforts to sell these assets may divert management’s attention and resources from our core businesses and operations, which could have a material adverse effect on our operations.

Even if we are able to execute the contemplated balance sheet repositioning as planned, we may not fully realize the anticipated benefits. For example, we may not be able to use the proceeds from asset sales as intended, or the repositioning may not have the expected effects on our net interest margin, liquidity, or portfolio positioning for potential changes in interest rates. These and other potential consequences could adversely affect our financial condition or results of operations.

Certain of First Foundation’s directors and executive officers may have interests in the merger that may differ from, or be in addition to, the interests of holders of First Foundation common stock generally.

Holders of First Foundation common stock should be aware that some of First Foundation’s directors and executive officers may have interests in the merger and have arrangements that are different from, or in addition to, those of holders of First Foundation common stock generally. These interests and arrangements may create potential conflicts of interest. The First Foundation board of directors was aware of these interests and considered these interests, among other matters, when making its decision to approve the merger and merger agreement, and in recommending that stockholders vote to approve the merger agreement. For a more complete description of these interests, please see the section entitled “The Merger—Interests of First Foundation’s Directors and Executive Officers in the Merger” beginning on page 110.

Stockholder litigation could prevent or delay the completion of the merger or otherwise negatively impact the business and operations of FirstSun and First Foundation.

Holders of common stock of FirstSun or First Foundation may file lawsuits against FirstSun, First Foundation and/or the directors and officers of either company in connection with the merger. One of the conditions to the closing of the merger is that there must be no order, injunction or decree issued by any court or governmental entity of competent jurisdiction or other legal restraint preventing the consummation of the merger or any of the other transactions contemplated by the merger agreement. If any plaintiff were successful in obtaining an injunction prohibiting FirstSun or First Foundation from completing the merger or any of the other transactions contemplated by the merger agreement, then such injunction may delay or prevent the effectiveness of the merger and could result in significant costs to FirstSun or First Foundation, including any cost associated with the indemnification of directors and officers of each company. FirstSun and First Foundation may incur costs in connection with the defense or settlement of any stockholder or stockholder lawsuits filed in connection with the merger. Such litigation could have an adverse effect on the financial condition and results of operations of FirstSun and First Foundation and could prevent or delay the completion of the merger.

The merger agreement may be terminated in accordance with its terms, and the merger may not be consummated.

The merger agreement may be terminated at any time prior to the effective time, whether before or after the receipt of the requisite FirstSun vote or the requisite First Foundation vote, in the circumstances described under “The Merger Agreement—Termination Fees” beginning on page 142. These circumstances include, among others: mutual written agreement of the parties to terminate the merger agreement; a final and non-appealable denial of a required regulatory approval or a request by a governmental entity that an application for a required regulatory approval be withdrawn under circumstances in which resubmission within the permitted time period would not be allowed; failure to complete the merger on or before the 12-month anniversary of the date of the merger agreement (subject to certain exceptions); uncured breaches of representations, warranties, covenants or agreements that would cause the failure of a closing condition, including the failure of First Foundation to maintain tangible stockholders equity in excess of minimum thresholds; a recommendation change by either FirstSun’s board of directors or First Foundation’s board of directors; or the failure to obtain the requisite FirstSun vote or the requisite First Foundation vote.

However, neither FirstSun nor First Foundation may terminate the merger agreement solely because of changes in the market price of FirstSun common stock or First Foundation common stock or solely to accept a superior proposal.

If the merger agreement is terminated under certain circumstances, a termination fee will be payable by one party to the other. If payable, the termination fee would be $45,089,000 from FirstSun to First Foundation, or $31,390,000 from First Foundation to FirstSun, depending on the circumstances. The circumstances giving rise to the termination fee obligations are described in detail under “The Merger Agreement—Termination Fees” beginning on page 142.

Termination of the merger agreement could negatively affect FirstSun and First Foundation.

If the merger is not completed for any reason, whether before or after receipt of the requisite stockholder approvals, both FirstSun and First Foundation could be adversely affected. For example, each company’s business may have been disrupted by the diversion of management attention toward the merger and related integration planning, and each company may have foregone or delayed pursuing other strategic opportunities during the pendency of the merger. In addition, market confidence in either company, its relationships with customers, depositors, employees, or counterparties, and its competitive position could be negatively impacted.

Furthermore, if the merger agreement is terminated under certain circumstances, First Foundation may be required to pay FirstSun a termination fee of $31,390,000, and if terminated under certain other circumstances, FirstSun may be required to pay First Foundation a termination fee of $45,089,000. See “The Merger Agreement—Termination Fees” beginning on page 142.

There can be no assurance that the merger agreement will not be terminated or that, if terminated, either FirstSun or First Foundation would not be required to pay a termination fee. In addition, the failure to complete the merger could result in additional costs, loss of key personnel, or other negative impacts on the ongoing business and financial condition of either company.

In connection with the merger, FirstSun will assume First Foundation’s and First Foundation Bank’s outstanding debt obligations, and the combined company’s level of indebtedness following the completion of the merger could adversely affect the combined company’s ability to manage its capital position and to meet its obligations under FirstSun’s existing indebtedness.

Upon the closing of the merger, FirstSun will assume First Foundation’s and First Foundation Bank’s outstanding indebtedness. FirstSun’s existing debt (including First Foundation’s and First Foundation Bank’s assumed indebtedness), together with any future incurrence of additional indebtedness, could have important consequences for the combined company’s creditors and stockholders. For example, it could:

First Foundation, and consequently, FirstSun will be subject to business uncertainties and contractual restrictions while the merger is pending.

Uncertainty regarding the effect of the merger on employees and customers may adversely affect First Foundation and, consequently, the combined company. Such uncertainty may impair First Foundation’s ability to attract, retain, and motivate key personnel prior to the completion of the merger, and could cause customers and other business partners to seek to alter or terminate their relationships with First Foundation. Retaining certain employees may be particularly challenging while the merger is pending, as some may be uncertain about their future roles with the combined company. If key employees or customers depart due to uncertainty, integration challenges, or a desire not to remain with First Foundation or the combined company, the business of the combined company could be harmed.

In addition, subject to certain exceptions, First Foundation has agreed to operate its business in all material respects in the usual, regular, and ordinary course and to use reasonable best efforts to maintain and preserve its business organization and its current relationships with customers, regulators, employees, and other business partners prior to closing. See “The Merger Agreement—Covenants and Agreements” for a description of the restrictive covenants applicable to First Foundation.

The merger agreement contains provisions that may discourage other companies from trying to acquire either First Foundation or FirstSun for greater merger consideration.

The merger agreement contains provisions that could discourage a third party from making an acquisition proposal for either First Foundation or FirstSun that might result in greater value to their respective stockholders than the merger or could cause a potential acquirer to propose a lower per-share price than it might otherwise offer in the absence of such provisions.

These provisions include mutual “no-shop” restrictions, which generally prohibit each of First Foundation and FirstSun from soliciting, initiating, or knowingly encouraging inquiries or proposals with respect to, or engaging in discussions or negotiations regarding, any alternative acquisition proposal. These restrictions are subject to limited exceptions that permit each board of directors to consider a Superior Proposal if necessary to comply with its fiduciary duties.

In addition, if the merger agreement is terminated under certain circumstances involving a competing acquisition proposal or a change in either party’s board recommendation, First Foundation or FirstSun may be required to pay the other party a termination fee ($31,390,000 for First Foundation and $45,089,000 for FirstSun). See “The Merger Agreement—Termination Fees” beginning on page 142.

The shares of FirstSun common stock to be received by holders of First Foundation common stock as a result of the merger will have different rights from the shares of First Foundation common stock.

In the merger, holders of First Foundation common stock will become holders of FirstSun common stock and their rights as stockholders will be governed by Delaware law and the governing documents of the combined company. The rights associated with FirstSun common stock are different from the rights associated with First Foundation common stock and preferred stock. See the section entitled “Comparison of Stockholders’ Rights” beginning on page 168 for a discussion of the different rights associated with FirstSun common stock.

Holders of First Foundation stock will have a reduced ownership and voting interest in the combined company after the merger and will exercise less influence over management.

Upon completion of the merger, each First Foundation stockholder who receives shares of FirstSun common stock will become a FirstSun stockholder. Based on the number of shares of First Foundation common stock, preferred stock, warrants, and equity awards outstanding as of the FirstSun record date, the total number of shares of FirstSun common stock estimated to be issued to holders of First Foundation stock and equity awards in connection with, and subject to, the completion of the merger is approximately 18.96 million shares.

Based on (i) the number of outstanding shares of FirstSun common stock and First Foundation common stock (including shares of First Foundation preferred stock assumed to convert into FirstSun common stock and shares issuable upon settlement of First Foundation warrants and unvested equity awards) as of November 30, 2025, (ii) the exchange ratio of 0.16083, and (iii) after giving effect to the termination and cash-out of the First Foundation warrants, it is expected that legacy FirstSun stockholders will own approximately 59.5% and legacy First Foundation stockholders approximately 40.5% of the issued and outstanding shares of FirstSun common stock immediately following the merger.

As a result, First Foundation stockholders may have less influence over the management and policies of the combined company than they currently have over First Foundation. In addition, some former First Foundation stockholders may receive non-voting shares of FirstSun common stock to avoid exceeding applicable bank regulatory ownership thresholds, which would further limit their ability to influence the management and policies of the combined company.

Certain holders may receive non-voting common stock or modified warrant terms, which could affect their voting rights and potential investment returns.

In connection with the merger, each share of First Foundation’s Series A preferred stock and Series C non-voting common equity equivalent stock will be converted into FirstSun common stock based on the number of shares of First Foundation common stock into which such share was convertible immediately prior to the merger, multiplied by the exchange ratio. In addition, warrant holders have entered into a Warrant Exercise and Termination Agreement, pursuant to which their warrants will be exercised on a cashless basis and terminated in exchange for a combination of cash and First Foundation Series C preferred stock, which will then be converted into FirstSun common stock in the merger.

Holders who would otherwise receive more than 4.99% of the outstanding FirstSun common stock upon completion of the merger may elect, by providing timely written notice, to receive non-voting FirstSun common stock for all or a portion of their shares above this threshold. As a result, certain holders may receive securities with different voting and economic characteristics than others, which may affect their ability to influence the combined company following the merger.

There may continue to be a limited trading market for FirstSun common stock, which could adversely affect the liquidity and value of your investment.

FirstSun common stock is listed on Nasdaq and trades on a daily basis. However, trading volume in FirstSun common stock has historically been more limited compared to larger publicly traded companies, and there can be no assurance regarding the level of future trading volume or the development of a more active trading market following the merger. Even if the stockholder base expands as a result of the merger, the liquidity of FirstSun common stock depends on the presence of willing buyers and sellers, which is outside of FirstSun’s control. Although the FirstSun stockholder base is expected to expand as a result of the merger, there can be no assurance that trading volumes will increase, that bid-ask spreads will narrow, or that a more active and liquid market for FirstSun common stock will develop or be sustained. Accordingly, First Foundation stockholders should consider the potential for continued variability in liquidity and price volatility with respect to FirstSun common stock following the merger, and there can be no assurance that stockholders will be able to sell their shares at the time or price they desire, including at prices that reflect or exceed the implied value of the exchange ratio.

The market price of FirstSun common stock after the merger may be affected by factors different from and in addition to those affecting the shares of First Foundation or FirstSun currently.

As a result of the merger, First Foundation stockholders will become holders of FirstSun common stock. FirstSun’s business differs from that of First Foundation. First Foundation’s business, assets, liabilities, financial condition, results of operations and prospects are of major significance with respect to the combined company. Accordingly, the business, assets, liabilities, financial condition, results of operations and prospects of the combined company and the market price of FirstSun common stock after the completion of the merger may be affected by factors different from and in addition to those currently affecting the independent business, assets, liabilities, financial condition, results of operations and prospects of FirstSun. Among other things, the net interest income, assets, such as securities and loans, and economic value of equity of the combined company are expected to have different sensitivities to changes in interest rates than the current sensitivities of net interest income, assets, such as securities and loans, and economic value of equity of FirstSun independently to changes in interest rates. For a discussion of the businesses of FirstSun and First Foundation and of certain factors to consider in connection with those businesses, see the documents incorporated by reference into this joint proxy statement/prospectus.

Issuance of shares of FirstSun common stock in connection with the merger may adversely affect the market price of FirstSun common stock.

In connection with the completion of the merger, FirstSun expects to issue approximately 18.7 million shares of FirstSun common stock to First Foundation stockholders and approximately 240.4 thousand shares of FirstSun common stock to holders of First Foundation equity awards. The issuance of these new shares will significantly increase the number of outstanding shares of FirstSun common stock, which could result in dilution to existing FirstSun stockholders. The increased supply of FirstSun common stock in the market, as well as any sales of these shares, could result in fluctuations in the market price of FirstSun common stock, including a possible decrease in the stock price. The market price may also be affected by investor perceptions regarding the merger, the combined company’s future prospects, and other factors described elsewhere in this joint proxy statement/prospectus.

Risks Relating to FirstSun’s Business

You should read and consider risk factors specific to FirstSun’s business that will also affect the combined company after the merger. These risks are described in the “Risk Factors” section of FirstSun’s Annual Report on Form 10-K for the year ended December 31, 2024, and in any updates to those risk factors set forth in FirstSun’s Quarterly Reports on Form 10-Q and in other documents incorporated by reference into this joint proxy statement/prospectus. Please see the section entitled “Where You Can Find More Information” beginning on page iii of this joint proxy statement/prospectus for the location of information incorporated by reference into this joint proxy statement/prospectus.

