FOR IMMEDIATE RELEASE

PROSPERITY BANCSHARES, INC.®

REPORTS THIRD QUARTER

2025 EARNINGS

HOUSTON, October 29, 2025. Prosperity Bancshares, Inc.® (NYSE: PB) (“Prosperity Bancshares”), the parent company of Prosperity Bank® (collectively, “Prosperity”), reported net income of $137.6 million for the quarter ended September 30, 2025, compared with $127.3 million for the same period in 2024. Net income per diluted common share was $1.45 for the quarter ended September 30, 2025, compared with $1.34 for the same period in 2024. The annualized return on third quarter average assets was 1.44%. Additionally, deposits increased $308.7 million during the third quarter of 2025. Nonperforming assets remain low at 0.36% of third quarter average interest-earning assets.

“In the third quarter we signed a definitive merger agreement with Southwest Bancshares, Inc., the parent company of Texas Partners Bank, headquartered in San Antonio, Texas. We are excited about this transaction as it significantly expands our San Antonio metro footprint with 4 additional branches and increased deposit market share, bolsters our presence in the Texas Hill Country and adds an experienced C&I lending team,” said David Zalman, Prosperity’s Senior Chairman and Chief Executive Officer.

“I would also be remiss not to mention how excited we are about our pending merger with American Bank Holding Corporation in Corpus Christi, Texas. The combination will strengthen our presence and operations in South Texas and surrounding areas and enhance our presence in Central Texas, including San Antonio,” continued Zalman.

“I am also pleased to announce that the Board of Directors approved increasing the fourth quarter 2025 dividend to $0.60 per share from $0.58 per share that was paid in the prior four quarters. The increase reflects the continued confidence the Board has in our company and our markets. The compound annual growth rate in dividends declared from 2003 to 2025 was 10.7%. We continue to share our success with our shareholders through the payment of dividends and opportunistic stock repurchases, while also continuing to grow our capital,” stated Zalman.

“As of October 2025, Texas boasts one of the world's strongest and most diverse economies, ranking as the 8th largest globally with a GDP of approximately $2.77 trillion in 2024. The state produces about 9.3% of U.S. GDP and continues to outpace national growth in many metrics. Although the economy is showing some signs of moderation, influenced by factors such as tariffs and immigration policies, we believe Texas remains the best state for business with a pro-business attitude and no state income tax. This is evidenced by major corporations continuing to move their operations to Texas and Oklahoma,” added Zalman.

“As of October 2025, Oklahoma's economy is demonstrating resilience and modest growth, outpacing national averages in key areas such as unemployment and population expansion despite broader U.S. slowdowns from tariffs and policy uncertainties,” continued Zalman.

“I would like to thank our customers, associates, directors and shareholders for their hard work and loyalty. Our fundamentals and resolve have never been stronger to continue to build this successful company,” concluded Zalman.

Results of Operations for the Three Months Ended September 30, 2025

Net income was $137.6 million(2) for the three months ended September 30, 2025, compared with $127.3 million(3) for the same period in 2024, an increase of $10.3 million or 8.1%. Net income per diluted common share was $1.45 for the three months ended September 30, 2025, compared with $1.34 for the same period in 2024, an increase of 8.2%. The changes were primarily due to an increase in net interest income, partially offset by an increase in provision for income taxes. On a linked quarter basis, net income was $137.6 million(2) for the three months ended September 30, 2025, compared with $135.2 million(4) for the three months ended June 30, 2025, an increase of $2.4 million or 1.8%. Net income per diluted common share was $1.45 for the three months ended September 30, 2025, compared with $1.42 for the three months ended June 30, 2025. Annualized returns on average assets, average common equity and average tangible common equity for the three months ended September 30, 2025, were 1.44%, 7.18% and 13.43%(1), respectively. Prosperity’s efficiency ratio (excluding net gains and losses on the sale, write-down or write-up of assets and securities) was 44.06%(1) for the three months ended September 30, 2025.