Risks Relating to First Foundation’s Business

You should read and consider risk factors specific to First Foundation’s business that will also affect the combined company after the merger. These risks are described in the “Risk Factors” section of First Foundation’s Annual Report on Form 10-K for the year ended December 31, 2024, and in any updates to those risk factors set forth in First Foundation’s Quarterly Reports on Form 10-Q and in other documents incorporated by reference into this joint proxy statement/prospectus. Please see the section entitled “Where You Can Find More Information” beginning on page iii of this joint proxy statement/prospectus for the location of information incorporated by reference into this joint proxy statement/prospectus.

THE FIRSTSUN SPECIAL MEETING

Date, Time and Place of the FirstSun Special Meeting

The FirstSun special meeting will be held on [·], 2026, at [·] [a.m./p.m.] Central Time and will be conducted solely by means of remote communication (virtual meeting) at [·]. Instructions for accessing the virtual meeting, voting electronically during the meeting and submitting questions are provided in this joint proxy statement/prospectus and on your proxy card. On or about [·], 2026, FirstSun commenced mailing this joint proxy statement/prospectus and the enclosed form of proxy to its stockholders entitled to vote at the FirstSun special meeting.

Record Date; Shares Entitled to Vote; List of Stockholders

The FirstSun board of directors has fixed the close of business on [·], 2026 as the record date for determining the holders of FirstSun common stock entitled to notice of and to vote at the FirstSun special meeting. Only holders of record of FirstSun common stock at the close of business on the record date will be entitled to vote at the meeting and at any adjournments or postponements thereof, provided that such shares remain outstanding on the date of the meeting. A list of stockholders entitled to vote will be available for examination during the meeting through the virtual meeting platform.

Purpose of the FirstSun Special Meeting; Matters to Be Considered

At the FirstSun special meeting, FirstSun common stockholders will be asked to consider and vote on:

Completion of the merger is conditioned on approval of each of the FirstSun merger proposal, the FirstSun authorized common increase proposal and the FirstSun non-voting common stock proposal, among other conditions. Completion of the merger is not conditioned on approval of the FirstSun adjournment proposal.

Recommendation of the FirstSun Board of Directors

The FirstSun board of directors unanimously recommends that FirstSun common stockholders vote “FOR” the FirstSun merger proposal, “FOR” the FirstSun authorized common increase proposal, “FOR” the FirstSun non-voting common stock proposal and “FOR” the FirstSun adjournment proposal. See “The Merger—FirstSun’s Reasons for the Merger” beginning on page 63.

FirstSun Record Date and Quorum

The FirstSun board of directors has fixed the close of business on [·], 2026 as the record date for determining the holders of FirstSun common stock entitled to receive notice of, and to vote at, the FirstSun special meeting. As of the FirstSun record date, there were [·] shares of FirstSun common stock outstanding and entitled to vote at the FirstSun special meeting held by [·] holders of record.

To transact business at the FirstSun special meeting, the presence, virtually or represented by proxy, of at least a majority of the total number of outstanding shares of FirstSun common stock entitled to vote at the FirstSun special meeting is necessary to constitute a quorum. Abstentions will be treated as present for purposes of determining the presence or absence of a quorum. Because the proposals are considered non-routine matters under applicable exchange rules, broker discretionary voting is not permitted and broker non-votes are not expected. If any broker non-votes occur, they will not be counted for purposes of determining whether a quorum exists. If a quorum is not present, the holders of a majority of the voting shares represented at the FirstSun special meeting, virtually or by proxy, may adjourn the meeting from time to time until a quorum is present.

FirstSun Voting Rights

Each share of FirstSun common stock entitles the holder to one vote on each proposal to be considered at the FirstSun special meeting.

Required Vote

Approval of the FirstSun merger proposal requires the affirmative vote of a majority of the issued and outstanding shares of FirstSun common stock entitled to vote thereon.

Approval of the FirstSun authorized common increase proposal requires the affirmative vote of a majority of the issued and outstanding shares of FirstSun common stock entitled to vote thereon.

Approval of the FirstSun non-voting common stock proposal requires the affirmative vote of a majority of the issued and outstanding shares of FirstSun common stock entitled to vote thereon.

Assuming a quorum is present, approval of the FirstSun adjournment proposal requires the affirmative vote of a majority of the votes cast on such proposal at the FirstSun special meeting.

Voting by FirstSun’s Directors and Executive Officers

As of the FirstSun record date, directors and executive officers of FirstSun and their affiliates owned and were entitled to vote an aggregate of approximately [·] shares of FirstSun common stock, representing approximately [·]% of the shares of FirstSun common stock outstanding on that date. FirstSun currently expects that its directors and executive officers will vote their shares in favor of the FirstSun merger proposal, the FirstSun authorized common increase proposal, the FirstSun non-voting common stock proposal and the FirstSun adjournment proposal, although none of them has entered into any agreements obligating them to do so.

Treatment of Abstentions; Failure to Vote

For the FirstSun merger proposal, the FirstSun authorized common increase proposal, and the FirstSun non-voting common stock proposal, an abstention or failure to vote, either virtually or by proxy, will have the same effect as a vote “AGAINST” such proposal. For the FirstSun adjournment proposal, an abstention will have no effect on the proposal. Because broker discretionary voting is not permitted on any of the proposals, broker non-votes are not expected.

Voting on Proxies; Incomplete Proxies

Giving a proxy means that a FirstSun stockholder authorizes the persons named in the enclosed proxy card to vote its shares of FirstSun common stock at the FirstSun special meeting in the manner such stockholder directs. A FirstSun stockholder may vote by proxy or virtually at the FirstSun special meeting. If you hold your shares of FirstSun common stock in your name as a record holder, you may submit a proxy prior to the FirstSun special meeting by any of the following methods:

When a properly executed proxy is returned prior to the FirstSun special meeting, the shares of FirstSun common stock represented by it will be voted at the FirstSun special meeting in accordance with the instructions on the proxy card. If a proxy is returned without indication as to how to vote, the shares represented by the proxy will be voted as recommended by the FirstSun board of directors.

Shares Held in “Street Name”; Broker Non-Votes

If your shares of FirstSun common stock are held in “street name” by a broker, bank or other nominee, you should follow the voting instructions provided by that firm and check whether it offers telephone or Internet voting. Under applicable exchange rules, your broker, bank or other nominee may not vote your shares on any of the proposals without your specific instructions. If you do not provide voting instructions, your shares will not be voted on any proposal at the FirstSun special meeting (a broker non-vote). Because there are no routine matters to be voted on at the FirstSun special meeting, brokers will not have discretionary authority to vote on any proposal. Broker non-votes, if any, will have the same effect as a vote “AGAINST” the FirstSun merger proposal, the FirstSun authorized common increase proposal, and the FirstSun non-voting common stock proposal, and will have no effect on the FirstSun adjournment proposal.

Your Vote Is Very Important

Your vote is very important, regardless of the number of shares of FirstSun common stock you own. Accordingly, each FirstSun stockholder should complete, sign, date and return the enclosed proxy card in the enclosed postage-paid envelope, or vote via the Internet or by telephone as soon as possible, whether or not you plan to attend the FirstSun special meeting virtually.

Revocability of Proxies and Changes to a FirstSun Stockholder’s Vote

If you are the owner of record of your shares and have submitted your proxy and would like to revoke it, you may do so before your shares of FirstSun common stock are voted at the FirstSun special meeting by taking any of the following actions:

If you choose to send a written notice of revocation or to mail a new proxy to FirstSun, you must submit your notice of revocation or your new proxy to FirstSun Capital Bancorp, Attention: Corporate Secretary, FirstSun Capital Bancorp, 1400 16th Street, Suite 250, Denver, Colorado 80202, and it must be received at any time before the vote is taken at the FirstSun special meeting.

If you have instructed a broker, bank or other nominee to vote your shares of FirstSun common stock, you must follow the directions you receive from your broker, bank or other nominee in order to change or revoke your vote.

Attending the Virtual FirstSun Special Meeting

All FirstSun stockholders of record as of the FirstSun record date, or their duly appointed proxies, may attend the virtual FirstSun special meeting. To attend, vote, and submit questions during the virtual meeting, please go to [·] and enter the control number printed on your Notice of Internet Availability, proxy card or voting instruction form. The webcast will begin promptly at [·] [a.m./p.m.] Central Time on [·], 2026, and online check-in will open at [·] [a.m./p.m.] Central Time. A list of stockholders of record will be available for inspection during the meeting through the virtual meeting website. Technical support information will be available on the meeting website.

Inspector of Election; Tabulation of Votes

All votes properly cast and all proxies properly submitted and unrevoked will be tabulated by the inspector of election appointed for the FirstSun special meeting. The inspector of election will determine the presence of a quorum, the validity of proxies and ballots and the results of the voting.

Solicitation of Proxies

The cost of solicitation of proxies for the FirstSun special meeting will be borne by FirstSun. FirstSun will reimburse brokerage firms and other custodians, nominees and fiduciaries for reasonable expenses incurred by them in sending proxy materials to the beneficial owners of FirstSun common stock. FirstSun has not engaged any proxy solicitation firm in connection with the solicitation of proxies. In addition, FirstSun’s directors, officers and employees may solicit proxies by mail, telephone, facsimile, electronic mail or personal contact, but no additional compensation will be paid to them for doing so.

Adjournments and Postponements

The FirstSun special meeting may be adjourned or postponed from time to time, including to solicit additional proxies if there are insufficient votes to approve any of the FirstSun merger proposal, the FirstSun authorized common increase proposal or the FirstSun non-voting common stock proposal. If the FirstSun special meeting is adjourned or postponed, your proxy will remain valid and may be voted at the adjourned or postponed meeting unless you have revoked it.

FIRSTSUN PROPOSALS

Proposal 1 — FirstSun Merger Proposal

At the FirstSun special meeting, the FirstSun stockholders will be asked to adopt the Agreement and Plan of Merger, dated as of October 27, 2025, by and between FirstSun and First Foundation, and to approve the issuance of shares of FirstSun common stock as merger consideration pursuant to the merger agreement (the FirstSun merger proposal). FirstSun stockholders should read this joint proxy statement/prospectus carefully and in its entirety, including the annexes, for more detailed information concerning the merger agreement and the merger. A copy of the merger agreement is attached to this joint proxy statement/prospectus as Annex A.

After careful consideration, the FirstSun board of directors approved the merger agreement and declared it advisable, authorized and approved the merger and the transactions contemplated thereby, and determined that the merger agreement and the merger are fair to, advisable and in the best interests of FirstSun and its stockholders. In reaching its decision, the FirstSun board of directors considered a number of factors, which are described under “The Merger—FirstSun’s Reasons for the Merger” beginning on page 63.

The FirstSun board of directors unanimously recommends that FirstSun stockholders vote “FOR” the FirstSun merger proposal.

Required Vote

Approval of the FirstSun merger proposal requires the affirmative vote of a majority of the outstanding shares of FirstSun common stock entitled to vote on the proposal. Abstentions and broker non-votes will have the same effect as votes cast “AGAINST” this proposal.

Proposal 2 — FirstSun Authorized Common Increase Proposal

FirstSun stockholders are being asked to approve an amendment to Article IV, Section 4.01 of FirstSun’s Amended and Restated Certificate of Incorporation, as amended, to increase the number of authorized shares of FirstSun common stock, par value $0.0001 per share, from 50,000,000 shares to 80,000,000 shares. The number of authorized shares of FirstSun preferred stock, par value $0.0001 per share, will remain 10,000,000 shares. This proposal is referred to as the FirstSun authorized common increase proposal.

This authorized share increase is being presented in connection with the merger. FirstSun currently has a sufficient number of authorized and unissued shares of FirstSun common stock to issue the merger consideration and to assume and convert First Foundation equity awards in accordance with the merger agreement. However, the merger will result in the issuance of a substantial number of shares of FirstSun common stock, which will significantly reduce the number of authorized shares that will remain available after closing.

Following the merger, FirstSun would have limited flexibility to issue shares for general corporate purposes, including equity compensation, capital planning, and potential strategic opportunities, unless the authorized share amount is increased at this time. This authorized common increase proposal is therefore intended to ensure appropriate post-closing capital structure flexibility.

Condition to Completion of the Merger

Although FirstSun currently has a sufficient number of authorized shares of FirstSun common stock to issue the merger consideration and to assume and convert First Foundation equity awards, the merger agreement requires that FirstSun stockholders approve this amendment to increase the number of authorized shares of FirstSun common stock as a condition to closing.

Text of Proposed Amendment

The full text of the amendment to increase the authorized shares of FirstSun common stock is set forth in the Certificate of Amendment attached as Annex E to this joint proxy statement/prospectus.

Purpose of the Amendment

The board of directors of FirstSun believes that it is important for FirstSun to maintain an appropriate level of authorized but unissued shares of FirstSun common stock following the merger. The merger will reduce the number of authorized shares of FirstSun common stock that remain available, and without this amendment, FirstSun may not have adequate flexibility to:

Effect on Existing Stockholders

This proposal does not itself result in the issuance of any shares of FirstSun common stock. Any future issuances of FirstSun common stock will be subject to approval by the FirstSun board of directors and, where applicable, compliance with Nasdaq listing rules.

Stockholders of FirstSun do not have preemptive rights.

Required Vote

Approval of the FirstSun authorized common increase proposal requires the affirmative vote of a majority of the outstanding shares of FirstSun common stock entitled to vote on the proposal. Abstentions and broker non-votes will have the same effect as votes cast “AGAINST” this proposal.

Effect of Failure to Approve the Proposal

Approval of this proposal is a condition to the completion of the merger under the merger agreement. If this proposal is not approved by FirstSun stockholders, the merger will not be completed, unless the merger agreement is amended, which is not currently contemplated and is not assured.

The FirstSun board of directors unanimously recommends that FirstSun stockholders vote “FOR” the FirstSun authorized common increase proposal.

Proposal 3 — FirstSun Non-Voting Common Stock Proposal

FirstSun stockholders are being asked to approve an amendment to Article IV of FirstSun’s Amended and Restated Certificate of Incorporation to authorize a class of non-voting common stock, par value $0.0001 per share (the “non-voting common stock”), and to authorize 20,000,000 shares of such non-voting common stock (which is in addition to the 80,000,000 shares of authorized common stock requested in the FirstSun authorized common increase proposal). This proposal is referred to as the FirstSun non-voting common stock proposal.

The non-voting common stock will have the powers, rights, preferences and limitations set forth in Exhibit A to the Certificate of Amendment, the form of which is attached to this joint proxy statement/prospectus as Annex E.

Condition to Completion of the Merger

The merger agreement requires that FirstSun stockholders approve the amendment to authorize the non-voting common stock as a condition to closing, in order to permit eligible First Foundation stockholders to elect to receive non-voting common stock in lieu of common stock to avoid exceeding the 4.99% ownership threshold.

Purpose of the Non-Voting Common Stock

As described in the section of this joint proxy statement/prospectus entitled “The Merger Agreement—Merger Consideration,” holders of First Foundation stock who would otherwise receive, as a result of the merger, shares of FirstSun common stock that would cause such holder to own more than 4.99% of the total outstanding shares of FirstSun common stock immediately following the merger may elect to receive shares of non-voting common stock in lieu of the portion of such shares that would exceed the 4.99% ownership threshold.

This election mechanism is intended to enable certain First Foundation stockholders to avoid exceeding bank regulatory, charter, contractual, or policy-based ownership limitations while still receiving full economic value of the merger consideration.

The creation of the non-voting common stock is therefore being submitted in connection with the merger to accommodate such elections. This proposal does not affect the exchange ratio or the aggregate value of the merger consideration.

Summary of Key Characteristics of the Non-Voting Common Stock

As set forth in Exhibit A to the Certificate of Amendment:

Text of Amendment

The full text of the amendment to authorize the non-voting common stock and add Exhibit A to the Certificate of Amendment describing its rights is contained in Annex E to this joint proxy statement/prospectus.

Effect on Existing Stockholders

This proposal does not modify the rights of existing holders of FirstSun common stock. Existing stockholders of FirstSun do not have preemptive rights to purchase shares of any class of FirstSun capital stock.

Required Vote

Approval of the FirstSun non-voting common stock proposal requires the affirmative vote of a majority of the outstanding shares of FirstSun common stock entitled to vote on the proposal. Abstentions and broker non-votes will have the same effect as votes cast “AGAINST” this proposal.

Effect of Failure to Approve the Proposal

Approval of this proposal is a condition to the completion of the merger under the merger agreement. If this proposal is not approved by FirstSun stockholders, the merger will not be completed, unless the merger agreement is amended, which is not currently contemplated and is not assured.

The FirstSun board of directors unanimously recommends that FirstSun stockholders vote “FOR” the FirstSun non-voting common stock proposal.

Proposal 4 — FirstSun Adjournment Proposal

FirstSun stockholders will be asked to approve a proposal to adjourn the FirstSun special meeting, if necessary or appropriate, to solicit additional proxies in favor of the FirstSun merger proposal, the FirstSun authorized common increase proposal, or the FirstSun non-voting common stock proposal (the FirstSun adjournment proposal).

Assuming a quorum is present, approval of the FirstSun adjournment proposal requires the affirmative vote of a majority of the votes cast on such proposal.

The FirstSun board of directors unanimously recommends that FirstSun stockholders vote “FOR” the FirstSun adjournment proposal.

FIRST FOUNDATION SPECIAL MEETING

Date, Time and Place of the First Foundation Special Meeting

The First Foundation special meeting will be held on [·], 2026, at [·] at [·] [a.m./p.m.] Pacific Time. On or about [·], 2026, First Foundation commenced mailing this joint proxy statement/prospectus and the enclosed form of proxy to its stockholders entitled to vote at the First Foundation special meeting.

Record Date; Shares Entitled to Vote; List of Stockholders

The First Foundation board of directors has fixed the close of business on [·], 2026 as the record date for determining the holders of First Foundation common stock entitled to notice of and to vote at the First Foundation special meeting. Only holders of record of First Foundation common stock at the close of business on the record date will be entitled to vote at the meeting and at any adjournments or postponements thereof, provided that such shares remain outstanding on the date of the meeting.

Purpose of the First Foundation Special Meeting; Matters to Be Considered

At the First Foundation special meeting, First Foundation common stockholders will be asked to consider and vote on:

Completion of the merger is conditioned on approval of the First Foundation merger proposal, among other conditions. Completion of the merger is not conditioned on approval of the First Foundation merger compensation proposal, the First Foundation adjournment proposal, and the First Foundation amendment proposal.

Recommendation of the First Foundation Board of Directors

The First Foundation board of directors unanimously recommends that First Foundation common stockholders vote “FOR” the First Foundation merger proposal, “FOR” the First Foundation merger compensation proposal, “FOR” the First Foundation adjournment proposal and “FOR” the First Foundation amendment proposal. See “The Merger—First Foundation’s Reasons for the Merger” beginning on page 66.

First Foundation Record Date and Quorum

The First Foundation board of directors has fixed the close of business on [·], 2026 as the record date for determining the holders of First Foundation common stock entitled to receive notice of, and to vote at, the First Foundation special meeting. As of the First Foundation record date, there were [·] shares of First Foundation common stock outstanding and entitled to vote at the First Foundation special meeting held by [·] holders of record.

To transact business at the First Foundation special meeting, the presence, in person or represented by proxy, of holders of a majority of the voting power entitled to vote at the meeting is necessary to constitute a quorum for the First Foundation special meeting. Abstentions will be treated as present for purposes of determining the presence or absence of a quorum. Because the proposals are considered non-routine matters under applicable exchange rules, broker discretionary voting is not permitted and broker non-votes are not expected. If any broker non-votes occur, they will be counted as present for purposes of determining whether a quorum exists, to the extent permitted by applicable law or the rules of the applicable stock exchange. If a quorum is not present, the holders of a majority of the voting shares represented at the First Foundation special meeting, in person or by proxy, may adjourn the meeting from time to time until a quorum is present.

First Foundation Voting Rights

Each share of First Foundation common stock entitles the holder to one vote on each proposal to be considered at the First Foundation special meeting.

Required Vote

Approval of the First Foundation merger proposal requires the affirmative vote of a majority of the issued and outstanding shares of First Foundation common stock entitled to vote thereon.

Assuming a quorum is present, approval of the First Foundation merger compensation proposal requires the affirmative vote of holders of a majority of voting power entitled to vote thereon, present in person or represented by proxy, at the First Foundation special meeting.

Assuming a quorum is present, approval of the First Foundation adjournment proposal requires the affirmative vote of holders of a majority of voting power entitled to vote thereon, present in person or represented by proxy, at the First Foundation special meeting.

Assuming a quorum is present, approval of the First Foundation amendment proposal requires the affirmative vote of holders of a majority of voting power entitled to vote thereon, present in person or represented by proxy, at the First Foundation special meeting.

Voting by First Foundation’s Directors and Executive Officers

As of the First Foundation record date, directors and executive officers of First Foundation and their affiliates owned and were entitled to vote an aggregate of approximately [·] shares of First Foundation common stock, representing approximately [·]% of the shares of First Foundation common stock outstanding on that date. First Foundation currently expects that its directors and executive officers will vote their shares in favor of the First Foundation merger proposal, the First Foundation merger compensation proposal and the First Foundation adjournment proposal.

Treatment of Abstentions; Failure to Vote

For the First Foundation merger proposal, an abstention or failure to vote, either in person or by proxy, will have the same effect as a vote “AGAINST” such proposal. For the First Foundation merger compensation proposal, the First Foundation adjournment proposal and the First Foundation amendment proposal, an abstention will be considered present but not voted affirmatively and thus will have the effect of a vote “AGAINST” the proposal. Because broker discretionary voting is not permitted on any of the proposals, broker non-votes are not expected. If any broker non-votes occur, they will not be counted as present for purposes of determining the outcome of these proposals (except for establishing a quorum).

Voting on Proxies; Incomplete Proxies

Giving a proxy means that a First Foundation stockholder authorizes the persons named in the enclosed proxy card to vote its shares of First Foundation common stock at the First Foundation special meeting in the manner such stockholder directs. A First Foundation common stockholder may vote by proxy or in person at the First Foundation special meeting. If you hold your shares of First Foundation common stock in your name as a record holder, you may submit a proxy prior to the First Foundation special meeting by any of the following methods:

When a properly executed proxy is returned prior to the First Foundation special meeting, the shares of First Foundation common stock represented by it will be voted at the First Foundation special meeting in accordance with the instructions on the proxy card. If a proxy is returned without indication as to how to vote, the shares represented by the proxy will be voted as recommended by the First Foundation board of directors.

Shares Held in “Street Name”; Broker Non-Votes

If your shares of First Foundation common stock are held in “street name” by a broker, bank or other nominee, you should follow the voting instructions provided by that firm and check whether it offers telephone or Internet voting. Under applicable exchange rules, your broker, bank or other nominee may not vote your shares on any of the proposals without your specific instructions. If you do not provide voting instructions, your shares will not be voted on any proposal at the First Foundation special meeting (a broker non-vote). Broker non-votes, if any, will have the same effect as a vote “AGAINST” the First Foundation merger proposal and will have no effect on the First Foundation merger compensation proposal, and the First Foundation adjournment proposal.

Your Vote Is Very Important

Your vote is very important, regardless of the number of shares of First Foundation common stock you own. Accordingly, each First Foundation common stockholder should complete, sign, date and return the enclosed proxy card in the enclosed postage-paid envelope, or vote via the Internet or by telephone as soon as possible, whether or not you plan to attend the First Foundation special meeting.

Revocability of Proxies and Changes to a First Foundation Stockholder’s Vote

If you are the owner of record of your shares and have submitted your proxy and would like to revoke it, you may do so before your shares of First Foundation common stock are voted at the First Foundation special meeting by taking any of the following actions:

If you choose to send a written notice of revocation or to mail a new proxy to First Foundation, you must submit your notice of revocation or your new proxy to First Foundation Inc., Attention: Corporate Secretary, First Foundation Inc., 5221 N. O’Connor Blvd., Suite 1375 Irving, Texas, and it must be received at any time before the vote is taken at the First Foundation special meeting.

If you have instructed a broker, bank or other nominee to vote your shares of First Foundation common stock, you must follow the directions you receive from your broker, bank or other nominee to change or revoke your vote.

Attending the First Foundation Special Meeting

All shareholders of First Foundation as of the First Foundation record date, including shareholders of record and shareholders who hold their shares in “street name” through banks, brokers, nominees or any other holder of record as of the First Foundation record date, are invited to attend the First Foundation special meeting. Shareholders of record of First Foundation common stock can vote in person at the First Foundation special meeting. If you are not a shareholder of record as of the First Foundation record date, you must obtain a proxy card, executed in your favor, from the record holder of your shares, such as a broker, bank or other nominee, to be able to vote in person at the First Foundation special meeting. If you plan to attend the First Foundation special meeting, you must hold your shares in your own name or have a letter from the record holder of your shares confirming your ownership. In addition, all First Foundation shareholders must bring a form of personal photo identification with you to be admitted. First Foundation reserves the right to refuse admittance to anyone without proper proof of share ownership or without proper photo identification. The use of cameras, sound recording equipment, communications devices or any similar equipment during the First Foundation special meeting is prohibited without First Foundation’s express written consent.

 A First Foundation shareholder who holds shares in “street name” through a broker, bank, trustee or other nominee who desires to attend the First Foundation special meeting in person must bring proof of beneficial ownership as of the First Foundation record date, such as a letter from the broker, bank, trustee or other nominee that is the record owner of such beneficial owner’s shares, a brokerage account statement or the voting instruction form provided by the broker.

Inspector of Election; Tabulation of Votes

All votes properly cast and all proxies properly submitted and unrevoked will be tabulated by the inspector of election appointed for the First Foundation special meeting. The inspector of election will determine the presence of a quorum, the validity of proxies and ballots and the results of the voting.

Solicitation of Proxies

The cost of solicitation of proxies for the First Foundation special meeting will be borne by First Foundation. First Foundation will reimburse brokerage firms and other custodians, nominees and fiduciaries for reasonable expenses incurred by them in sending proxy materials to the beneficial owners of First Foundation common stock. First Foundation has engaged [·] to assist in the solicitation of proxies for a fee of approximately $[·] plus reasonable out-of-pocket expenses. In addition, First Foundation’s directors, officers and employees may solicit proxies by mail, telephone, facsimile, electronic mail or personal contact, but no additional compensation will be paid to them for doing so.