Net interest income before provision for credit losses was $273.4 million for the three months ended September 30, 2025, compared with $261.7 million for the same period in 2024, an increase of $11.7 million or 4.5%. The change was primarily due to a decrease in the average balances and average rates on other borrowings and a decrease in the average rates on interest-bearing deposits, partially offset by a decrease in the average balances and average rates on federal funds sold and other earning assets, a decrease in the average balances and average rates on loans and a decrease in loan discount accretion of $2.0 million. Net interest income before provision for credit losses increased $5.7 million or 2.1% to $273.4 million for the three months ended September 30, 2025, compared with $267.7 million for the three months ended June 30, 2025, primarily due to one extra day during the current quarter and a decrease in the average balances for other borrowings.

The net interest margin on a tax equivalent basis was 3.24% for the three months ended September 30, 2025, compared with 2.95% for the same period in 2024. The change was primarily due to a decrease in the average balances and average rates on other borrowings and a decrease in the average rates on interest-bearing deposits, partially offset by a decrease in the average balances and average rates

on federal funds sold and other earning assets, a decrease in the average balances and average rates on loans and a decrease in loan discount accretion of $2.0 million. The net interest margin on a tax equivalent basis was 3.24% for the three months ended September 30, 2025, compared with 3.18% for the three months ended June 30, 2025, primarily due to a decrease in the average balances for other borrowings.

Noninterest income was $41.2 million for the three months ended September 30, 2025, compared with $41.1 million for the same period in 2024. Noninterest income was $41.2 million for the three months ended September 30, 2025, compared with $43.0 million for the three months ended June 30, 2025, a decrease of $1.7 million. The change was primarily due to a decrease in net gain on sale or write-down of assets.

Noninterest expense was $138.6 million for the three months ended September 30, 2025, compared with $140.3 million for the same period in 2024, a decrease of $1.7 million, primarily due to a decrease in other noninterest expense. Noninterest expense was $138.6 million for the three months ended September 30, 2025, and the three months ended June 30, 2025.

Results of Operations for the Nine Months Ended September 30, 2025

For the nine months ended September 30, 2025, net income was $402.9 million(5) compared with $349.3 million(6) for the same period in 2024, an increase of $53.6 million or 15.4%. Net income per diluted common share was $4.23 for the nine months ended September 30, 2025, compared with $3.68 for the same period in 2024, an increase of 14.9%. The changes were primarily due to an increase in net interest income, lower merger related provision and expenses, and lower regulatory assessments and FDIC insurance, partially offset by a decrease in net gain on sale or write-up of securities. Returns on average assets, average common equity and average tangible common equity for the nine months ended September 30, 2025, were 1.40%, 7.08% and 13.36%(1), respectively.

Net interest income before provision for credit losses for the nine months ended September 30, 2025, was $806.5 million compared with $758.7 million for the same period in 2024, an increase of $47.8 million or 6.3%. The change was primarily due to a decrease in the average balances and average rates on other borrowings and a decrease in the average rates on interest-bearing deposits, partially offset by a decrease in the average balances on investment securities, a decrease in the average balances and average rates on federal funds sold and other earning assets, a decrease in loan discount accretion of $4.6 million and a decrease in the average balances on loans.

The net interest margin on a tax equivalent basis for the nine months ended September 30, 2025, was 3.19% compared with 2.86% for the same period in 2024. The change was primarily due to a decrease in the average balances and average rates on other borrowings and a decrease in the average rates on interest-bearing deposits, partially offset by a decrease in the average balances on investment securities, a decrease in the average balances and average rates on federal funds sold and other earning assets, a decrease in loan discount accretion of $4.6 million and a decrease in the average balances on loans.

Noninterest income was $125.5 million for the nine months ended September 30, 2025, compared with $126.0 million for the same period in 2024.

Noninterest expense was $417.5 million for the nine months ended September 30, 2025, compared with $429.0 million for the same period in 2024, a decrease of $11.5 million or 2.7%, primarily due to decreases in regulatory assessment and FDIC insurance, merger related expenses and other noninterest expense.

Balance Sheet Information

Prosperity had $38.330 billion in total assets at September 30, 2025, compared with $38.417 billion at June 30, 2025, and $40.115 billion at September 30, 2024. The decrease was primarily due to the reduction in borrowings by $1.50 billion from September 30, 2024 to September 30, 2025.

Loans were $22.028 billion at September 30, 2025, a decrease of $169.6 million from $22.197 billion at June 30, 2025. Loans decreased $353.1 million from $22.381 billion at September 30, 2024.