Adjournments and Postponements

The First Foundation special meeting may be adjourned or postponed from time to time, including to solicit additional proxies if there are insufficient votes to approve any of the First Foundation merger proposal. If the First Foundation special meeting is adjourned or postponed, your proxy will remain valid and may be voted at the adjourned or postponed meeting unless you have revoked it.

FIRST FOUNDATION PROPOSALS

Proposal 1 — First Foundation Merger Proposal

At the First Foundation special meeting, the First Foundation common stockholders will be asked to adopt the Agreement and Plan of Merger, dated as of October 27, 2025, by and between FirstSun and First Foundation (the “First Foundation merger proposal”). First Foundation stockholders should read this joint proxy statement/prospectus carefully and in its entirety, including the annexes, for more detailed information concerning the merger agreement and the merger. A copy of the merger agreement is attached to this joint proxy statement/prospectus as Annex A.

After careful consideration, the First Foundation board of directors approved the merger agreement and declared it advisable, authorized and approved the merger and the transactions contemplated thereby, and determined that the merger agreement and the merger are fair to, advisable and in the best interests of First Foundation and its stockholders. In reaching its decision, the First Foundation board of directors considered a number of factors, which are described under “The Merger—First Foundation’s Reasons for the Merger” beginning on page 66.

The First Foundation board of directors unanimously recommends that First Foundation common stockholders vote “FOR” the First Foundation merger proposal.

Proposal 2 — First Foundation Merger Compensation Proposal

Pursuant to Section 14A of the Exchange Act and Rule 14a-21(c) thereunder, First Foundation is seeking a non-binding, advisory stockholder approval of the compensation of First Foundation’s named executive officers that is based on or otherwise relates to the merger. The proposal gives holders of First Foundation common stock the opportunity to express their views on the merger-related compensation of First Foundation’s named executive officers. This compensation is summarized in the table entitled “The Merger—Interests of First Foundation’s Directors and Executive Officers in the Merger—Say-on-Pay” that begins on page 112, including the associated narrative disclosure.

Accordingly, First Foundation is recommending holders of First Foundation common stock to vote FOR the adoption of the following resolution, on a non-binding advisory basis:

“RESOLVED, that the compensation that will or may be paid or become payable to First Foundation’s named executive officers, in connection with the merger, as disclosed in the table entitled “Say-on-Pay” that begins on page 112 of the joint proxy statement/prospectus for the merger, together with the accompanying footnotes and narrative discussion relating to the named executive officers’ golden parachute compensation and the agreements or understandings pursuant to which such compensation will or may be paid or become payable, in each case as disclosed pursuant to Item 402(t) of Regulation S-K in “The Merger—Interests of First Foundation’s Directors and Executive Officers in the Merger—Say-on-Pay” are hereby APPROVED.”

The vote on the advisory First Foundation merger compensation proposal is a vote separate and apart from the votes on the First Foundation merger proposal and the First Foundation adjournment proposal. Accordingly, if you are a holder of First Foundation common stock, you may vote to approve the First Foundation merger proposal and/or the First Foundation adjournment proposal and vote not to approve the First Foundation merger compensation proposal, and vice versa. The approval of the First Foundation merger compensation proposal by holders of First Foundation common stock is not a condition to the completion of the merger. If the merger is completed, the merger-related compensation will be paid to First Foundation’s named executive officers to the extent payable in accordance with the terms of the compensation agreements and arrangements even if holders of First Foundation common stock fail to approve the advisory vote regarding merger-related compensation.

Proposal 3 — First Foundation Adjournment Proposal

First Foundation common stockholders will be asked to approve a proposal to adjourn the First Foundation special meeting, if necessary or appropriate, to solicit additional proxies in favor of the First Foundation merger proposal (the “First Foundation adjournment proposal”).

The First Foundation board of directors unanimously recommends that First Foundation common stockholders vote “FOR” the First Foundation adjournment proposal.

Proposal 4 — First Foundation Amendment Proposal

First Foundation stockholders are being asked to approve, on a non-binding, advisory basis, an amendment to Article IV, Section 4.01 of FirstSun’s Amended and Restated Certificate of Incorporation (the “amendment”), as amended, to do the following:

While FirstSun currently has sufficient authorized shares to issue the merger consideration and assume First Foundation equity awards, the merger will result in the issuance of a substantial number of shares of FirstSun common stock, significantly reducing the number of authorized shares available for future use. Increasing the authorized common shares now will provide flexibility for FirstSun for future equity compensation awards, regulatory capital planning, strategic transactions and growth initiatives and other corporate purposes in the long-term interests of stockholders.

In addition, the authorization of non-voting common stock is intended to accommodate certain First Foundation stockholders who, as a result of the merger, would otherwise exceed the 4.99% ownership threshold. These stockholders may elect to receive non-voting common stock in lieu of common stock for the portion exceeding 4.99%, thereby avoiding regulatory, charter, or policy-based ownership limitations while preserving full economic value of the merger consideration. This will not affect the exchange ratio or aggregate merger consideration.

The full text of the amendment is set forth in the Certificate of Amendment attached as Annex E to this joint proxy statement/prospectus.

Although the amendment relates to FirstSun’s certificate of incorporation, FirstSun is not seeking approval of the amendment from First Foundation stockholders in their capacity as securityholders of FirstSun. Rather, because the amendment is directly related to the capitalization structure of the combined company and is integral to the overall transaction presented to First Foundation stockholders, First Foundation is requesting an advisory, non-binding vote from its stockholders to provide input on these changes to FirstSun’s governing documents. This advisory vote is intended to give First Foundation stockholders an opportunity to express their views on certain post-closing capitalization matters that will apply to them as future stockholders of FirstSun following completion of the merger. The results of this advisory vote will not obligate FirstSun to implement or abandon the amendment, and the FirstSun board of directors will retain full authority under applicable law to determine whether to effect the amendment.

This advisory vote on the First Foundation amendment proposal is a vote separate and apart from the votes on the First Foundation merger proposal and the First Foundation adjournment proposal. Accordingly, if you are a holder of First Foundation common stock, you may vote to approve the First Foundation merger proposal and/or the First Foundation adjournment proposal and vote not to approve the First Foundation amendment proposal, and vice versa. The approval of the First Foundation amendment proposal by holders of First Foundation common stock is not a condition to the completion of the merger. 

THE MERGER

The following discussion contains certain information about the merger. The discussion is subject, and qualified in its entirety by reference, to the merger agreement attached as Annex A to this joint proxy statement/prospectus and incorporated herein by reference. We urge you to read carefully this entire joint proxy statement/prospectus, including the merger agreement attached as Annex A, for a more complete understanding of the merger.

Terms of the Merger

Each of the FirstSun board of directors and the First Foundation board of directors has approved the merger agreement. Under the merger agreement, First Foundation will merge with and into FirstSun, with FirstSun continuing as the surviving corporation (the “merger”). Immediately following completion of the merger, First Foundation’s wholly owned subsidiary, First Foundation Bank, a California state-chartered bank, will merge with and into FirstSun’s wholly owned subsidiary, Sunflower Bank, National Association, a national banking association, with Sunflower Bank continuing as the surviving bank (the “bank merger”).

If the merger is completed, each outstanding share of First Foundation common stock issued and outstanding immediately prior to the effective time of the merger (except for shares owned by First Foundation or FirstSun or any of their respective wholly owned subsidiaries, other than shares (i) held by First Foundation or FirstSun or any of their respective wholly owned subsidiaries in trust accounts, managed accounts, mutual funds and the like, or otherwise held in a fiduciary or agency capacity, that are beneficially owned by third parties, or (ii) held, directly or indirectly, by First Foundation or FirstSun or any of their respective wholly owned subsidiaries in respect of debts previously contracted, which shares will be cancelled) will be converted into the right to receive 0.16083 of a share of FirstSun common stock, plus cash in lieu of any fractional shares.

No fractional shares of FirstSun common stock will be issued in the merger. Instead, each First Foundation stockholder who otherwise would have received a fractional share will receive an amount in cash (without interest) equal to the fractional portion multiplied by the average of the closing-sale prices of FirstSun common stock on Nasdaq for the five consecutive trading days ending on the trading day immediately preceding the closing date, as reported by The Wall Street Journal (or another mutually agreed source), multiplied by the exchange ratio.

In addition, each outstanding share of First Foundation Series A Noncumulative Convertible Preferred Stock and each outstanding share of First Foundation Series C Non-Voting Common Equity Equivalent Stock, which are currently convertible into First Foundation common stock at the rate of 1,000 shares of First Foundation common stock per share of preferred stock, will be converted into the right to receive 0.16083 of a share of FirstSun common stock for the number of shares of First Foundation common stock into which such shares were convertible immediately prior to the effective time, subject to the same cancellation provisions described above. If the conversion rate of First Foundation preferred stock to First Foundation common stock is adjusted prior to the closing of the merger, the exchange ratio would be proportionately adjusted.

Based on (i) the number of outstanding shares of FirstSun common stock and First Foundation common stock (including shares of First Foundation preferred stock assumed to convert into FirstSun common stock and shares issuable upon settlement of unvested First Foundation equity awards) as of November 30, 2025, (ii) the exchange ratio of 0.16083, and (iii) after giving effect to the termination and cash-out of the First Foundation warrants, it is expected that legacy FirstSun stockholders will own approximately 59.5% and legacy First Foundation stockholders approximately 40.5% of the issued and outstanding shares of FirstSun common stock immediately following the merger.

FirstSun and First Foundation stockholders are being asked to approve the merger agreement. See “The Merger Agreement” for additional and more detailed information regarding the legal documents that govern the merger, including the conditions to completion of the merger and the provisions for terminating or amending the merger agreement.

Background of the Merger

Over the years, First Foundation and FirstSun have maintained intermittent dialogue regarding potential opportunities for a strategic partnership. In 2022 and 2023, First Foundation and FirstSun engaged in discussions regarding a potential merger and conducted due diligence to evaluate strategic alignment and transaction feasibility. These discussions included a review of financial performance, market positioning, and integration considerations. After assessing the potential benefits and challenges, the parties determined that their respective strategic visions for the combined company were not aligned at the time, and the merger discussions were discontinued. KBW was FirstSun’s financial advisor during these discussions, and Stephens was First Foundation’s financial advisor during these discussions.

In connection with First Foundation’s ongoing evaluation of business objectives, near- and long-term strategies, value prospects, and the recent change in leadership, First Foundation senior management began planning in January and February of 2025 for a comprehensive strategic review to be presented in the May 2025 board of directors meeting. The topics to be addressed were to include First Foundation’s businesses and prospects, as well as macroeconomic, banking industry, and regulatory factors that could likely influence the strategic options available for First Foundation to consider and possibly pursue. The goal of the analysis was to identify various strengths, weaknesses, opportunities, and threats to the First Foundation banking and wealth management platforms, as well as to identify possible pathways to enhance stockholder value. As part of the review, senior management would consider and evaluate various strategic alternatives, including performance improvement, balance sheet repositioning, lateral hiring of proven lending teams, organic growth, capital allocation, divestitures of non-core businesses, and other business combination transactions.

Similarly, FirstSun’s board of directors and senior management have from time to time engaged in reviews and discussions of long-term strategies and objectives and have considered ways to enhance FirstSun’s performance and prospects in light of competitive, regulatory and other relevant developments, all with the goal of increasing long-term value for FirstSun’s stockholders. For FirstSun, these reviews have included periodic discussions with respect to potential transactions that would further its strategic objectives and the potential benefits and risks of any such transactions.

In February and March of 2025, First Foundation senior management met with representatives of KBW to discuss possible strategies for First Foundation to reduce the concentration of CRE-backed loans relative to total risk-based capital, as well as alternative sources of funding to lessen First Foundation’s reliance on its relatively large wholesale deposit relationships. First Foundation senior management expressed interest in continued efforts to reduce wholesale funding reliance, add new sources of deposits, and diversify the loan portfolio to reduce multi-family real estate lending through loan sales and additional securitizations.

During this same time, given its recently expanded branch footprint in Southern California, FirstSun began to focus on potential merger partners that would enhance FirstSun’s presence in this market, including First Foundation and First Foundation Bank, which has an established branch footprint and deposit base in Southern California.

On February 24, 2025, Neal Arnold (“Mr. Arnold”) met with Thomas Shafer (“Mr. Shafer”) to re-introduce FirstSun to First Foundation and to discuss Mr. Arnold’s interest in further expanding the FirstSun footprint into the California market. During the conversation, Mr. Shafer highlighted, among other things, the strength of First Foundation’s wealth management business and its strategic importance within commercial banking. This discussion occurred against the backdrop of ongoing CEO-level conversations with their respective boards of directors regarding long-term strategic priorities, including geographic expansion and diversification of revenue streams in a rapidly evolving banking landscape. Mr. Shafer and Mr. Arnold discussed various challenges facing the industry, including competitive pressures, credit quality considerations and actual performance trends. Both sides acknowledged that certain challenges, particularly those related to growth and market dynamics, were not receding and would require proactive strategies, such as strategic partnerships to achieve scale and diversification, to address. As a result of these discussions, FirstSun and First Foundation agreed to engage in further discussions regarding a possible transaction.

Between March 4 and 14, 2025, senior management of First Foundation met with representatives of KBW to discuss a potential combination of First Foundation and FirstSun, including the strategic rationale for both parties, the potential financial impact of such a merger, the potential transaction structures available, and possible next steps, which included an in-person meeting between the management of First Foundation and representatives of KBW for management to evaluate the possibility of a merger with FirstSun in greater detail with KBW’s assistance.

On March 14, 2025, Mr. Shafer and Mr. Arnold met in Atlanta, Georgia with representatives of KBW and Nelson Mullins also in attendance, to discuss a potential all-stock merger between First Foundation and FirstSun. The meeting included a comprehensive review of each company’s operations and recent developments, as well as illustrative merger structures for mutual consideration. Topics covered included the strategic rationale for the transaction, anticipated financial impact on both institutions and their respective stockholder groups, form of consideration, combined balance sheet and earnings capacity, potential synergies, complementary business “fit”, and long-term growth prospects for the combined organization. Mr. Shafer and Mr. Arnold also discussed contributions by each entity and reviewed preliminary assumptions and ranges of potential outcomes. Additional considerations included the complexities of merger-related purchase accounting, potential asset sales to reduce CRE concentration, treatment of First Foundation’s capital instruments (including preferred stock and warrants), runoff of higher-cost and non-core funding, and opportunities for organic loan growth. No specific proposal regarding price, ownership split or other transaction terms was made by either party. Both Mr. Shafer and Mr. Arnold agreed that the potential merger warranted further evaluation, and each committed to reviewing next steps, including the execution of non-disclosure agreements, and sharing observations with their respective boards of directors.

On March 19, 2025, Mr. Shafer participated in an introductory call with the CEO of another bank, which was coordinated by Jefferies Group LLC (“Jefferies”). Following the discussion, both parties determined that they were not interested in pursuing further conversations.

On March 25, 2025, Mr. Shafer discussed with members of the First Foundation board of directors a preliminary merger concept between First Foundation and FirstSun. He summarized his conversations with Mr. Arnold and conveyed FirstSun’s potential interest in exploring a strategic combination. Mr. Shafer outlined the potential benefits of such a merger, including the creation of a premium commercial bank with greater asset size and scale and the opportunity to deliver improved stockholder value for both institutions. Key advantages discussed included diversification into a more balanced commercial bank and loan mix, improved funding sources, materially stronger performance metrics than First Foundation was likely to achieve on a standalone basis, enhancements to First Foundation’s wealth management platform, and a branch network spanning Southern California, Arizona, New Mexico, Texas, Florida and Colorado—regions viewed as attractive growth markets. Mr. Shafer also noted FirstSun’s strong operating track record, successful history of merger integration, and its ability to contribute robust earnings and significant excess capital to the combined entity. The board of First Foundation also considered potential risks, including transaction timing and process, historical discussions between the two companies that did not result in a transaction, implications of FirstSun’s withdrawal of its merger application to acquire HomeStreet in November 2024 for publicly-disclosed regulatory reasons, and the operational complexities of integrating the two organizations. Mr. Shafer expressed his belief that the merger could accelerate actions that would be appropriate to improve First Foundation’s operating performance with lower execution risk, achieving long-term objectives within one to two years rather than the three- to five-year timeline anticipated on a standalone basis. After deliberation, the board authorized management to continue exploring the potential merger through preliminary diligence, subject to evaluation of major execution impediments and transaction assumptions, and to report back with more detailed findings at the April 29 board meeting.

On April 29, 2025, at a meeting of the First Foundation board of directors, representatives of KBW provided the board and management with a preliminary overview of the potential combination of First Foundation and FirstSun. The discussion focused on the strategic rationale for the merger, including a range of potential financial impacts, and preliminary assumptions. Critical diligence topics were also discussed. The board discussed FirstSun’s likely regulatory standing, the current regulatory environment, and considerations for optimizing the combined balance sheet, such as selling non-relationship loans and reducing large wholesale deposits. The board also discussed the need for third-party loan reviews for both institutions, the feasibility and desirability of the projected financial impacts, contributions by each entity, the prevailing interest rate environment, and preliminary timetables for diligence and evaluation of critical items.

Both companies continued to share information and decided to reconvene in May for more detailed work sessions covering topics such as earnings forecasts, potential synergies, fair value assumptions, regulatory readiness for a merger, credit reviews, information technology compatibility, and enterprise risk management systems. Information was also shared through a virtual data room accessible to both parties. On May 1, 2025, FirstSun and First Foundation entered into a mutual confidentiality agreement, which also included a reciprocal non-solicitation covenant relating to employees and customers, but did not include any standstill obligation, in anticipation of those discussions.

On May 8, 2025, Mr. Arnold, Mr. Cafera, and Mr. Shafer met in person in Detroit, Michigan to further discuss the potential of a proposed merger of their respective companies. Beginning on May 8, 2025, and continuing through May 24, 2025, representatives of First Foundation, FirstSun, KBW, and Stephens held multiple in-person and virtual meetings to facilitate mutual information sharing and advance the companies’ diligence efforts.

From May 28 through May 30, 2025, members of the First Foundation board of directors met with members of the First Foundation senior management team and representatives of KBW to conduct a strategic review and receive an update on a potential merger with FirstSun. KBW provided an overview of the banking market, the California banking landscape, financial matters relating to First Foundation, selected bank merger and acquisition transactions, and potential strategic options, including possible acquirers for First Foundation based on publicly available information regarding their financial capacity and potential willingness to transact, as well as KBW’s familiarity with such other possible acquirers. Transaction alternatives discussed included a strategic merger with a similarly-sized entity, a control sale to a larger institution, the acquisition of a smaller bank, and branch acquisitions. The First Foundation board of directors considered the potential for enhancing stockholder value and the execution risks associated with each alternative. Specific matters identified included the size of fair value marks, the dilutive impact of First Foundation’s preferred stock and warrants, and risks within the wealth management unit. The discussion also addressed inquiries received by Mr. Shafer in recent weeks from various parties, either directly or through investment bankers. These inquiries contemplated transaction structures from reverse takeovers by smaller banks to control sales to larger entities. After preliminary dialogue, the board concluded that the nature of these inquiries was either unlikely to result in an attractive outcome for First Foundation stockholders or would require further diligence, which would result in significant costs for First Foundation and consume substantial internal and external resources. Moreover, the board recognized that First Foundation did not have the necessary time to undertake such extensive diligence given First Foundation’s current circumstances, the regulatory climate, and strategic priorities. The First Foundation board of directors also deliberated on the benefits and risks of pursuing a negotiated merger versus conducting an auction or multiparty process to identify additional interested parties and determined that conducting an auction process would likely deter FirstSun, which appeared to remain the strongest contender for a strategic transaction. The board additionally discussed: First Foundation’s prospects as a standalone entity; its ability to achieve target performance levels; necessary improvements to the CECL framework, loan concentrations and deposit mix; under-scaled products and commercial lending capabilities; risk factors within and beyond management’s control; and the timeline for improving net interest margin and earnings. Further discussion regarding a potential merger with FirstSun included a review of prior diligence sessions, the size and scope of fair value marks, potential balance sheet optimization, improvements in loan mix and deposit composition, reductions in wholesale funding reliance, branch locations in growth markets, the potential earnings power of the combined entity, preliminary valuation considerations, and transaction assumptions.

A preliminary timeline for a potential merger with FirstSun was discussed. The First Foundation board of directors authorized management to continue considering the possibility of a merger with FirstSun, while also remaining open to other strategic approaches, and to further evaluate any inquiries received for potential viability. The First Foundation board of directors also determined that forming an ad hoc board-level working group (the “M&A Working Group”) – comprised of certain members of the First Foundation board of directors and senior management – to be available for Mr. Shafer and the First Foundation management team and advisors in exploring potential transactions and further negotiations would be beneficial. Accordingly, the M&A Working Group was established, which would meet to discuss key negotiation points and to report back to the full board of directors to ensure fully informed, Board-level decision-making regarding a potential transaction with FirstSun, as well as any proposed terms thereof.

In early June 2025, in accordance with input and direction from the First Foundation board, Mr. Shafer and a KBW representative engaged in follow-up conversations with three bank CEOs during a KBW-hosted, multi-day CEO-only conference. Each CEO had previously expressed some level of strategic interest in First Foundation. Through these discussions, two CEOs concluded that the scope of a potential transaction and related integration challenges were such that no further dialogue was warranted. The third CEO, however, expressed interest in exploring a potential transaction, which the parties agreed would require additional evaluation and discussion.

Additionally, in June 2025, Mr. Shafer participated in introductory telephone meetings with the CEOs of two additional banks. These meetings were coordinated by Jefferies. Following the discussions, neither First Foundation nor the other parties expressed interest in pursuing further conversations.

Throughout June and early July 2025, Mr. Shafer and a KBW representative responded to an inquiry from a bank with less than $500 million in assets. The inquiring bank conveyed confidence in its ability to structure a market-premium cash transaction supported by strong financial resources; however, no formal capital commitments had been made at the time of these discussions. A series of discussions revealed that the proposed structure would require First Foundation to sell control in a take-private transaction, with First Foundation stockholders electing either cash or exchanging their shares for equity in a privately held combined entity. The proposal contemplated asset sales upon closing, treatment of First Foundation as the purchase accounting target (subject to fair value adjustments) and raising the necessary funds to appropriately capitalize the combined entity following announcement of the transaction. On July 10, 2025, at a meeting of the First Foundation board of directors, KBW reviewed the inquiring bank’s proposal and facilitated discussion regarding the value proposition, execution risks, strategic implications and conditions to proceeding, including exclusivity and regulatory considerations. After deliberating on the potential impact to stockholders and other stakeholders, the board determined that pursuing the proposal was not in the best interests of First Foundation stockholders.

During late June and through mid-July 2025, senior management of First Foundation and FirstSun, with assistance from KBW and Stephens, continued joint work sessions to assess the viability of a potential merger between First Foundation and FirstSun. During this process, FirstSun expressed the need to reach a mutual understanding regarding steps that could be taken to optimize the combined entity’s balance sheet to focus more on relationship-based lending and funding. This optimization would involve selling approximately $3 billion of wholesale, non-relationship loans and securities and repaying a similar amount of wholesale, non-relationship deposits and liabilities. The M&A Working Group participated closely in the consideration of these matters. On July 22, 2025, Mr. Shafer and Mr. Arnold, supported by KBW and Stephens, jointly presented a detailed balance sheet optimization assessment to the First Foundation board. The discussion addressed the anticipated impacts on the combined entity, including key performance metrics, earnings, capital ratios, regulatory ratios and liquidity, as well as the foregone benefits associated with downsizing and the risks of execution. The board also reviewed comparative analyses of post-optimization versus no-optimization scenarios.

Over the following days, members of the First Foundation board of directors, with assistance from First Foundation’s senior management and advisors, continued evaluating the impacts of the proposed balance sheet optimization. They also authorized continuation of discussions and acknowledged that FirstSun intended to share a preliminary analysis, including the optimization plan, with the OCC. The First Foundation board of directors emphasized the need for both parties to pursue a more specific preliminary non-binding letter of interest (“LOI”) that included a defined value proposition, rather than the illustrative ranges of value and ownership previously discussed. By early August, Mr. Arnold indicated that a range of ownership split between approximately 40% and 41% would likely represent FirstSun’s limit on ownership granted to holders of First Foundation stock (assuming cashless exercise of the outstanding warrants to acquire First Foundation stock). However, significant work remained to address volatility in First Foundation’s earnings under various interest rate scenarios. Over the next 10 days, First Foundation senior management, with assistance from KBW, refined its analysis for inclusion in a joint package to be shared by FirstSun with the OCC (FirstSun’s primary bank regulator) and the FDIC (First Foundation’s primary bank regulator).

On August 12, 2025, FirstSun’s board of directors met in an executive session to discuss the proposed transaction with FirstSun management and representatives from Stephens and Nelson Mullins. During this executive session, the board discussed the status of merger and acquisition activity within the banking sector and FirstSun’s regional growth in the Southern California market. Mr. Arnold, Mr. Cafera and representatives from Stephens provided a presentation to the board regarding FirstSun’s position in the market and potential merger opportunities, and specifically, a potential merger with First Foundation. The board discussed the strategic, regulatory and organizational aspects of a proposed merger with First Foundation, and the board supported FirstSun management and Stephens continuing discussions in pursuit of a potential merger with First Foundation.

On August 14, 2025, Mr. Shafer and representatives from KBW met with the CEO and CFO of a substantially larger banking institution to discuss the potential acquisition of First Foundation by that entity. The illustrative transaction was presented as potentially beneficial to both stockholder groups by delivering strong returns, expanding market share, adding new logical markets, accelerating key performance metrics, providing durable earnings accretion, preserving cultural alignment, generating material synergies, and posing limited regulatory concerns. The concept also contemplated repositioning a portion of the acquiring entity’s loan assets to strengthen the combined balance sheet and overall performance. After several days of subsequent dialogue and review, the larger institution determined that it would not be willing to proceed with a transaction with First Foundation.

On August 21, 2025, following its review of the diligence materials provided to it by First Foundation, FirstSun submitted a draft non-binding term sheet to First Foundation, to outline some of the material terms regarding its proposed acquisition of First Foundation, including terms related to the form of the merger consideration and ownership split, transaction structure, board governance, and other terms that would be used to structure a definitive agreement between the parties. Following discussions between legal and financial advisors for the parties, FirstSun submitted a revised draft non-binding term sheet to First Foundation on August 25, 2025. In late August and early September, senior management teams of First Foundation and FirstSun, along with their respective advisors, met on multiple occasions to further develop the non-binding term sheet and a letter of intent and continue work on the ownership split between First Foundation and FirstSun stockholders. Significant time and analysis were devoted to earnings forecasts under various interest rate scenarios, given the potential impact of different rate environments on each institution’s financial performance. Following these discussions and analysis, FirstSun submitted a further revised draft non-binding term sheet to First Foundation on September 9, 2025.