Loans, excluding Warehouse Purchase Program loans, were $20.750 billion at September 30, 2025, compared with $20.910 billion at June 30, 2025, a decrease of $160.4 million, and compared with $21.152 billion at September 30, 2024, a decrease of $402.6 million.

Deposits were $27.782 billion at September 30, 2025, an increase of $308.7 million or 1.1% from $27.473 billion at June 30, 2025. Deposits decreased $305.5 million from $28.088 billion at September 30, 2024.

Asset Quality

Nonperforming assets totaled $119.6 million or 0.36% of quarterly average interest-earning assets at September 30, 2025, compared with $110.5 million or 0.33% of quarterly average interest-earning assets at June 30, 2025, and $89.9 million or 0.25% of quarterly average interest-earning assets at September 30, 2024, with a significant portion of the balance for each period attributable to acquired loans.

The allowance for credit losses on loans and off-balance sheet credit exposures was $377.3 million at September 30, 2025, compared with $383.7 million at June 30, 2025, and $392.0 million at September 30, 2024. There was no provision for credit losses for the three and nine months ended September 30, 2025, compared to no provision for credit losses for the three months ended September 30, 2024, and a $9.1 million provision for credit losses for the nine months ended September 30, 2024.

The allowance for credit losses on loans was $339.6 million or 1.54% of total loans at September 30, 2025, compared with $346.1 million or 1.56% of total loans at June 30, 2025, and $354.4 million or 1.58% of total loans at September 30, 2024. Excluding Warehouse Purchase Program loans, the allowance for credit losses on loans to total loans was 1.64%(1) at September 30, 2025, compared with 1.66%(1) at June 30, 2025, and 1.68%(1) at September 30, 2024.

Net charge-offs were $6.5 million for the three months ended September 30, 2025, compared with net charge-offs of $3.0 million for the three months ended June 30, 2025, and net charge-offs of $5.5 million for the three months ended September 30, 2024. For the three months ended September 30, 2025, $4.5 million of reserves on resolved purchased credit deteriorated (“PCD”) loans without any related charge-offs were released to the general reserve.

Net charge-offs were $12.2 million for the nine months ended September 30, 2025, compared with net charge-offs of $12.0 million for the nine months ended September 30, 2024. For the nine months ended September 30, 2025, $15.0 million of reserves on resolved PCD loans without any related charge-offs were released to the general reserve.

Dividend

Prosperity Bancshares declared a fourth quarter 2025 cash dividend of $0.60 per share to be paid on January 2, 2026, to all shareholders of record as of December 15, 2025, an increase of $0.02 per share, or 3.45%, from the prior quarter.

Stock Repurchase Program

On January 21, 2025, Prosperity Bancshares announced a stock repurchase program under which up to 5%, or approximately 4.8 million shares, of its outstanding common stock may be acquired over a one-year period expiring on January 21, 2026, at the discretion of management. Under its 2025 stock repurchase program, Prosperity Bancshares repurchased 299,318 shares of its common stock at an average weighted price of $66.62 per share during the three and nine months ended September 30, 2025.

Agreement to Acquire Southwest Bancshares, Inc.

On October 1, 2025, Prosperity Bancshares and Southwest Bancshares, Inc. (“Southwest) jointly announced the signing of a definitive merger agreement (the “Prosperity/Southwest Merger Agreement”) whereby Southwest, a Texas corporation and bank holding company of Texas Partners Bank (“Texas Partners”), will merge with and into Prosperity Bancshares and Texas Partners will merge with and into Prosperity Bank. Texas Partners operates 11 banking offices in Central Texas including its main office in San Antonio, and banking offices in the San Antonio area, Austin and the Hill Country. As of June 30, 2025, Southwest, on a consolidated basis, reported total assets of $2.354 billion, total loans of $1.890 billion and total deposits of $2.129 billion.

Under the terms and subject to the conditions of the Prosperity/Southwest Merger Agreement, Prosperity Bancshares will issue 4,062,520 shares of Prosperity Bancshares common stock for all outstanding shares of Southwest common stock and restricted stock awards, subject to certain potential adjustments. Southwest warrants and in-the-money Southwest stock options that are outstanding at the closing will be converted into cash payments based on the value of the merger consideration (less the applicable exercise price), as calculated pursuant to the terms of the Prosperity/Southwest Merger Agreement. Based on Prosperity Bancshares’s closing price of $65.97 on September 29, 2025, the total consideration was valued at approximately $268.9 million. The transaction is subject to customary closing conditions, including the receipt of regulatory approvals and approval by the shareholders of Southwest. The transaction is expected to close during the first quarter of 2026.