During the September 11, 2025 board meeting of First Foundation, the First Foundation board of directors determined to formally establish a M&A Committee—comprised of the same members of the M&A Working Group—authorized by the board to continue negotiations with FirstSun and to report back to the full board on a regular basis; however, the M&A Committee would not have authority to execute a non-binding LOI, or to commit to any terms, without a vote of the full First Foundation board of directors. The board additionally discussed certain items that they wished to raise to FirstSun with respect to the preliminary term sheet and approved the M&A Committee to present a counterproposal to the preliminary term sheet addressing those items.

Between September 11 and 15, 2025, the M&A Committee of First Foundation’s board met three times with senior management and outside advisors to review the status of discussions and negotiations with FirstSun and other potential counterparties. During these meetings, the M&A Committee first focused on FirstSun’s term sheet, particularly the proposed ownership split, governance arrangements, lock-up provisions, and mechanisms for ownership adjustment at closing, and reviewed financial analyses addressing earnings impact, tangible book value, accretion metrics, and sensitivity scenarios under varying interest rate environments. After addressing ownership and related governance matters the Committee turned to discussing warrant treatment options, including FirstSun’s insistence on terminating the outstanding warrants through a cashless exercise with a proposed $10 million termination fee payable to warrant holders, as well as alternative approaches such as assumption of warrants and Black-Scholes option valuation modeling. After deliberation, the M&A Committee agreed on proposed revisions for the next draft of the term sheet, prioritizing an increase in First Foundation’s pro forma ownership, seeking reciprocal lock-up commitments, and recommending an increase in the warrant termination fee to $25 million to better align with valuation analyses of the various warrant holders. The M&A Committee also discussed regulatory approval considerations, accounting implications and fiduciary duties, emphasizing transparency and First Foundation stockholder interests throughout its deliberations. The M&A Committee agreed to continue refining terms and due diligence and to convene a full board meeting to review the transaction status and proposed revisions before providing further feedback to FirstSun.

On September 16, 2025, the First Foundation board of directors met with senior management and outside advisors to review and direct First Foundation’s negotiation of drafts of the mutually developed LOI with FirstSun. Several key terms remained under negotiation, including the ownership split (ranging from 40.0% to 42.0%), conditions related to a minimum fully converted tangible common equity test at closing, treatment of outstanding warrants, lock-up agreement provisions, and other material terms. In addition, the full board considered items raised by the M&A Committee, including the implications of exchange ratio adjustments, warrant valuation and termination alternatives, and possible reciprocal lock-up commitments, all with a focus on ensuring alignment with stockholder interests and that the board was negotiating in the best interests of First Foundation stockholders. The board reviewed proposed counter provisions submitted to FirstSun and FirstSun’s responses, including clarifications on regulatory conditions and lock-up timing, and evaluated scenario analyses comparing positions under different interest rate environments and warrant treatment options, as well as anticipated third-quarter earnings disclosures and their potential impact. Additional discussion focused on internal and external factors affecting the minimum tangible common equity test and potential operational actions. The board also considered the M&A Committee’s proposed term sheet revisions, including a $25 million warrant termination payment not tied to the minimum tangible common equity test, clarifications on inclusions and exclusions to the capital test and use of VWAP for cashless exercise valuation. The board discussed the strategic upside of the merger versus the risks of remaining a standalone company, FirstSun’s unwillingness to accept certain counterproposals, and alternatives available to First Foundation if FirstSun declined the revised terms, including in light of ongoing performance challenges. The meeting concluded with an in-depth discussion of tangible common equity metrics and the financial, regulatory, and operational challenges facing First Foundation as a standalone entity. Following the meeting of the full board, the independent directors not nominated by the bank’s private equity investors conferred with outside counsel regarding ongoing negotiations with FirstSun and reviewed the term sheet and related proposals. They expressed their support of the full board’s position and its decision to proceed with presenting the discussed terms to FirstSun.

On September 18, 2025, FirstSun delivered its “best and final” LOI, proposing an all-stock merger and setting forth exclusivity terms and an expiration date. The LOI contemplated 100% stock consideration, with First Foundation stockholders expected to own approximately 40.5% of the combined company at closing, assuming full conversion of outstanding equity instruments. The LOI addressed treatment of outstanding warrants through a combination of cashless exercise and a termination payment of $17.5 million and included provisions requiring agreement on minimum tangible common equity levels and balance sheet optimization measures prior to signing a definitive agreement. The exchange ratio would be fixed, with no collars or adjustments, and FirstSun would be the legal and accounting acquirer. Governance terms included a proposed 13-member board, with eight directors designated by FirstSun and five by First Foundation, and certain senior management continuing in their roles post-merger. The LOI did not contemplate any new employment or change in control agreements with executives of First Foundation. The LOI also contemplated voting and lock-up agreements for significant First Foundation stockholders, customary representations and warranties, regulatory approvals, and standard termination rights, including a mutual break-up fee.

Following delivery of the September 18, 2025 LOI, the M&A Committee met with senior management and outside advisors to review the LOI. The Committee discussed key terms, including exchange ratio mechanics, anticipated cost synergies, integration planning, and forward-looking projections comparing First Foundation’s standalone outlook to the proposed combination. Scenario analyses were presented to illustrate potential outcomes under varying market conditions, and the M&A Committee deliberated on procedural steps required to accept or reject the LOI. The M&A Committee also considered broader macroeconomic and regulatory factors that could impact the transaction. Following these discussions, the M&A Committee recommended that the full First Foundation board of directors carefully review the LOI and consider the M&A Committee’s observations and flagged items—such as ownership structure, warrant treatment, lock-up provisions and financial implications—before determining next steps. After thorough consideration of the M&A Committee’s considerations and after receiving advice and input from the First Foundation management team, members of the M&A Committee, and outside advisors, the First Foundation board unanimously decided to approve the LOI, and the LOI was fully executed on September 18, 2025.

Beginning September 24, 2025, First Foundation and FirstSun initiated a series of joint diligence meetings covering financial reporting, audit, asset/liability management, credit, deposit operations, legal and regulatory matters, information technology, enterprise risk management, wealth management operations, synergy and cost analysis, refined fair value assessments, balance sheet optimization impacts, and hedging strategies. Both institutions engaged internal teams and external subject matter experts to support these due diligence efforts. On October 9, 2025, the M&A Committee received an update on diligence progress and optimization planning, including potential provisions in the merger agreement or a side letter addressing each respective entity’s obligations with respect to mutually agreed expenses. Mr. Shafer outlined the anticipated timeline, noting that diligence was expected to conclude by mid-October and that key meetings, including a full board review of the merger agreement, had been scheduled. The M&A Committee also discussed coordination on outstanding matters, including a comprehensive review of the WETA with the full board of directors, and concluded that one-time charges were unlikely to affect minimum tangible common equity or impede deal completion.

On October 1, 2025, Nelson Mullins delivered the initial draft of the merger agreement to Alston & Bird. Negotiations of the merger agreement focused on reciprocal representations and warranties, expense reimbursement obligations, ownership threshold protections, and governance and closing mechanics. Negotiations also addressed regulatory covenants, termination rights and fiduciary considerations to align the agreement with market standards and best practices. On October 7, 2025, Nelson Mullins circulated the first draft of the WETA and Lock-Up Agreement, initiating negotiations centered on the economic terms for warrant holders. Certain of the largest warrant holders each hired outside counsel that were heavily involved in the negotiation of the WETA, the Lock-Up Agreement, and the board representation letters. Over the course of the following weeks, the parties and their respective legal advisors negotiated the principal terms of the merger agreement and related transaction documents, including the WETA, Lock-Up Agreement, board representation letters and Support Agreements. In particular the parties worked through due diligence matters requiring resolution prior to execution of a definitive agreement, discussed the treatment of First Foundation’s warrants, preferred stock and equity-based compensation awards and related benefit plans, and negotiated the terms of representations and warranties for both sides, covenants for both sides and termination rights and fees. In addition, each party prepared drafts of disclosure schedules listing certain supplemental information and exceptions to the representations and warranties contained in the merger agreement. While negotiating the definitive merger agreement, the parties and their representatives continued to conduct ongoing, reciprocal comprehensive due diligence regarding the business, operations and markets of the other party.

On October 13, 2025, the M&A Committee met to review the draft merger agreement and emphasized the importance of involving the full board of directors in discussions. Topics included post-closing governance, merger structure, board representation, merger consideration, treatment of equity awards, and closing conditions such as the no-shop covenant. The Committee discussed open issues, including the definition of minimum tangible common equity, board recommendations and fiduciary outs, termination rights, regulatory conditions, interim conduct provisions, reciprocal representations and warranties, and ancillary agreements such as the WETA, Lock-Up Agreement and Support Agreements. Updates on due diligence indicated no material issues that would prevent the transaction. On October 21, 2025, the M&A Committee reconvened to continue governance discussions and receive a diligence update. By October 22, 2025, the full First Foundation board of directors met with senior management to review diligence findings, including a third-party credit review of FirstSun’s loan portfolio, and the First Foundation board of directors and senior management concluded there were no material issues preventing the merger from proceeding.

On October 24, 2025, the First Foundation board of directors held a special meeting to consider the proposed final terms of the merger agreement with FirstSun. Members of management and representatives from Alston & Bird, KBW, and Jefferies (which represented First Foundation in connection with the recapitalization transaction in 2024, and which was engaged to provide a fairness opinion in connection with the FirstSun transaction) attended and presented materials prepared for the meeting. The First Foundation board of directors reviewed the provisions of the merger agreement and the related ancillary agreements, discussed employee matters and received advice from Alston & Bird regarding directors’ fiduciary duties. KBW and Jefferies each provided a preliminary review of their respective financial analyses and advised that, assuming no material changes, they would each be prepared to deliver a fairness opinion at signing, which was subsequently provided by each of KBW on October 26, 2025 and Jefferies on October 25, 2025. After discussion, the First Foundation board of directors approved, through three separate actions (with appropriate recusals)—by the full board, by the independent directors, and by the non-private-equity affiliated directors—the merger agreement and the transactions contemplated thereby and authorized the continued negotiation of the final open items in the merger agreement.

Similarly, on October 24, 2025, FirstSun’s board of directors held a meeting to discuss the proposed transaction and to review due diligence and the substantially complete terms of the merger agreement. Mr. Arnold provided an overview of the process that led to the transaction. Representatives of Nelson Mullins reviewed in detail the terms of the merger agreement and the ancillary agreements, including the WETA, Lock-Up Agreement and Support Agreements. Management next reported to the board the detailed results of FirstSun’s due diligence investigation of First Foundation. Further, representatives of Stephens reviewed with the board of directors its analysis of the financial terms contained in the merger agreement, including the balance sheet re-positioning strategy and the expected financial benefits of the transaction. The board discussed the advantages and rationales for proceeding with the transaction.

Because certain key aspects of the merger agreement were still under negotiation between First Foundation and FirstSun, including provisions related to balance sheet optimization, hedging strategies, and First Foundation’s limited expense reimbursement, the First Foundation board of directors convened again on October 26, 2025, to review updates and differences from its prior discussion on October 24. After considering these revisions and related side letter provisions, the board unanimously approved the merger agreement, ancillary agreements, and the transactions contemplated thereby.

On October 27, 2025, FirstSun’s board of directors reconvened and held a meeting to discuss the proposed transaction and the final terms of the merger agreement. Representatives from Nelson Mullins reviewed the terms of the merger agreement that had been finalized since the board’s previous review of the merger agreement on October 24, 2025. Additionally, representatives of Stephens reviewed with the board of directors its analysis of the updated financial terms of the merger. Additionally, Stephens delivered its oral opinion, which was confirmed in writing on October 27, 2025, to the effect that, as of such date and subject to the procedures followed, assumptions made, matters considered, and qualifications and limitations on the review undertaken by Stephens as set forth in its opinion, the consideration to be given by FirstSun in the proposed merger was fair to FirstSun from a financial point of view. After further discussion among the directors and FirstSun’s advisors, including with respect to the factors described in “FirstSun’s Reasons for the Merger”, FirstSun’s board of directors unanimously determined that it was in the best interests of FirstSun’s stockholders to proceed with the transaction on the terms provided in the merger agreement and thereafter, the board unanimously approved the merger agreement and the issuance of shares as a part of the merger consideration as contemplated in the merger agreement. Representatives of FirstSun reported the board’s actions to First Foundation’s representatives following the meeting.

FirstSun and First Foundation executed the merger agreement on October 27, 2025. The transaction was subsequently announced on October 27, 2025 after the closing of the financial markets in New York, in a press release jointly issued by FirstSun and First Foundation.

FirstSun’s Reasons for the Merger

After careful consideration, the FirstSun board of directors, at a special meeting held on October 27, 2025, based upon the information provided to the board and upon such other matters as were deemed relevant by the board, unanimously (a) determined that the merger agreement and the transactions (including the merger and the share issuances) are fair and in the best interests of FirstSun and its stockholders and declared it advisable for FirstSun to enter into the merger agreement, (b) adopted and approved the merger agreement and (c) authorized and approved the execution, delivery and performance of the merger agreement and the transactions contemplated thereby, including the merger.

In reaching this decision, the FirstSun board of directors carefully evaluated the merger agreement, the merger, the bank merger and the other matters contemplated by the merger agreement, in consultation with FirstSun’s senior management, and FirstSun’s legal counsel and financial advisor, and considered a number of factors, including the following principal factors:

The FirstSun board of directors also considered potential risks related to the merger. The FirstSun board of directors concluded that the anticipated benefits of combining with First Foundation were likely to outweigh these risks. These potential risks include:

The foregoing discussion of the information and factors considered by the FirstSun board of directors is not intended to be exhaustive but includes the material factors considered by the FirstSun board of directors in reaching its unanimous decision to adopt and approve the merger agreement and the transactions contemplated thereby, including the merger. In reaching its decision to approve the merger agreement and the transactions contemplated thereby, including the merger, the FirstSun board of directors did not quantify or assign any relative weights to the factors considered, and individual directors may have given different weights to different factors. The FirstSun board of directors considered all these factors as a whole, including through its discussions with FirstSun’s management and financial and legal advisors, in evaluating the merger agreement and the transactions contemplated thereby, including the merger.

There can be no assurance about future results, including results expected or considered in the factors listed above. This explanation of the reasoning of the FirstSun board of directors and all other information presented in this section is forward- looking in nature and, therefore, should be read in light of the future factors discussed in the section entitled “Cautionary Statement Regarding Forward-Looking Statements.” The FirstSun board of directors unanimously concluded that the potential positive factors outweighed the potential risks of completing the merger.

In considering the recommendation of the FirstSun board of directors, you should be aware that certain directors and executive officers of FirstSun may have interests in the merger that are different from, or in addition to, interests of FirstSun stockholders generally and may create potential conflicts of interest. The FirstSun board of directors was aware of these interests and considered them when evaluating and negotiating the merger agreement, the merger and the other transactions contemplated by the merger agreement, and in unanimously recommending to FirstSun stockholders that they vote in favor of the FirstSun merger proposal.

For the reasons set forth above, the FirstSun board of directors unanimously determined that the merger was fair to, advisable and in the best interests of FirstSun and its stockholders and unanimously adopted and approved the merger agreement and the transactions contemplated thereby, including the merger and the bank merger (which was also approved by the board of directors of Sunflower Bank, National Association in a joint board capacity with the FirstSun board of directors) and entry into the merger agreement by FirstSun. The FirstSun board of directors recommends that FirstSun stockholders vote “FOR” the FirstSun merger proposal, “FOR” the FirstSun authorized common stock increase proposal, “FOR” the FirstSun non-voting common stock proposal, and “FOR” the FirstSun adjournment proposal.

First Foundation’s Reasons for the Merger

After careful consideration, the First Foundation board of directors unanimously (i) determined that the merger agreement and the transactions contemplated thereby, including the merger, are in the best interests of First Foundation and its stockholders, (ii) declared the merger agreement advisable and (iii) approved the execution, delivery and performance of the merger agreement and the consummation of the transactions contemplated thereby, including the merger. Accordingly, the First Foundation board of directors unanimously recommends that First Foundation common stockholders vote FOR approval of the First Foundation merger proposal, FOR approval of the First Foundation merger compensation proposal, FOR approval of the First Foundation adjournment proposal and FOR approval of the First Foundation amendment proposal.

In reaching its decision to approve the merger agreement and the transactions contemplated thereby, including the merger, and to recommend that First Foundation common stockholders adopt the merger agreement, the First Foundation board of directors consulted with First Foundation management, as well as First Foundation’s financial and legal advisors, and considered a number of factors, including the following:

This discussion of the information and factors considered by First Foundation’s board of directors in reaching its conclusions and recommendation includes principal factors considered by the board of directors but is not intended to be exhaustive and may not include all of the factors considered by the First Foundation board of directors. In view of the wide variety of factors considered in connection with its evaluation of the merger and the other transactions contemplated by the merger agreement, and the complexity of these matters, the First Foundation board of directors did not find it useful and did not attempt to quantify, rank or assign any relative or specific weights to the various factors that it considered in reaching its determination to approve the merger and the other transactions contemplated by the merger agreement, and to make its recommendation to First Foundation stockholders. Rather, the First Foundation board of directors viewed its decisions as being based on the totality of the information presented to it and the factors it considered. In addition, individual members of the First Foundation board of directors may have assigned different weights to different factors.

Certain of First Foundation’s directors and executive officers have other interests in the merger that are different from, or in addition to, those of First Foundation’s stockholders generally, as discussed under the caption “—Interests of First Foundation Directors and Executive Officers in the Merger” below. The First Foundation board of directors was aware of and considered these potential interests, among other matters, in evaluating the merger and in making its recommendation to First Foundation stockholders.

Certain Unaudited Prospective Financial Information

FirstSun and First Foundation do not, as a matter of course, publicly disclose forecasts or internal projections as to their respective future performance, financial condition, revenues, earnings or other results, due to, among other reasons, the inherent uncertainty of the underlying assumptions and estimates.

However, in connection with the merger, FirstSun senior management and First Foundation senior management prepared or approved for use certain unaudited prospective financial information that was provided to and considered by Stephens, as financial advisor to FirstSun, and by KBW and Jefferies, as financial advisors to First Foundation, for the purpose of performing financial analyses in connection with their respective opinions, as described in this joint proxy statement/prospectus under “—Opinion of FirstSun’s Financial Advisor” and “—Opinions of First Foundation’s Financial Advisors,” including the contemplated balance sheet repositioning and whether it has the expected effects. We refer to this information collectively as the “prospective financial information.”

The prospective financial information was not prepared for the purpose of, or with a view toward, public disclosure or with a view toward complying with the guidelines established by the American Institute of Certified Public Accountants for preparation and presentation of prospective financial information, published guidelines of the SEC regarding forward-looking statements, or generally accepted accounting principles (“GAAP”). A summary of certain significant elements of this information is set forth below and is included in this joint proxy statement/prospectus solely to provide holders of First Foundation common stock and FirstSun common stock access to certain nonpublic information made available to the respective financial advisors for purposes of their opinions.

Although presented with numeric specificity, the prospective financial information reflects numerous estimates and assumptions made by FirstSun senior management or First Foundation senior management, as applicable, at the time such prospective financial information was prepared or approved for use and represents management’s respective evaluation of expected future financial performance on a stand-alone basis, without giving effect to the merger. These and other estimates and assumptions involve judgments with respect to, among other things, economic, competitive, regulatory and financial market conditions and future business decisions that may not be realized and that are inherently subject to significant business, economic, competitive and regulatory uncertainties and contingencies, many of which are outside the control of FirstSun and First Foundation. There can be no assurance that the underlying assumptions will prove to be accurate or that the projected results will be realized, and actual results could differ materially from those reflected in the prospective financial information, whether or not the merger is completed.

Further, these assumptions do not include all potential actions that the senior management of FirstSun or First Foundation could or might take during these periods. The inclusion of the unaudited prospective financial information in this joint proxy statement/prospectus should not be regarded as an indication that FirstSun, First Foundation, or their respective boards of directors, or their financial advisors, considered—or now consider—this prospective financial information to be material information to holders of either company’s common stock, particularly in light of the inherent risks and uncertainties associated with such information. The prospective financial information is not fact and should not be relied upon as being necessarily indicative of actual future results.

The prospective financial information also reflects numerous variables, expectations and assumptions available at the time it was prepared as to certain business decisions that are subject to change and does not take into account any circumstances or events occurring after the date it was prepared. No assurances can be given that if the prospective financial information and the underlying assumptions had been prepared as of the date of this joint proxy statement/prospectus, similar assumptions would be used. In addition, the prospective financial information may not reflect the manner in which the combined company will operate after the merger.

The prospective financial information included in this document has been prepared by, and is the responsibility of, the management of FirstSun and First Foundation, as applicable. Crowe LLP, FirstSun’s and First Foundation’s independent registered public accounting firm, has not audited, reviewed, examined, compiled or applied agreed-upon procedures with respect to the prospective financial information and, accordingly, Crowe LLP has expressed no opinion and provided no form of assurance with respect thereto and assumes no responsibility for it. The reports of Crowe LLP incorporated by reference in this joint proxy statement/prospectus relate solely to the historical audited financial statements of FirstSun and First Foundation, respectively, and do not extend to the prospective financial information.

In light of the foregoing and taking into account that the First Foundation special meeting and the FirstSun special meeting will be held several months after the prospective financial information was prepared, as well as the uncertainties inherent in any forecasted information, stockholders are strongly cautioned not to place unwarranted reliance on such information.

FirstSun Prospective Financial Information

Stephens. In performing its financial analysis with respect to FirstSun on a standalone basis, Stephens used the following prospective financial information regarding FirstSun: (i) estimated earnings per share for FirstSun of $1.70 for the period from July 1, 2025 to December 31, 2025, $0.88 for the period from January 1, 2026 to March 31, 2026, $3.68 for the year ending December 31, 2026, $4.01 for the year ending December 31, 2027, $4.31 for the year ending December 31, 2028, $4.60 for the year ending December 31, 2029, and $4.91 for the year ending December 31, 2030; and (ii) an estimated annual earnings per share and balance sheet growth rate thereafter through the year ending December 31, 2030 of 7.0%.

The following table presents certain unaudited prospective financial information regarding FirstSun on a stand-alone basis from July 1, 2025 through December 31, 2030, which Stephens used in connection with developing its financial analyses and fairness opinion.

*The difference between Stephens’ projected 2026 earnings per share of $3.68 and the $3.69 figure used by KBW and Jefferies reflects a difference in calculation approach. EPS used by Stephens was based on a spot share count as of December 31, 2026 (the actual number of shares at year-end), while EPS used by KBW and Jefferies was based on an average share count for the year (a blended number across all of 2026). 

The foregoing prospective financial information regarding FirstSun was provided to Stephens by the management team of FirstSun and was approved by FirstSun for Stephens’ use and reliance in connection with developing its financial analyses and fairness opinion.

KBW. In certain of the financial analyses performed by KBW in connection with its opinion, KBW utilized financial forecasts and projections provided by FirstSun management. The following presents certain unaudited prospective financial information regarding FirstSun on a stand-alone basis, including a long-term growth rate, provided to and utilized by KBW.

LT Earnings and Asset Growth (2031)        7.0%

The foregoing prospective financial information regarding FirstSun was provided to KBW by the management team of FirstSun and was approved by First Foundation for KBW’s use and reliance in performing financial analyses in connection with its opinion.

Jefferies. In performing its financial analysis with respect to FirstSun on a standalone basis, Jefferies used the following prospective financial information regarding FirstSun: (i) estimated earnings per share for FirstSun of $1.70 for the period from July 1, 2025 to December 31, 2025, $0.88 for the period from January 1, 2026 to March 31, 2026, $3.69 for the year ending December 31, 2026, $4.01 for the year ending December 31, 2027, $4.31 for the year ending December 31, 2028, $4.60 for the year ending December 31, 2029, and $4.91 for the year ending December 31, 2030; and (ii) an estimated annual earnings per share and balance sheet growth rate thereafter through the year ending December 31, 2030 of 7.0%.

The following table presents certain unaudited prospective financial information regarding FirstSun on a stand-alone basis from July 1, 2025 through December 31, 2030, which Jefferies used in connection with developing its financial analyses and fairness opinion. 

The foregoing prospective financial information regarding FirstSun was provided to Jefferies by the management team of FirstSun and was approved by First Foundation for Jefferies’ use and reliance in connection with developing its financial analyses and fairness opinion.

First Foundation Prospective Financial Information

Stephens. In performing its financial analysis with respect to First Foundation on a standalone basis, Stephens used the following prospective financial information regarding First Foundation: (i) estimated earnings per share for First Foundation of ($1.77) for the period from July 1, 2025 to December 31, 2025, $0.03 for the period from January 1, 2026 to March 31, 2026, $0.20 for the year ending December 31, 2026, $0.30 for the year ending December 31, 2027, $0.34 for the year ending December 31, 2028, $0.36 for the year ending December 31, 2029, and $0.37 for the year ending December 31, 2030.

The following table presents certain unaudited prospective financial information regarding First Foundation on a stand- alone basis from July 1, 2025 through December 31, 2030, which Stephens used in connection with developing its financial analyses and fairness opinion.

The foregoing prospective financial information regarding First Foundation was developed by the management team of FirstSun based on internal estimates and information provided to FirstSun by First Foundation. Such prospective financial information was provided by the management team of FirstSun to Stephens and was approved by FirstSun for Stephens’ use and reliance in connection with developing its financial analyses and fairness opinion, and reflects the impact of the balance sheet repositioning.

KBW. In certain of the financial analyses performed by KBW in connection with its opinion, KBW utilized financial forecasts and projections provided by First Foundation management. The following presents certain unaudited prospective financial information regarding First Foundation on a stand-alone basis, including certain long-term growth rates, provided to and utilized by KBW.

The foregoing prospective financial information regarding First Foundation was provided to KBW by the management team of First Foundation and was approved by First Foundation for KBW’s use and reliance in performing financial analyses in connection with its opinion. The foregoing prospective financial information does not reflect the impact of the balance sheet repositioning.