Pending Acquisition of American Bank Holding Corporation

On July 18, 2025, Prosperity Bancshares and American Bank Holding Corporation (“American”) jointly announced the signing of a definitive merger agreement (the “Prosperity/American Merger Agreement”) whereby American, a Texas corporation and bank holding company of American Bank, N.A. (“American Bank”), will merge with and into Prosperity Bancshares and American Bank will merge with and into Prosperity Bank. American Bank operates 18 banking offices and 2 loan production offices in South and Central Texas including its main office in Corpus Christi, and banking offices in San Antonio, Austin, Victoria and the greater Corpus Christi area including Port Aransas and Rockport and a loan production office in Houston, Texas. As of June 30, 2025, American, on a consolidated basis, reported total assets of $2.553 billion, total loans of $1.798 billion and total deposits of $2.293 billion.

Under the terms and subject to the conditions of the Prosperity/American Merger Agreement, Prosperity Bancshares will issue 4,439,981 shares of Prosperity Bancshares common stock for all outstanding shares of American common stock, subject to certain potential adjustments. Based on Prosperity Bancshares’ closing price of $72.40 on July 16, 2025, the total consideration was valued at approximately $321.5 million. The transaction is subject to customary closing conditions, including the receipt of required regulatory approvals and approval of the shareholders of American. The transaction is expected to close during the fourth quarter of 2025 or the first quarter of 2026.

Conference Call

Prosperity’s management team will host a conference call on Wednesday, October 29, 2025, at 11:30 a.m. Eastern Time (10:30 a.m. Central Time) to discuss Prosperity’s third quarter 2025 earnings. Individuals and investment professionals may participate in the call by dialing 877-883-0383 for domestic participants, or 412-902-6506 for international participants. The participant elite entry number is 2818776.

Alternatively, individuals may listen to the live webcast of the presentation by visiting Prosperity’s website at www.prosperitybankusa.com. The webcast may be accessed from Prosperity’s Investor Relations page by selecting “Presentations, Webcasts & Calls” from the menu and following the instructions.

Non-GAAP Financial Measures

Prosperity’s management uses certain non-GAAP financial measures to evaluate its performance. Specifically, for internal planning and forecasting purposes, Prosperity reviews each of diluted earnings per share, return on average assets, return on average common equity, and return on average tangible common equity, in each case excluding merger related provision for credit losses, net of tax, merger related expenses, net of tax, Federal Deposit Insurance Corporation (“FDIC”) special assessment, net of tax, and net gain on the sale or write-up of securities, net of tax; return on average tangible common equity; tangible book value per share; the tangible equity to tangible assets ratio; allowance for credit losses to total loans excluding Warehouse Purchase Program loans; the efficiency ratio, excluding net gains and losses on the sale, write-down or write-up of assets and securities; and the efficiency ratio, excluding net gains and losses on the sale, write-down or write-up of assets and securities, merger related expenses, and FDIC special assessment. Prosperity believes these non-GAAP financial measures provide information useful to investors in understanding Prosperity’s financial results and their presentation, together with the accompanying reconciliations, provides a more complete understanding of factors and trends affecting Prosperity’s business and allows investors to view performance in a manner similar to management, the entire financial services sector, bank stock analysts and bank regulators. Further, Prosperity believes that these non-GAAP financial measures provide useful information by excluding certain items that may not be indicative of its core operating earnings and business outlook. These non-GAAP financial measures should not be considered a substitute for, nor of greater importance than, GAAP basis financial measures and results; Prosperity strongly encourages investors to review its consolidated financial statements in their entirety and not to rely on any single financial measure. Because non-GAAP financial measures are not standardized, it may not be possible to compare these financial measures with other companies’ non-GAAP financial measures having the same or similar names. Please refer to the “Notes to Selected Financial Data” at the end of this Earnings Release for a reconciliation of these non-GAAP financial measures to the nearest respective GAAP financial measures.

Prosperity Bancshares, Inc. ®

As of September 30, 2025, Prosperity Bancshares, Inc.® is a $38.330 billion Houston, Texas based regional financial holding company providing personal banking services and investments to consumers and businesses throughout Texas and Oklahoma. Founded in 1983, Prosperity believes in a community banking philosophy, taking care of customers, businesses and communities in the areas it serves by providing financial solutions to simplify everyday financial needs. In addition to offering traditional deposit and loan products, Prosperity offers digital banking solutions, credit and debit cards, mortgage services, retail brokerage services, trust and wealth management, and treasury management.

Prosperity currently operates 283 full-service banking locations: 62 in the Houston area, including The Woodlands; 33 in the South Texas area including Corpus Christi and Victoria; 61 in the Dallas/Fort Worth area; 22 in the East Texas area; 31 in the Central Texas area including Austin and San Antonio; 45 in the West Texas area including Lubbock, Midland-Odessa, Abilene, Amarillo and Wichita Falls; 15 in the Bryan/College Station area; 6 in the Central Oklahoma area; and 8 in the Tulsa, Oklahoma area.

Cautionary Notes on Forward-Looking Statements

“Safe Harbor” Statement under the Private Securities Litigation Reform Act of 1995: This release contains, and the remarks by Prosperity’s management on the conference call may contain, statements regarding the proposed transactions between (1) Prosperity Bancshares, Inc. (“Prosperity”) and Southwest Bancshares, Inc. (“Southwest”) and (2) Prosperity and American Bank Holding Corporation (“American”); future financial and operating results; benefits and synergies of the transactions; future opportunities for Prosperity; the issuances of common stock of Prosperity contemplated by the Agreement and Plan of Merger by and between Prosperity and Southwest (the “Prosperity/Southwest Merger Agreement”) and the Agreement and Plan of Merger by and between Prosperity and American (the “Prosperity/American Merger Agreement” and, together with the Prosperity/Southwest Merger Agreement, the “Merger Agreements”); in connection with the proposed transaction between Prosperity and Southwest, the expected filing by Prosperity with the Securities and Exchange Commission (the “SEC”) of a registration statement on Form S-4 (the “Prosperity/Southwest Registration Statement”) and a prospectus of Prosperity and a proxy statement of Southwest to be included therein (the “Prosperity/Southwest Proxy Statement/Prospectus”); in connection with the proposed transaction between Prosperity and American, a registration statement on Form S-4 (the “Prosperity/American Registration Statement” and, together with the Prosperity/Southwest Registration Statement, the “Registration Statements”) and a preliminary prospectus of Prosperity and a proxy statement of American included therein (the “Prosperity/American Proxy Statement/ Prospectus” and, together with the Southwest Proxy Statement/ Prospectus, the “Proxy Statement/ Prospectuses”), which registration statement was filed with the SEC on September 17, 2025, and amended on September 30, 2025; the expected timing of the closing of the proposed transactions; the ability of the parties to complete the proposed transactions considering the various closing conditions and any other statements about future expectations that constitute forward-looking statements within the meaning of the federal securities laws, including the meaning of the Private Securities Litigation Reform Act of 1995, as amended, Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended. From time to time, oral or written forward-looking statements may also be included in other information released to the public. Such forward-looking statements are typically, but not exclusively, identified by the use in the statements of words or phrases such as “aim,” “anticipate,” “believe,” “estimate,” “expect,” “goal,” “guidance,” “intend,” “is anticipated,” “is expected,” “is intended,” “objective,” “plan,” “projected,” “projection,” “will affect,” “will be,” “will continue,” “will decrease,” “will grow,” “will impact,” “will increase,” “will incur,” “will reduce,” “will remain,” “will result,” “would be,” variations of such words or phrases (including where the word “could,” “may,” or “would” is used rather than the word “will” in a phrase) and similar words and phrases indicating that the statement addresses some future result, occurrence, plan or objective. Forward-looking statements include all statements other than statements of historical fact, including forecasts or trends, and are based on current expectations, assumptions, estimates, and projections about Prosperity and its subsidiaries or related to the proposed transactions between (1) Prosperity and Southwest and (2) Prosperity and American and are subject to significant risks and uncertainties that could cause actual results to differ materially from the results expressed in such statements.

These forward-looking statements may include information about Prosperity’s possible or assumed future economic performance or future results of operations, including future revenues, income, expenses, provision for credit losses, provision for taxes, effective tax rate, earnings per share and cash flows and Prosperity’s future capital expenditures and dividends, future financial condition and changes therein, including changes in Prosperity’s loan portfolio and allowance for credit losses, future capital structure or changes therein, as well as the plans and objectives of management for Prosperity’s future operations, future or proposed acquisitions, the future or expected effect of acquisitions on Prosperity’s operations, results of operations, financial condition, and future economic performance, statements about the anticipated benefits of each of the proposed transactions, and statements about the assumptions underlying any such statement.

These forward-looking statements are not guarantees of future performance and are based on expectations and assumptions Prosperity currently believes to be valid. Because forward-looking statements relate to future results and occurrences, many of which are outside of Prosperity’s control, they are subject to inherent uncertainties, risks and changes in circumstances that are difficult to predict. These risks and uncertainties include, but are not limited to, whether Prosperity can: successfully identify acquisition targets and integrate the businesses of acquired companies and banks; continue to sustain its current internal growth rate or total growth rate; provide products and services that appeal to its customers; continue to have access to debt and equity capital markets; and achieve its sales objectives. Other risks include, but are not limited to: the possibility that credit quality could deteriorate; actions of competitors; changes in laws and regulations (including changes in governmental interpretations of regulations and changes in accounting standards); a deterioration or downgrade in the credit quality and credit agency ratings of the securities in Prosperity’s securities portfolio; customer and consumer demand, including customer and consumer response to marketing; effectiveness of spending, investments or programs; fluctuations in the cost and availability of supply chain resources; economic conditions, including currency rate, interest rate and commodity price fluctuations; changes in trade policies by the United States or other countries, such as tariffs or retaliatory tariffs; and

the effect, impact, potential duration or other implications of weather and climate-related events. Many possible events or factors could adversely affect the future financial results and performance of Prosperity, Southwest or American or the combined company and could cause those results or performance to differ materially from those expressed in or implied by the forward-looking statements. Such risks and uncertainties include, among others: (1) the risk that the cost savings and synergies from the transactions may not be fully realized or may take longer than anticipated to be realized, (2) disruption to Prosperity’s, Southwest’s and American’s businesses as a result of the announcements and pendency of the transactions, (3) the risk that the integration of Southwest’s and/or American’s businesses and operations into Prosperity, will be materially delayed or will be more costly or difficult than expected, or that Prosperity is otherwise unable to successfully integrate Southwest’s and/or American’s business into its own, including as a result of unexpected factors or events, (4) the failure to obtain the necessary approval by the shareholders of Southwest and/or American, (5) the ability by each of Prosperity, Southwest and/or American to obtain required governmental approvals of the transactions on the timeline expected, or at all, and the risk that such approvals may result in the imposition of conditions that could adversely affect Prosperity after the closing of the transactions or adversely affect the expected benefits of the transactions, (6) reputational risk and the reaction of each company’s customers, suppliers, employees or other business partners to the transactions, (7) the failure of the closing conditions in the applicable Merger Agreements to be satisfied, or any unexpected delay in closing the transactions or the occurrence of any event, change or other circumstances that could give rise to the termination of the applicable Merger Agreements, (8) the dilution caused by the issuances of additional shares of Prosperity’s common stock in the transactions, (9) the possibility that the transactions may be more expensive to complete than anticipated, including as a result of unexpected factors or events, (10) the outcome of any legal or regulatory proceedings that may be currently pending or later instituted against Prosperity before or after any of the transactions, or against Southwest or American, (11) diversion of management’s attention from ongoing business operations and (12) general competitive, economic, political and market conditions and other factors that may affect future results of Prosperity, Southwest and American. Prosperity disclaims any obligation to update such factors or to publicly announce the results of any revisions to any of the forward-looking statements included herein to reflect future events or developments. These and various other factors are discussed in Prosperity’s Annual Report on Form 10-K, Quarterly Reports on Form 10- Q, and Current Reports on Form 8-K, in each case filed with the SEC, and other reports and statements Prosperity has filed with the SEC. Copies of the SEC filings for Prosperity may be downloaded from the Internet at no charge from http://www.prosperitybankusa.com.

Additional Information about the Transactions and Where to Find It

Prosperity intends to file with the SEC the Prosperity/Southwest Registration Statement on Form S-4 to register the shares of Prosperity common stock to be issued to the shareholders of Southwest in connection with Prosperity’s and Southwest’s proposed transaction. The Prosperity/Southwest Registration Statement will include the Prosperity/Southwest Proxy Statement/Prospectus which will be sent to the shareholders of Southwest in connection with the proposed transaction. This communication is not a substitute for the Prosperity/Southwest Proxy Statement/Prospectus or any other document which Prosperity may file with the SEC. In connection with Prosperity’s and American’s proposed transaction, Prosperity has filed with the SEC on September 17, 2025 the Prosperity/American Registration Statement on Form S-4, as amended on September 30, 2025, (the “Amended Prosperity/American Registration Statement”) (which Amended Prosperity/American Registration Statement was declared effective by the SEC on September 30, 2025), to register the shares of Prosperity common stock to be issued to the shareholders of American in connection with Prosperity’s and American’s proposed transaction. The Prosperity/American Proxy Statement/Prospectus will be delivered to shareholders of American. Prosperity may also file other documents with the SEC regarding the proposed transaction. This communication is not a substitute for the Prosperity/American Proxy Statement/Prospectus or Amended Prosperity/American Registration Statement or any other document which Prosperity may file with the SEC. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE APPLICABLE REGISTRATION STATEMENT ON FORM S-4, THE APPLICABLE PROXY STATEMENT/PROSPECTUS INCLUDED WITHIN THE APPLICABLE REGISTRATION STATEMENT ON FORM S-4 AND ANY OTHER RELEVANT DOCUMENTS TO BE FILED WITH THE SEC IN CONNECTION WITH THE PROPOSED TRANSACTIONS OR INCORPORATED BY REFERENCE INTO THE APPLICABLE PROXY/STATEMENT PROSPECTUS, AS WELL AS ANY AMENDMENTS OR SUPPLEMENTS TO THESE DOCUMENTS, CAREFULLY AND IN THEIR ENTIRETY, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT PROSPERITY, SOUTHWEST, AMERICAN AND THE APPLICABLE PROPOSED TRANSACTIONS. Investors and security holders may obtain free copies of these documents through the website maintained by the SEC at http://www.sec.gov. You will also be able to obtain these documents, free of charge, from Prosperity at http://www.prosperitybankusa.com. Copies of the Prosperity/American Proxy Statement/Prospectus (and the Prosperity/Southwest Proxy Statement/Prospectus, when it becomes available), can also be obtained, free of charge, by directing a request by telephone or mail to Prosperity Bancshares, Inc., Prosperity Bank Plaza, 4295 San Felipe, Houston, Texas 77027 Attn: Investor Relations, (281) 269-7199, or with respect to the Prosperity/American Proxy Statement/Prospectus, to American Bank Holding Corporation, 800 North Shoreline Boulevard, Corpus Christi, Texas 78401, Attn: Stephen Raffaele, (512) 306-5550 or, with respect to the Prosperity/Southwest Proxy Statement/Prospectus, Southwest Bancshares, Inc., 1900 NW Loop 410, San Antonio, Texas 78213, Attention: Investor Relations, (210) 807-5511, as applicable.

No Offer or Solicitation

This communication is for informational purposes only and is not intended to and does not constitute an offer to subscribe for, buy or sell, or the solicitation of an offer to subscribe for, buy or sell, or an invitation to subscribe for, buy or sell any securities or a solicitation of any vote or approval in any jurisdiction, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in which such offer, invitation, sale or solicitation would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act, and otherwise in accordance with applicable law.

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Prosperity Bancshares, Inc.®

Financial Highlights (Unaudited)

(In thousands)

(A) Includes $(1,987), $(1,657), $(1,374), $(2,056) and $(1,070) in unrealized losses on available for sale securities for the quarterly periods ended September 30, 2025, June 30, 2025, March 31, 2025, December 31, 2024 and September 30, 2024 respectively.

(B) Includes $(1,570), $(1,309), $(1,085), $(1,624) and $(845) in after-tax unrealized losses on available for sale securities for the quarterly periods ended September 30, 2025, June 30, 2025, March 31, 2025, December 31, 2024 and September 30, 2024, respectively.

Prosperity Bancshares, Inc.®

Financial Highlights (Unaudited)

(In thousands)