Jefferies. In performing its financial analysis with respect to First Foundation on a standalone basis, Jefferies used the following prospective financial information regarding First Foundation: (i) estimated earnings per share for First Foundation of ($1.29) for the period from July 1, 2025 to December 31, 2025, $0.00 for the period from January 1, 2026 to March 31, 2026, $0.36 for the year ending December 31, 2026, $0.63 for the year ending December 31, 2027, $0.70 for the year ending December 21, 2028, $0.77 for the year ending December 31, 2029, and $0.84 for the year ending December 31, 2030, and (ii) an estimated annual earnings per share growth rate of 10% and loan, securities, and other asset growth of 3% and deposit growth of 2% thereafter through the year ending December 31, 2030.

The following table presents certain unaudited prospective financial information regarding First Foundation on a stand- alone basis from July 1, 2025 through December 31, 2030, which Jefferies used in connection with developing its financial analyses and fairness opinion.

The foregoing prospective financial information regarding First Foundation provided to Jefferies by the management team of First Foundation and was approved by First Foundation for Jefferies’ use and reliance in connection with developing its financial analyses and fairness opinion.

Estimated Synergies Attributable to the Merger

The management team of FirstSun developed and provided to its boards of directors prospective financial information relating to the anticipated strategic, financial and operational benefits to, and synergies estimated to be realized following the completion of the proposed merger beginning in 2025. Such prospective financial information also was provided by the management team of FirstSun to Stephens and was approved by FirstSun for Stephens’ use and reliance in connection with Stephens’ financial analyses and fairness opinion as described in this joint proxy statement/prospectus under “—Opinion of FirstSun’s Financial Advisor”.

Such prospective financial information included, among other things, (i) annual pre-tax cost savings of approximately 35% of First Foundation’s noninterest expense, after-tax, phased in 66% during 2026 and 100% thereafter; (ii) one-time, pre-tax cash transaction costs of $95 million, which were fully reflected in tangible book value at the completion of the proposed merger; and (iii) estimated purchase accounting adjustments. The prospective financial information assumed a hypothetical March 31, 2026 closing date for the proposed merger.

Opinion of FirstSun’s Financial Advisor

On October 24, 2025, FirstSun engaged Stephens to act as financial advisor to FirstSun in connection with the proposed merger of First Foundation with and into FirstSun. As part of its engagement, Stephens was asked to undertake a study of the fairness, from a financial point of view, of the consideration to be given by FirstSun in connection with the proposed merger. FirstSun engaged Stephens because, among other factors, Stephens is a nationally recognized investment banking firm with substantial experience in similar transactions. As part of its investment banking business, Stephens is continually engaged in the valuation of financial services businesses and their securities in connection with mergers and acquisitions.

As part of Stephens’ engagement, representatives of Stephens participated in a meeting of FirstSun’s board of directors held on October 27, 2025, in which FirstSun’s board of directors considered and approved the proposed merger. At this meeting, Stephens reviewed the financial aspects of the proposed merger and rendered its oral opinion, which was subsequently confirmed by delivery of a written opinion to FirstSun’s board of directors dated as of October 27, 2025, that, as of such date, the consideration to be given by FirstSun in the proposed merger was fair to FirstSun from a financial point of view, based upon and subject to the qualifications, assumptions and other matters considered by Stephens in connection with the preparation of its opinion.

The full text of Stephens’ written opinion letter (the “Opinion Letter”) is attached as Annex B to this joint proxy statement/prospectus. The Opinion Letter outlines the procedures followed, assumptions made, matters considered and qualifications and limitations on the review undertaken by Stephens in rendering its opinion.

The summary of the opinion set forth in this document is qualified in its entirety by reference to the full text of such written Opinion Letter. Investors are urged to read the entire Opinion Letter carefully in connection with their consideration of the proposed merger. FirstSun did not give any instruction to or impose any limitations on Stephens as it related to the issuance of its opinion.

Stephens’ opinion speaks only as of the date of the opinion, and Stephens has undertaken no obligation to update or revise its opinion. The opinion was directed to FirstSun’s board of directors (solely in its capacity as such) in connection with, and for purposes of, its consideration of the proposed merger. The opinion only addresses whether the consideration to be given by FirstSun in the proposed merger was fair to FirstSun from a financial point of view as of the date of the opinion. The opinion does not address the underlying business decision of FirstSun to engage in the proposed merger or any other term or aspect of the merger agreement or the transactions contemplated thereby. Stephens’ opinion does not constitute a recommendation to FirstSun’s board of directors or any of FirstSun’s stockholders as to how such person should vote or otherwise act with respect to the proposed merger or any other matter. FirstSun and First Foundation determined the merger consideration through a negotiation process.

In connection with developing its opinion, Stephens:

Stephens relied on the accuracy and completeness of the information, financial data and financial forecasts provided to Stephens by FirstSun and First Foundation and of the other information reviewed by Stephens in connection with the preparation of Stephens’ opinion, and its opinion was based upon such information. Stephens did not independently verify or undertake any responsibility to independently verify the accuracy or completeness of any of such information, data or forecasts. Management of FirstSun and management of First Foundation assured Stephens that they were not aware of any relevant information that had been omitted or remained undisclosed to Stephens. Stephens did not assume any responsibility for making or undertaking an independent evaluation or appraisal of any of the assets or liabilities of FirstSun or of First Foundation, and Stephens was not furnished with any such evaluations or appraisals; nor did Stephens evaluate the solvency or fair value of FirstSun or of First Foundation under any laws relating to bankruptcy, insolvency or similar matters. Stephens did not assume any obligation to conduct any physical inspection of the properties, facilities, assets or liabilities (contingent or otherwise) of FirstSun or First Foundation. Stephens did not receive or review any individual loan or credit files nor did Stephens make an independent evaluation of the adequacy of the allowance for credit losses of FirstSun or First Foundation.

Stephens did not make an independent analysis of the effects of potential future changes in the rate of inflation or of prevailing rates of interest or other market developments or disruptions, or of the effects of any global conflicts or hostilities or any other disaster or adversity, on the business or prospects of FirstSun or First Foundation. With respect to the financial projections or forecasts prepared by management of FirstSun and management of First Foundation, including the forecasts of potential cost savings and potential synergies, Stephens also assumed that such financial projections or forecasts had been reasonably prepared and reflected the best then currently available estimates and judgments of management of FirstSun and management of First Foundation, respectively, as to the future financial performance of FirstSun and First Foundation, respectively, and provided a reasonable basis for Stephens’ analysis. Stephens recognized that such financial projections or forecasts were based on numerous variables, assumptions and judgments that were inherently uncertain (including, without limitation, factors related to general economic and competitive conditions) and that actual results could vary significantly from such projections or forecasts, and Stephens expressed no opinion as to the reliability of such financial projections, forecasts or estimates or the assumptions upon which they were based.

Stephens does not provide legal, accounting, regulatory, or tax advice or expertise, and Stephens relied solely, and without independent verification, on the assessments of FirstSun and its other advisors with respect to such matters. Stephens assumed, with FirstSun’s consent, that the proposed merger will not result in any materially adverse legal, regulatory, accounting or tax consequences for FirstSun and that any reviews of legal, accounting, regulatory or tax issues conducted as a result of the proposed merger will be resolved favorably to FirstSun. Stephens did not express any opinion as to any tax or other consequences that might result from the proposed merger.

Stephens’ opinion was necessarily based upon market, economic and other conditions as they existed and could be evaluated on the date of the opinion, and on the information made available to Stephens as of the date of the opinion. Market price data used by Stephens in connection with its opinion was based on reported market closing prices as of October 24, 2025. It should be understood that subsequent developments may affect the opinion and that Stephens did not undertake any obligation to update, revise or reaffirm the opinion or otherwise comment on events occurring after the date of the opinion. Stephens further noted that volatility or disruptions in the credit and financial markets relating to, among other things, potential future changes in the rate of inflation or prevailing rates of interest or other market developments or disruptions, or the effects of any global conflicts or hostilities, or any other disaster or adversity may or may not have an effect on FirstSun or First Foundation, and Stephens did not express an opinion as to the effects of such volatility or disruptions on the proposed merger or any party to the proposed merger. Stephens further expressed no opinion as to the prices at which shares of First Foundation’s or FirstSun’s common stock may trade at any time subsequent to the announcement of the proposed merger.

In connection with developing its opinion, Stephens assumed that, in all respects material to its analyses:

Stephens’ opinion was limited to whether the consideration to be given by FirstSun in the proposed merger was fair to FirstSun from a financial point of view as of the date of the opinion. Stephens was not asked to, and it did not, offer any opinion as to the terms of the merger agreement or the form of the proposed merger or any aspect of the proposed merger, other than the fairness, from a financial point of view, of the consideration to be given in the proposed merger by FirstSun. The opinion did not address the merits of the underlying decision by FirstSun to engage in the proposed merger, the merits of the proposed merger as compared to other alternatives potentially available to FirstSun or the relative effects of any alternative transaction in which FirstSun might engage, nor is it intended to be a recommendation to any person or entity as to any specific action that should be taken in connection with the proposed merger, including with respect to how to vote or act with respect to the proposed merger. Moreover, Stephens did not express any opinion as to the fairness of the amount or nature of the compensation to any of FirstSun’s officers, directors or employees, or to any group of such officers, directors or employees, whether relative to the compensation to other stockholders of FirstSun or otherwise.

The following is a summary of the material financial analyses performed and material factors considered by Stephens in connection with developing its opinion. In performing the financial analyses described below, Stephens relied on the financial and operating data, projections and other financial information and assumptions concerning FirstSun and First Foundation provided by management of FirstSun and management of First Foundation, as applicable, and Stephens reviewed with FirstSun’s executive management and board of directors certain assumptions concerning FirstSun and First Foundation upon which the analyses were based, as well as other factors. Although this summary does not purport to describe all of the analyses performed or factors considered by Stephens, it does set forth those analyses considered by Stephens to be material in arriving at its opinion. The preparation of a fairness opinion is a complex analytical process involving various determinations as to the appropriate and relevant methods of financial analysis and the application of those methods to the particular circumstances. Therefore, a fairness opinion is not readily susceptible to partial analysis or summary description. The order of the summaries of analyses described does not represent the relative importance or weight given to those analyses by Stephens. It should be noted that in arriving at its opinion, Stephens did not attribute any particular weight to any analysis or factor considered by it, but rather made qualitative judgments as to the significance and relevance of each analysis and factor.

Accordingly, Stephens believes that its analysis must be considered as a whole and that considering any portion of such analyses and factors, without considering all analyses and factors as a whole, could create a misleading or incomplete view of the process underlying its opinion. The financial analyses summarized below include information presented in tabular format. The tables alone do not constitute a complete description of the financial analyses summarized below. Accordingly, Stephens’ analyses and the summary of its analyses must be considered as a whole and selecting portions of its analyses and factors or focusing on the information presented below in tabular format, without considering all analyses and factors or the full narrative description of the financial analyses, including the methodologies and assumptions underlying the analyses, could create a misleading or incomplete view of the process underlying Stephens’ analyses and opinion.

Summary of Proposed Merger

Pursuant to the merger agreement, and subject to the terms, conditions and limitations set forth therein, and for purposes of its opinion, Stephens understood that, subject to potential adjustments as described in the merger agreement, the aggregate consideration expected to be paid by FirstSun for all of the outstanding equity interests of First Foundation (including common stock, restricted stock, preferred stock and warrants) has an aggregate value of approximately $784.3 million as of November 30, 2025, based upon FirstSun’s closing stock price of $40.44 on October 24, 2025.

The consideration is expected to consist of (i) the issuance of 0.16083 shares of FirstSun’s common stock for each outstanding share of First Foundation’s common stock (including restricted stock, preferred stock and stock issued upon the exercise of outstanding warrants), and (ii) an aggregate cash payment of $17.5 million to holders of outstanding warrants. Based upon the unaudited financial information of the First Foundation as of and for the twelve months ended June 30, 2025 and September 30, 2025, and market data as of October 24, 2025, Stephens calculated the following transaction multiples:

Public Market Evaluation

Relevant Public Companies Analysis – First Foundation

Stephens compared the financial condition, operating statistics and market valuation of First Foundation to certain public companies selected by Stephens and their respective public trading values. Stephens selected the companies outlined below because their relative asset size and financial performance, among other factors, were reasonably similar to First Foundation; however, no selected company below was identical or directly comparable to First Foundation. A complete analysis involves complex considerations and qualitative judgments concerning differences in financial and operating characteristics and other factors that could affect the public trading values of the relevant public companies. Mathematical analysis (such as determining the median) is not in itself a meaningful method of using relevant public company data.

Stephens selected the following public companies based on the criteria set forth below:

Nationwide major exchange-traded (NASDAQCM, NASDAQGM, NASDAQGS, NYSE, and NYSEAM) banks with 2025Q2 total assets between $6.5 billion and $30.0 billion and 2025Q2 Core ROAA (per S&P Global Market Intelligence) less than 0.85%, excluding non-traditional business models (LOB and WASH), ethnic-focused banks (HAFC, HOPE and FFIC), merger targets, merger-of-equals participants (as defined by S&P Global Market Intelligence) and mutuals:

To perform this analysis, Stephens reviewed publicly available financial information as of and for the last twelve month period ended June 30, 2025, or the most recently reported period available, and the market trading multiples of the selected public companies based on October 24, 2025 closing prices. The financial data included in the table presented below may not correspond precisely to the data reported in historical financial statements as a result of the assumptions and methods used by Stephens to compute the financial data presented. The table below contains information reviewed and utilized by Stephens in its analysis: