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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of
the Securities Exchange Act of 1934 (Amendment No.          )

MERGER PROPOSAL—YOUR VOTE IS VERY IMPORTANT

          Dear stockholders of Twilio Inc. and stockholders of SendGrid, Inc.:

          As previously announced, the board of directors of Twilio Inc., which we refer to as Twilio, and the board of directors of SendGrid, Inc., which we refer to as SendGrid, have approved an acquisition of SendGrid by Twilio. Twilio, SendGrid, and Topaz Merger Subsidiary, Inc., which we refer to as Merger Sub, entered into an Agreement and Plan of Merger and Reorganization, dated as of October 15, 2018, as amended on December 13, 2018 and as may be further amended from time to time, pursuant to which Merger Sub will merge with and into SendGrid, with SendGrid continuing as a direct wholly owned subsidiary of Twilio.

          If the transaction is completed, SendGrid stockholders will have the right to receive 0.485 of a share, which we refer to as the exchange ratio, of Twilio Class A common stock for each share of SendGrid common stock they own at the closing, with cash paid in lieu of fractional shares. The exchange ratio is fixed and will not be adjusted to reflect stock price changes prior to the closing of the merger. Based on the closing price of Twilio Class A common stock on the New York Stock Exchange, or NYSE, of $76.13 on October 15, 2018, the last trading day before public announcement of the merger, the merger consideration represented approximately $36.92 of aggregate value for each share of SendGrid common stock. Based on the Twilio closing price of $95.97 on December 13, 2018, the latest practicable date before the date of this document, the merger consideration represented approximately $46.55 of aggregate value for each share of SendGrid common stock. Twilio stockholders will continue to own their existing shares of Twilio Class A common stock. We encourage you to obtain current market quotations of Twilio Class A common stock and SendGrid common stock before voting.

          Twilio estimates that it may issue up to approximately 23,114,713 million shares of its Class A common stock to SendGrid stockholders in the merger pursuant to the merger agreement. Upon completion of the merger, we estimate that current Twilio stockholders will own approximately 81.2% of the combined company and former SendGrid stockholders will own approximately 18.8% of the combined company. Twilio Class A common stock and SendGrid common stock are both traded on the NYSE under the symbols "TWLO" and "SEND", respectively. Upon completion of the merger, SendGrid common stock will cease to be traded on the NYSE.

          At the special meeting of Twilio stockholders to be held on January 30, 2019, Twilio stockholders will be asked to vote on (i) a proposal to approve the issuance of shares of Twilio Class A common stock to SendGrid stockholders, which is a condition to completion of the merger, which we refer to as the Twilio stock issuance proposal, and (ii) a proposal to approve adjournments of the Twilio special meeting, if necessary and appropriate, to solicit additional proxies if there are not sufficient votes to approve the issuance of shares of Twilio Class A common stock in the merger, which we refer to as the Twilio adjournment proposal. At the special meeting of SendGrid stockholders to be held on January 30, 2019, SendGrid stockholders will be asked to vote on (i) a proposal to adopt the merger agreement, which we refer to as the SendGrid merger proposal, (ii) a proposal to approve, on an advisory (non-binding) basis, the compensation that may be paid or become payable to SendGrid's named executive officers that is based on or otherwise relates to the merger agreement and the transactions contemplated by the merger agreement, which we refer to as the SendGrid compensation proposal, and (iii) a proposal to approve adjournments of the SendGrid special meeting, if necessary and appropriate, to solicit additional proxies if there are not sufficient votes to adopt the merger agreement, which we refer to as the SendGrid adjournment proposal.

          We cannot complete the merger unless the SendGrid stockholders and the Twilio stockholders approve the respective proposals related to the merger. Your vote is very important, regardless of the number of shares you own. Whether or not you expect to attend the Twilio special meeting or SendGrid special meeting, as applicable, in person, please vote your shares as promptly as possible by (1) accessing the Internet website specified on your proxy card, (2) calling the toll-free number specified on your proxy card, or (3) signing and returning all proxy cards that you receive in the postage-paid envelope provided, so that your shares may be represented and voted at the Twilio or the SendGrid special meeting, as applicable. If you are a SendGrid stockholder, please note that a failure to vote your shares is the equivalent of a vote against the merger. If you are a Twilio stockholder, please note that a failure to vote your shares may result in a failure to establish a quorum for the Twilio special meeting.

          The Twilio board of directors, which we refer to as the Twilio Board, recommends that Twilio stockholders vote "FOR" the Twilio stock issuance proposal and, if necessary, "FOR" the Twilio adjournment proposal. The SendGrid board of directors, which we refer to as the SendGrid Board, recommends that SendGrid stockholders vote "FOR" the SendGrid merger proposal, "FOR" the SendGrid compensation proposal and, if necessary, "FOR" the SendGrid adjournment proposal.

          The obligations of Twilio and SendGrid to complete the merger are subject to the satisfaction or waiver of several conditions set forth in the merger agreement. More information about Twilio, SendGrid and the merger is contained in this joint proxy statement/prospectus. Twilio and SendGrid encourage you to read this entire joint proxy statement/prospectus carefully, including the section entitled "Risk Factors" beginning on page 36.

          We look forward to the successful merger of Twilio and SendGrid.

Sincerely,		Sincerely,
Jeff Lawson Chief Executive Officer, Director and Chairman Twilio Inc.		Sameer Dholakia President, Chief Executive Officer, Director and Chairman SendGrid, Inc.

          Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be issued under this joint proxy statement/prospectus or determined that this joint proxy statement/prospectus is accurate or complete. Any representation to the contrary is a criminal offense.

          This joint proxy statement/prospectus is dated December 18, 2018 and is first being mailed to the stockholders of Twilio and stockholders of SendGrid on or about December 18, 2018.

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Twilio Inc.
375 Beale Street, Suite 300
San Francisco, California 94105
(415) 390-2337

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS TO BE HELD ON JANUARY 30, 2019

Dear Twilio stockholders:

        We are pleased to invite you to attend the special meeting of the Twilio stockholders, which will be held at the offices of Goodwin Procter LLP, located at Three Embarcadero Center, 28th Floor, San Francisco, California 94111, on January 30, 2019, at 8:00 a.m., local time, which we refer to as the Twilio special meeting, for the following purposes:

•

To vote on a proposal to approve the issuance of Twilio Class A common stock to SendGrid stockholders in connection with the merger contemplated by the Agreement and Plan of Merger and Reorganization, dated October 15, 2018, as amended on December 13, 2018 and as may be further amended from time to time, among Twilio Inc., Topaz Merger Subsidiary, Inc. and SendGrid, Inc., which we refer to as the merger agreement and which is attached as Annex A to the joint proxy statement/prospectus accompanying this notice. We refer to this proposal as the Twilio stock issuance proposal.



•

To vote on a proposal to approve adjournments of the Twilio special meeting, if necessary and appropriate, to solicit additional proxies if there are not sufficient votes to approve the Twilio stock issuance proposal. We refer to this proposal as the Twilio adjournment proposal.

        Twilio will transact no other business at the special meeting except such business as may properly be brought before the special meeting or any adjournment or postponement thereof. Please refer to the attached joint proxy statement/prospectus for further information with respect to the business to be transacted at the Twilio special meeting.

        At a meeting of the Twilio Board held on October 15, 2018, the Twilio Board determined that the merger agreement and the transactions contemplated thereby, including the issuance of Twilio Class A common stock to the SendGrid stockholders in connection with the merger, are in the best interests of Twilio and its stockholders, and approved the merger agreement and the merger, the execution of the merger agreement and the consummation of the transactions contemplated thereby.

        The Twilio Board recommends that Twilio stockholders vote "FOR" the Twilio stock issuance proposal and "FOR" the Twilio adjournment proposal.

        Holders of record of shares of Twilio Class A common stock and Twilio Class B common stock, at the close of business on December 13, 2018, which we refer to as the Twilio record date, are entitled to notice of, and may vote at, the Twilio special meeting and any adjournment of the special meeting. A list of Twilio stockholders entitled to vote at the Twilio special meeting will be available for inspection at Twilio's principal executive offices, located at 375 Beale Street, Suite 300, San Francisco, California 94105, at least 10 days prior to the date of the Twilio special meeting and continuing through the date thereof for any purpose germane to the Twilio special meeting, between the hours of 9:00 a.m. and 4:30 p.m., local time. The list will also be available at the Twilio special meeting for inspection by any Twilio stockholder present at the Twilio special meeting.

        Approval of the Twilio stock issuance proposal requires the affirmative vote of a majority in combined voting power of the holders of Twilio Class A common stock and Twilio Class B common stock, voting together as a single class, present in person or by proxy entitled to vote on such matter at the Twilio special meeting (provided that a quorum exists). Approval of the Twilio adjournment proposal requires the affirmative vote of a majority of votes cast at the Twilio special meeting by the

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holders of Twilio Class A common stock and Twilio Class B common stock, voting together as a single class, present in person or by proxy at the Twilio special meeting (whether or not a quorum is present).

        Your vote is important. Whether or not you expect to attend the Twilio special meeting in person, we urge you to vote your shares as promptly as possible by (1) accessing the Internet website specified on your proxy card; (2) calling the toll-free number specified on your proxy card; or (3) signing and returning the enclosed proxy card in the postage-paid envelope provided, so that your shares may be represented and voted at the Twilio special meeting. If your shares are held in the name of a bank, broker or other fiduciary, please follow the instructions on the voting instruction card furnished by the record holder.

        If you have any questions or need assistance voting your shares, please call Twilio's proxy solicitor, Innisfree M&A Incorporated, toll-free at (888) 750-5834.

		By Order of the Board of Directors,
		Jeff Lawson Chief Executive Officer
		San Francisco, California
		December 18, 2018

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SendGrid, Inc.
1801 California Street, Suite 500
Denver, Colorado 80202
(888) 985-7363

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS TO BE HELD ON JANUARY 30, 2019

Dear SendGrid stockholders:

        We are pleased to invite you to attend the special meeting of the SendGrid stockholders, which will be held at the offices of SendGrid located at 1801 California Street, Suite 500, Denver, Colorado 80202, on January 30, 2019, at 9:00 a.m., local time, which we refer to as the SendGrid special meeting, for the following purposes:

•

To vote on a proposal to adopt the Agreement and Plan of Merger and Reorganization, dated October 15, 2018, among Twilio Inc., Topaz Merger Subsidiary, Inc., and SendGrid, Inc., as amended on December 13, 2018 and as such agreement may be further amended from time to time. A copy of the merger agreement is attached as Annex A to the joint proxy statement/prospectus accompanying this notice;



•

To vote on a proposal to approve, on an advisory (non-binding) basis, the compensation that may be paid or become payable to SendGrid's named executive officers that is based on or otherwise relates to the merger agreement and the transactions contemplated by the merger agreement; and



•

To vote on a proposal to approve adjournments of the SendGrid special meeting, if necessary and appropriate, to solicit additional proxies if there are not sufficient votes to approve the SendGrid merger proposal.

        SendGrid will transact no other business at the special meeting except such business as may properly be brought before the special meeting or any adjournment or postponement thereof. Please refer to the attached joint proxy statement/prospectus for further information with respect to the business to be transacted at the SendGrid special meeting.

        At a meeting of the SendGrid Board held on October 15, 2018, the SendGrid Board determined that the merger agreement and the transactions contemplated thereby, including the merger, are advisable and in the best interests of SendGrid and its stockholders, and approved the merger agreement and the merger, the execution of the merger agreement and the consummation of the transactions contemplated thereby and declared advisable and recommended that SendGrid's stockholders adopt the merger agreement.

        The SendGrid Board recommends that SendGrid stockholders vote "FOR" the SendGrid merger proposal, "FOR" the SendGrid compensation proposal and "FOR" the SendGrid adjournment proposal.

        Holders of record of shares of SendGrid common stock, at the close of business on December 13, 2018, which we refer to as the SendGrid record date, are entitled to notice of, and may vote at, the special meeting and any adjournment of the special meeting. A list of SendGrid stockholders entitled to vote at the SendGrid special meeting will be available for inspection at SendGrid's principal executive offices, located at 1801 California Street, Suite 500, Denver, Colorado 80202, at least 10 days prior to the date of the SendGrid special meeting and continuing through the date thereof for any purpose germane to the SendGrid special meeting, between the hours of 9:00 a.m. and 4:30 p.m., local time. The list will also be available at the SendGrid special meeting for inspection by any SendGrid stockholder present at the SendGrid special meeting.

        Approval of the SendGrid merger proposal requires the affirmative vote of a majority of the outstanding shares of SendGrid's common stock. Approval, on an advisory (non-binding) basis, of the

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SendGrid compensation proposal requires the affirmative vote of a majority of the shares of SendGrid common stock present at the meeting in person or by proxy. Approval of the SendGrid adjournment proposal requires the affirmative vote of a majority of the shares of SendGrid common stock present at the meeting in person or by proxy.

        Your vote is important. Whether or not you expect to attend the SendGrid special meeting in person, we urge you to vote your shares as promptly as possible by (1) accessing the Internet website specified on your proxy card; (2) calling the toll-free number specified on your proxy card; or (3) signing and returning the enclosed proxy card in the postage-paid envelope provided, so that your shares may be represented and voted at the SendGrid special meeting. If your shares are held in the name of a bank, broker or other fiduciary, please follow the instructions on the voting instruction card furnished by the record holder.

        If you have any questions or need assistance voting your shares, please call SendGrid's proxy solicitor, MacKenzie Partners, Inc., toll-free at (800) 322-2885.

		By Order of the Board of Directors,
		Sameer Dholakia President, Chief Executive Officer, Director and Chairman
		Denver, Colorado
		December 18, 2018

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ADDITIONAL INFORMATION

        This joint proxy statement/prospectus incorporates important business and financial information about Twilio and SendGrid from other documents that are not included in or delivered with this joint proxy statement/prospectus. For a listing of documents incorporated by reference into this joint proxy statement/prospectus, please see the section entitled "Where You Can Find More Information" beginning on page 199 of this joint proxy statement/prospectus. This information is available to you without charge upon your request.

        You can obtain the documents incorporated by reference into this joint proxy statement/prospectus by requesting them in writing or by telephone from the appropriate company at the following addresses and telephone numbers:

        Investors may also consult Twilio's or SendGrid's website for more information concerning the merger described in this joint proxy statement/prospectus. Twilio's website is www.twilio.com. SendGrid's website is www.sendgrid.com. Information included on these websites is not incorporated by reference into this joint proxy statement/prospectus.

        In addition, if you have questions about the merger or the accompanying joint proxy statement/prospectus, would like additional copies of the joint proxy statement/prospectus, or need to obtain proxy cards or other information related to the proxy solicitation, please call Innisfree M&A Incorporated, the proxy solicitor for Twilio, toll-free at (888) 750-5834, or MacKenzie Partners, Inc., the proxy solicitor for SendGrid, toll-free at (800) 322-2885. You will not be charged for any of these documents that you request.

        If you would like to request any documents, please do so no later than five business days before the date of the relevant special meeting in order to receive timely delivery of such documents before such special meeting. Therefore, if you would like to request documents from Twilio, please do so by January 23, 2019 and if you would like to request documents from SendGrid, please do so by January 23, 2019 in order to receive such documents before the Twilio and SendGrid special meetings, respectively.

ABOUT THIS DOCUMENT

        This joint proxy statement/prospectus, which forms part of a registration statement on Form S-4 filed with the Securities and Exchange Commission, which we refer to as the SEC, by Twilio (File No. 333-228522), constitutes a prospectus of Twilio under Section 5 of the Securities Act of 1933, as amended, which we refer to as the Securities Act, with respect to the shares of Twilio Class A common stock proposed to be issued to SendGrid stockholders pursuant to the merger agreement. This document also constitutes a joint proxy statement under Section 14(a) of the Securities Exchange Act of 1934, as amended, which we refer to as the Exchange Act. It also includes a notice of meeting with respect to the special meeting of Twilio stockholders, at which Twilio stockholders will be asked to vote upon the Twilio stock issuance proposal, and a notice of meeting with respect to the special meeting of SendGrid stockholders, at which SendGrid stockholders will be asked to vote upon a proposal to adopt the merger agreement.

        Twilio has supplied all information contained in this joint proxy statement/prospectus-information statement relating to Twilio and Merger Sub. SendGrid has supplied all information contained in or incorporated by reference into this joint proxy statement/prospectus-information statement relating to SendGrid. Twilio and SendGrid have both contributed information relating to the proposed transactions.

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        Before casting your vote, you should carefully review all the information contained or incorporated by reference into this joint proxy statement/prospectus. Neither Twilio nor SendGrid has authorized anyone to provide you with information that is different from that contained in, or incorporated by reference into, this joint proxy statement/prospectus. This joint proxy statement/prospectus is dated December 18, 2018. You should not assume that the information contained in, or incorporated by reference into, this joint proxy statement/prospectus is accurate as of any date other than the date on the front cover of those documents. Neither the mailing of this joint proxy statement/prospectus to Twilio stockholders or SendGrid stockholders nor the issuance by Twilio of common stock in connection with the merger will create any implication to the contrary.

        In deciding how to vote with respect to any of the proposals discussed herein, you must make your own independent examination of the merits and risks of the proposal. You should not construe anything included in this joint proxy statement/prospectus as investment, legal, business or tax advice, and should consult with your own advisors if you have questions concerning any of the matters described herein.

        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. As permitted by SEC rules, this joint proxy statement/prospectus does not contain all of the information you can find in Twilio's registration statement or its exhibits. For further information pertaining to Twilio and the shares of Twilio Class A common stock to be issued in connection with the merger, reference is made to that registration statement and its exhibits. Statements contained in this document or in any document incorporated into this document by reference as to the contents of any contract or other document referred to in this document or in other documents that are incorporated by reference into this document are not necessarily complete and, in each instance, reference is made to the copy of the applicable contract or other document filed as an exhibit to the registration statement or otherwise filed with the SEC. Each statement contained in this document is qualified in its entirety by reference to the underlying documents. You are encouraged to read the entire registration statement. You may obtain copies of the Form S-4 including documents incorporated by reference into the Form S-4 (and any amendments to those documents) by following the instructions under "Where You Can Find More Information."

        All references in this joint proxy statement/prospectus to "SendGrid" refer to SendGrid, Inc., a Delaware corporation (except that in connection with the description of its operations or business under the headings "Cautionary Statement Regarding Forward-Looking Statements" and "Risk Factors," such term refers to the consolidated operations of SendGrid and its subsidiaries); all references in this joint proxy statement/prospectus to "Twilio" refer to Twilio Inc., a Delaware corporation (except that in connection with the description of its operations or business under the headings "Cautionary Statement Regarding Forward-Looking Statements" and "Risk Factors," such term refers to the consolidated operations of Twilio and its subsidiaries); and all references to "Merger Sub" refer to Topaz Merger Subsidiary, Inc., a Delaware corporation and a direct wholly owned subsidiary of Twilio, formed for the purpose of effecting the merger. Unless otherwise indicated or as the context requires, all references to the "merger agreement" refer to the Agreement and Plan of Merger and Reorganization, dated as of October 15, 2018, among Twilio, SendGrid and Merger Sub, as amended on December 13, 2018 and as may be further amended from time to time, a copy of which is included as Annex A to this joint proxy statement/prospectus.

TRADEMARKS AND SERVICE MARKS

        Twilio and SendGrid own or have rights to various trademarks, logos, service marks and trade names that each uses in connection with the operation of its business. Twilio and SendGrid each also own or have the rights to copyrights that protect the content of their respective products. Solely for convenience, the trademarks, service marks, trade names and copyrights referred to in this joint proxy statement/prospectus-information statement are listed without the ™, ® and © symbols, but such references do not constitute a waiver of any rights that might be associated with the respective trademarks, service marks, trade names and copyrights included or referred to in this joint proxy statement/prospectus-information statement.

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QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE SPECIAL MEETING

        The following are brief answers to certain questions that Twilio stockholders and SendGrid stockholders may have regarding the merger, the merger agreement, the issuance of shares of Twilio Class A common stock in connection with the merger, the Twilio special meeting, the SendGrid special meeting, and other matters to be considered at the Twilio special meeting and at the SendGrid special meeting. Twilio and SendGrid urge you to read carefully the remainder of this joint proxy statement/prospectus and additional important information contained in the annexes and exhibits to, and the documents incorporated by reference into, this joint proxy statement/prospectus because the information in this section may not provide all of the information that might be important to you in determining how to vote. See "Where You Can Find More Information" beginning on page 199 in this joint proxy statement/prospectus.

Q:

What is the proposed transaction?

A:

On October 15, 2018, Twilio, SendGrid, and Topaz Merger Subsidiary, Inc., a direct, wholly owned subsidiary of Twilio, which we refer to as Merger Sub, entered into an Agreement and Plan of Merger and Reorganization, which we refer to as the merger agreement. A copy of the merger agreement as amended on December 13, 2018, is attached to this joint proxy statement/prospectus as Annex A.

Under the terms of the merger agreement, Merger Sub will merge with and into SendGrid, with SendGrid continuing as a wholly owned subsidiary of Twilio, which we refer to as the merger. If the merger is completed, holders of SendGrid common stock, which we refer to as SendGrid stockholders, will have the right to receive 0.485, which we refer to as the exchange ratio, of a share of Twilio Class A common stock for each share of SendGrid common stock they own at closing of the merger, with cash to be paid in lieu of fractional shares. The exchange ratio is fixed and will not be adjusted to reflect stock price changes prior to the closing of the merger. Holders of Twilio common stock, which we refer to as Twilio stockholders, will not receive any merger consideration and will continue to hold their shares of Twilio Class A common stock and/or Twilio Class B common stock.

Q:

Why am I receiving this joint proxy statement/prospectus?

A:

In order to complete the merger, among other things:

•

Twilio stockholders must vote to approve the issuance of shares of Twilio Class A common stock to SendGrid stockholders in connection with the merger, which we refer to as the Twilio stock issuance proposal; and

•

SendGrid stockholders must vote to adopt the merger agreement, which we refer to as the SendGrid merger proposal.

Twilio is holding a special meeting of stockholders, in order to obtain the stockholder approval necessary to approve the Twilio stock issuance proposal. Twilio stockholders will also be asked to approve adjournments of the Twilio special meeting if necessary and appropriate to solicit additional proxies if there are not sufficient votes at the time of the Twilio special meeting, or any adjournment or postponement thereof, to approve the stock issuance, which we refer to as the Twilio adjournment proposal. It is important that Twilio stockholders vote their Twilio Class A common stock and Twilio Class B common stock on each of these matters, regardless of the number of shares owned.

SendGrid is holding a special meeting of stockholders to obtain their approval to adopt the merger agreement. In addition, SendGrid stockholders will also be asked to approve adjournments of the SendGrid special meeting if necessary and appropriate to solicit additional proxies if there are not sufficient votes to adopt the merger agreement at the time of the SendGrid special meeting or any

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adjournment or postponement thereof, which we refer to as the SendGrid adjournment proposal, and to approve, on an advisory (non-binding) basis, the compensation that may be paid or become payable to SendGrid's named executive officers, who are referred to as the named executive officers, in connection with the merger, which we refer to as the SendGrid compensation proposal. It is important that SendGrid stockholders vote their SendGrid common stock on each of these matters, regardless of the number of shares owned.

Your vote is important. We encourage you to vote as soon as possible.

Q:

Who is soliciting my proxy?

A:

Proxies in the form enclosed with this joint proxy statement/prospectus are being solicited from the Twilio stockholders by the Twilio board. Proxies in the form enclosed with this joint proxy statement/prospectus are being solicited from the SendGrid stockholders by the SendGrid Board.

Q:

When and where will the meetings be held?

A:

The Twilio special meeting will be held at the offices of Goodwin Procter LLP, located at Three Embarcadero Center, 28th Floor, San Francisco, California 94111, on January 30, 2019, at 8:00 a.m., local time.

The SendGrid special meeting will be held at the offices of SendGrid, located at 1801 California Street, Suite 500, Denver, Colorado 80202, on January 30, 2019, at 9:00 a.m., local time.

Q:

What will SendGrid stockholders receive in the merger?

A:

Because Twilio has agreed to issue 0.485 of a share of Twilio Class A common stock in exchange for each share of SendGrid common stock, the value of the merger consideration that SendGrid stockholders will receive will depend on the price per share of Twilio Class A common stock at the effective time of the merger. That price may be more or less than the current price or the price on the last trading day before public announcement of the merger. The exchange ratio will not be adjusted for changes in the market price of either Twilio Class A common stock or SendGrid common stock between the date of signing the merger agreement and completion of the merger.

Based on the closing price of Twilio Class A common stock on the NYSE of $76.13 on October 15, 2018, the last trading day before public announcement of the merger, the merger consideration represented approximately $36.92 of aggregate value for each share of SendGrid common stock. Based on the Twilio closing price of $95.97 on December 13, 2018, the latest practicable date before the date of this joint proxy statement/prospectus, the merger consideration represented approximately $46.55 of aggregate value for each share of SendGrid common stock.

Twilio stockholders will continue to own their existing shares of Twilio Class A common stock and/or Twilio Class B common stock. Twilio Class A common stock is currently traded on the NYSE under the symbol "TWLO," and SendGrid common stock is currently traded on the NYSE under the symbol "SEND."

We encourage you to obtain current market quotations of Twilio Class A common stock and SendGrid common stock before voting.

Q:

How does the stock exchange ratio affect the ownership of Twilio after completion of the merger?

A:

Because the stock exchange ratio is fixed, to the extent that the number of shares of outstanding Twilio Class A common stock or SendGrid common stock changes prior to completion of the merger, whether due to any new issuance of shares of Twilio Class A common stock or SendGrid common stock, any exercise of any outstanding options or other rights to purchase shares of Twilio

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Class A common stock or SendGrid common stock or otherwise, there will automatically occur a corresponding change in the relative ownership percentages of the current Twilio stockholders and the current SendGrid stockholders of the combined company.

In the event of any reclassification, stock split, reverse stock split, stock dividend, stock distribution, recapitalization, subdivision or other similar transaction with respect to the shares of SendGrid common stock or shares of Twilio Class A common stock prior to the effective time of the merger, the merger consideration will be equitably adjusted to eliminate the effects of such event on the merger consideration as contemplated by the merger agreement.

Q:

How do I vote?

A:

If you are a stockholder of record of Twilio as of the record date for the Twilio special meeting or a stockholder of record of SendGrid as of the record date for the SendGrid special meeting, you may vote in person by attending the Twilio special meeting or, to ensure your shares are represented at the meeting, you may vote by:

•

accessing the Internet website specified on your proxy card;

•

calling the toll-free number specified on your proxy card; or

•

signing and returning the enclosed proxy card in the postage-paid envelope provided.

If you hold shares of Twilio Class A common stock and/or Twilio Class B common stock or shares of SendGrid common stock in the name of a broker or nominee, please follow the voting instructions provided by your broker or nominee to ensure that your shares are represented at the Twilio special meeting.

Q:

What are the voting deadlines?

A:

If you are a Twilio stockholder, the deadline for submitting a proxy using the Internet or the telephone is 11:59 p.m. Eastern time on January 29, 2019. If you received your special meeting materials by mail, you may complete, sign and date the proxy card or voting instruction card and return it in the prepaid envelope. All holders of Twilio Class A common stock and Twilio Class B common stock as of the close of business on the record date for the Twilio special meeting may vote in person at the Twilio special meeting. For detailed information, see the section entitled "The Twilio Special Meeting."

If you are a SendGrid stockholder, the deadline for submitting a proxy using the Internet or the telephone is 11:59 p.m. Eastern time on January 29, 2019. If you received your special meeting materials by mail, you may complete, sign and date the proxy card or voting instruction card and return it in the prepaid envelope. All holders of SendGrid common stock as of the close of business on the record date may vote in person at the SendGrid special meeting. For detailed information, see the section entitled "The SendGrid Special Meeting."

Q:

What vote is required to approve each proposal at the Twilio special meeting?

A:

Twilio Stock Issuance Proposal.    Approval of the Twilio stock issuance proposal requires the affirmative vote of a majority in combined voting power of the holders of Twilio Class A common stock and Twilio Class B common stock, voting together as a single class, present in person or by proxy entitled to vote on such matter at the Twilio special meeting (provided that a quorum exists). For the Twilio stock issuance proposal, an abstention will have the effect of a vote against the proposal. Broker "non-votes" will have no effect on the outcome of the proposal. Shares of Twilio Class A common stock and Twilio Class B common stock represented by properly executed, timely received and unrevoked proxies will be voted in accordance with the instructions indicated thereon.

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If you are a Twilio stockholder of record and you sign and return your proxy card without indicating how to vote on any particular proposal, the shares of Twilio Class A common stock and Twilio Class B common stock represented by your proxy will be counted as present for purposes of determining the presence of a quorum for the Twilio special meeting and will be voted "FOR" that proposal.

Twilio Adjournment Proposal.    Approval of the Twilio adjournment proposal requires the affirmative vote of a majority of the votes cast at the Twilio special meeting by holders of shares of Twilio Class A common stock and Twilio Class B common stock, voting together as a single class (whether or not a quorum is present). For the Twilio adjournment proposal, an abstention will have the effect of a vote against the proposal. Broker "non-votes" will have no effect on the outcome of the proposal. Shares of Twilio Class A common stock and Twilio Class B common stock represented by properly executed, timely received and unrevoked proxies will be voted in accordance with the instructions indicated thereon. If you are a Twilio stockholder of record and you sign and return your proxy card without indicating how to vote on any particular proposal, the shares of Twilio Class A common stock and Twilio Class B common stock represented by your proxy will be counted as present for purposes of determining the presence of a quorum for the Twilio special meeting and will be voted "FOR" that proposal.

Q:

What vote is required to approve each proposal at the SendGrid special meeting?

A:

SendGrid Merger Proposal.    Approval of the SendGrid merger proposal requires the affirmative vote of a majority of the outstanding shares of SendGrid's common stock. Failure to vote in person or by proxy at the special meeting, abstentions, and broker non-votes (if any) will have the same effect as a vote against the SendGrid merger proposal. Shares of SendGrid common stock represented by properly executed, timely received and unrevoked proxies will be voted in accordance with the instructions indicated thereon. If you are a SendGrid stockholder of record and you sign and return your proxy card without indicating how to vote on any particular proposal, the shares of SendGrid common stock represented by your proxy will be counted as present for purposes of determining the presence of a quorum for the SendGrid special meeting and will be voted "FOR" that proposal.

SendGrid Compensation Proposal.    Approval, on an advisory (non-binding) basis, of the SendGrid compensation proposal requires the affirmative vote of a majority of the shares of SendGrid common stock present at the meeting in person or by proxy. Assuming a quorum is present, (i) a failure to vote in person or by proxy at the SendGrid special meeting will have no effect on the outcome of the SendGrid compensation proposal, (ii) abstentions will be treated as votes cast and, therefore, will have the same effect as a vote against the SendGrid compensation proposal and (iii) broker "non-votes" (if any) will have no effect on the outcome of the SendGrid compensation proposal. Shares of SendGrid common stock represented by properly executed, timely received and unrevoked proxies will be voted in accordance with the instructions indicated thereon. If you are a SendGrid stockholder of record and you sign and return your proxy card without indicating how to vote on any particular proposal, the shares of SendGrid common stock represented by your proxy will be counted as present for purposes of determining the presence of a quorum for the SendGrid special meeting and will be voted "FOR" that proposal.

SendGrid Adjournment Proposal.    Approval of the SendGrid adjournment proposal requires the affirmative vote of a majority of the shares of SendGrid common stock present at the meeting in person or by proxy. Assuming a quorum is present, (i) a failure to vote in person or by proxy at the SendGrid special meeting will have no effect on the outcome of the SendGrid adjournment proposal, (ii) abstentions will be treated as votes cast and, therefore, will have the same effect as a vote against the SendGrid adjournment proposal and (iii) broker "non-votes" (if any) will have no effect on the outcome of the SendGrid adjournment proposal. Shares of SendGrid common stock

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represented by properly executed, timely received and unrevoked proxies will be voted in accordance with the instructions indicated thereon. If you are a SendGrid stockholder of record and you sign and return your proxy card without indicating how to vote on any particular proposal, the shares of SendGrid common stock represented by your proxy will be counted as present for purposes of determining the presence of a quorum for the SendGrid special meeting and will be voted "FOR" that proposal.

Q:

Are there any voting agreements with existing stockholders?

A:

Yes. On October 15, 2018, concurrently with the execution and delivery of the merger agreement, certain stockholders and certain directors and executive officers of SendGrid, in their respective capacities as stockholders of SendGrid, but not including Byron Deeter or Bessemer Venture Partners and its affiliates, entered into voting agreements with Twilio, pursuant to which such stockholders and individuals have agreed, among other things, to vote their respective shares of SendGrid common stock for the adoption of the merger agreement and the approval of the merger and the other transactions contemplated by the merger agreement. As of the public announcement of the merger, the stockholders who signed the SendGrid voting agreements owned an aggregate of approximately 6.4% of the outstanding shares of SendGrid common stock. As of the record date for the SendGrid special meeting, the stockholders who signed the SendGrid voting agreements owned an aggregate of approximately 6.7% of the outstanding shares of SendGrid common stock. The forms of SendGrid voting agreement are attached to this joint proxy statement/prospectus as Annexes D and E.

Similarly, on October 15, 2018, concurrently with the execution and delivery of the merger agreement, certain directors and executive officers of Twilio, in their respective capacities as stockholders of Twilio, but not including Byron Deeter or Bessemer Venture Partners and its affiliates, entered into voting agreements with SendGrid, pursuant to which such stockholders have agreed, among other things, to vote their respective shares of Twilio Class A common stock in favor of the approval of the issuance of shares of Twilio Class A common stock pursuant to the merger agreement. In connection with the execution and delivery of the merger agreement, certain persons, including such directors and officers, who hold Twilio Class B common stock granted an irrevocable proxy to an independent director of Twilio, pursuant to which such shares of Twilio Class B common stock will, among other things, be voted in favor of the approval of the issuance of shares of Twilio Class A common stock pursuant to the merger agreement. As of the public announcement of the merger, the stockholders who signed the Twilio voting agreements and/or granted the irrevocable proxy owned an aggregate of approximately 33.2% of the voting power of the outstanding Twilio Class A common stock and Twilio Class B common stock calculated in the aggregate. As of the record date for the Twilio special meeting, the stockholders who signed the Twilio voting agreements and/or granted the irrevocable proxy owned an aggregate of approximately 33.1% of the voting power of the outstanding Twilio Class A common stock and Twilio Class B common stock calculated in the aggregate. The forms of Twilio voting agreement are attached to this joint proxy statement/prospectus as Annexes F and G.

Q:

How does the SendGrid Board recommend that SendGrid stockholders vote?

A:

At a meeting of the SendGrid Board held on October 15, 2018, the SendGrid Board determined that the merger agreement and the transactions contemplated thereby, including the merger, are advisable and in the best interests of SendGrid and its stockholders, and approved the merger agreement and the merger, the execution of the merger agreement and the consummation of the transactions contemplated thereby and declared advisable and recommended that SendGrid's stockholders adopt the merger agreement. Such determination, approval and recommendation were made unanimously by the SendGrid Board with the exception of director Byron Deeter, who

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recused himself from all deliberations due to his concurrent service as a director of Twilio. The SendGrid Board recommends that SendGrid stockholders vote "FOR" the SendGrid merger proposal, "FOR" the SendGrid compensation proposal and "FOR" the SendGrid adjournment proposal.

Q:

How does the Twilio Board recommend that Twilio stockholders vote?

A:

At a meeting of the Twilio Board held on October 15, 2018, the Twilio Board determined that the merger agreement and the transactions contemplated thereby, including the issuance of Twilio Class A common stock to the SendGrid stockholders in connection with the merger, are in the best interests of Twilio and its stockholders, and approved the merger agreement and the merger, the execution of the merger agreement and the consummation of the transactions contemplated thereby. Such determination, approval and recommendation were made unanimously by the Twilio Board with the exception of director Byron Deeter, who recused himself from all deliberations due to his concurrent service as a director of SendGrid and his position as a partner of Bessemer, and Jeffrey Epstein who recused himself from all deliberations due to his position as an operating partner of Bessemer and stockholder of SendGrid. The Twilio Board recommends that Twilio stockholders vote "FOR" the Twilio stock issuance proposal and "FOR" the Twilio adjournment proposal.

Q:

How many votes do I have?

A:

Twilio.    You are entitled to one vote for each share of Twilio Class A common stock that you owned as of the Twilio record date and 10 votes for each share of Twilio Class B common stock that you owned as of the Twilio record date. As of the close of business on December 13, 2018, there were 80,667,248 outstanding shares of Twilio Class A common stock and 19,349,115 outstanding shares of Twilio Class B common stock. As of that date, 0.6% of the outstanding shares of Twilio Class A common stock and 68.8% of the outstanding shares of Twilio Class B common stock were beneficially owned by the directors and executive officers of Twilio, representing 48.8% of the total Twilio voting power.

SendGrid.    You are entitled to one vote for each share of SendGrid common stock that you owned as of the SendGrid record date. As of the close of business on December 13, 2018, there were 47,659,204 outstanding shares of SendGrid common stock. As of that date, 20% of the outstanding shares of SendGrid common stock were beneficially owned by the directors and executive officers of SendGrid.

Q:

What will happen if I fail to vote or I abstain from voting?

A:

Twilio.    If you are a Twilio stockholder, abstentions have the effect of a vote against the Twilio stock issuance proposal and, if necessary, the Twilio adjournment proposal. Broker "non-votes" have no effect on the outcome of the Twilio stock issuance proposal or the Twilio adjournment proposal. Shares of Twilio Class A common stock and Twilio Class B common stock represented by properly executed, timely received and unrevoked proxies will be voted in accordance with the instructions indicated thereon. If you are a Twilio stockholder of record and you sign and return your proxy card without indicating how to vote on any particular proposal, the shares of Twilio Class A common stock and Twilio Class B common stock represented by your proxy will be counted as present for purposes of determining the presence of a quorum for the Twilio special meeting and will be voted "FOR" that proposal.

SendGrid.    If you are a SendGrid stockholder, failure to vote in person or by proxy at the SendGrid special meeting, abstentions, and broker non-votes (if any) will have the same effect as a vote against the SendGrid merger proposal. Assuming a quorum is present, (i) a failure to vote in

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person or by proxy at the SendGrid special meeting will have no effect on the outcome of the SendGrid compensation proposal and the SendGrid adjournment proposal, (ii) abstentions will be treated as votes cast and, therefore, will have the same effect as a vote against the SendGrid compensation proposal and the SendGrid adjournment proposal, and (iii) broker "non-votes" (if any) will have no effect on the outcome of the SendGrid compensation proposal and SendGrid adjournment proposal. Shares of SendGrid common stock represented by properly executed, timely received and unrevoked proxies will be voted in accordance with the instructions indicated thereon. If you are a SendGrid stockholder of record and you sign and return your proxy card without indicating how to vote on any particular proposal, the shares of SendGrid common stock represented by your proxy will be counted as present for purposes of determining the presence of a quorum for the SendGrid special meeting and will be voted "FOR" that proposal.

Q:

What constitutes a quorum?

A:

Twilio.    The holders of a majority in voting power of the total number shares of Twilio Class A common stock and Twilio Class B common stock issued and outstanding and entitled to vote as of the close of business on the Twilio record date must be present or represented by proxy to constitute a quorum to conduct the Twilio special meeting. All shares of Twilio Class A common stock and Twilio Class B common stock represented at the Twilio special meeting, including abstentions and broker non-votes (shares held by a broker or nominee that are represented at the meeting, but with respect to which the broker or nominee is not instructed by the beneficial owner of such shares to vote on the particular proposal), will be treated as present for purposes of determining the presence or absence of a quorum to conduct the Twilio special meeting.

SendGrid.    The holders of a majority of the voting power of SendGrid's outstanding shares of common stock entitled to vote as of the close of business on the SendGrid record date must be present or represented by proxy to constitute a quorum to conduct the SendGrid special meeting. All shares of SendGrid common stock represented at the SendGrid special meeting, including abstentions and broker non-votes will be counted for purposes of determining the presence or absence of a quorum to conduct the SendGrid special meeting.

A broker non-vote occurs when a broker, bank or other holder of record holding shares for a beneficial owner does not receive voting instructions from the beneficial owner and either chooses not to vote those shares on a routine matter at the stockholders' meeting or is not permitted to vote those shares on a non-routine matter. None of the SendGrid merger proposal, the SendGrid compensation proposal or the SendGrid adjournment proposal is a routine matter. As a result, if you fail to give voting instructions to your broker, bank or other holder of record, your broker, bank or other holder record may not submit or vote your shares for any purpose at the special meeting and, therefore, your shares will not be considered present for purposes of determining a quorum to transact business at the special meeting.

If a SendGrid stockholder submits a proxy card and affirmatively elects to abstain from voting, the shares will be counted as present for purposes of determining the presence of a quorum for the SendGrid special meeting.

If a SendGrid stockholder returns a signed proxy card without indicating voting preferences on such proxy card, the shares of SendGrid common stock represented by that proxy will be counted as present for purposes of determining the presence of a quorum for the SendGrid special meeting.

Q:

What is the difference between a stockholder of record and a "street name" holder?

A:

If your shares are registered directly in your name, you are considered the stockholder of record with respect to those shares. If your shares are held in a stock brokerage account or by a bank,

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trust company or other nominee, then the broker, bank, trust company or other nominee is considered to be the stockholder of record with respect to those shares, while you are considered the beneficial owner of those shares. In the latter case, your shares are said to be held in "street name."

Q:

If I am a beneficial owner of shares held in street name, how do I vote?

A:

If you are not a stockholder of record but instead hold your shares in a stock brokerage account, or if your shares are held by a bank, trust company or other nominee (that is, in street name), you must provide the record holder of your shares with instructions on how to vote your shares. If you are a Twilio stockholder but not a stockholder of record and you do not instruct your broker on how to vote your shares, your broker may not vote your shares on the Twilio stock issuance proposal or any adjournment proposal, which will have no effect on the vote on this proposal, assuming a quorum is present. If you are a SendGrid stockholder but not a stockholder of record and you do not instruct your broker on how to vote your shares, your broker may not vote your shares, which will have the same effect as a vote against the SendGrid merger proposal and, assuming a quorum is present, will have no effect on the outcome of the SendGrid compensation proposal and the SendGrid adjournment proposal.

Please follow the voting instructions provided by your broker or nominee. Please note that you may not vote shares held in street name by returning a proxy card directly to Twilio or SendGrid or by voting in person at your special meeting. Further, brokers who hold shares of Twilio Class A common stock and/or Twilio Class B common stock or SendGrid common stock on behalf of their customers may not give a proxy to Twilio or SendGrid to vote those shares without specific instructions from their customers.

Q:

What will happen if I return my proxy card without indicating how to vote?

A:

If you are a Twilio stockholder of record and you sign and return your proxy card without indicating how to vote on any particular proposal, the shares of Twilio Class A common stock and Twilio Class B common stock represented by your proxy will be counted as present for purposes of determining the presence of a quorum for the Twilio special meeting and will be voted "FOR" that proposal.

If you are a SendGrid stockholder of record and you sign and return your proxy card without indicating how to vote on any particular proposal, the shares of SendGrid common stock represented by your proxy will be counted as present for purposes of determining the presence of a quorum for the SendGrid special meeting and will be voted "FOR" that proposal.

Q:

Can I change my vote after I have returned a proxy or voting instruction card?

A:

Yes. You can change your vote at any time before your proxy is voted at the Twilio special meeting or the SendGrid special meeting, as applicable. You can do this in one of four ways:

•

you can send a signed notice of revocation;

•

you can grant a new, valid proxy bearing a later date;

•

you can vote again by telephone or the Internet at a later time; or

•

if you are a holder of record, you can attend the special meeting and vote in person, which will automatically cancel any proxy previously given, or you may revoke your proxy in person, but your attendance alone will not revoke any proxy that you have previously given.

If you choose either of the first two methods, you must provide your notice of revocation or your new proxy to the Secretary of Twilio or Secretary of SendGrid, as applicable, prior to your shares

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being voted. If your shares are held in street name by your broker or nominee, you should contact them to change your vote.

Q:

What should I do if I receive more than one set of voting materials?

A:

Please vote each proxy card and voting instruction card that you receive. You 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 cards. For example, stockholders who hold shares in more than one brokerage account will receive a separate voting instruction card for each brokerage account in which shares are held. If shares are held in more than one name, stockholders will receive more than one proxy or voting instruction card. In addition, if you are a stockholder of both Twilio and SendGrid, you may receive one or more proxy cards or voting instruction cards for Twilio and one or more proxy cards or voting instruction cards for SendGrid. If you are a stockholder of both Twilio and SendGrid, please note that a vote for the issuance of shares of Twilio Class A common stock in the merger pursuant to the terms of the merger agreement for the Twilio special meeting will not constitute a vote for the proposal to adopt the merger agreement for the SendGrid special meeting, and vice versa. Therefore, please vote each proxy and voting instruction card you receive, whether from Twilio or SendGrid.

Q:

Is there a list of stockholders entitled to vote at the Twilio and SendGrid special meetings?

A:

The names of stockholders of record entitled to vote at the Twilio special meeting will be available at the Twilio special meeting and for 10 days prior to the Twilio special meeting for any purpose germane to the special meeting, between the hours of 9:00 a.m. and 4:30 p.m., at Twilio's principal executive offices located at 375 Beale Street, Suite 300, San Francisco, California 94105, or by contacting Twilio's corporate secretary.

The names of stockholders of record entitled to vote at the SendGrid special meeting will be available at the SendGrid special meeting and for 10 days prior to the SendGrid special meeting for any purpose germane to the special meeting, between the hours of 9:00 a.m. and 4:30 p.m., at SendGrid's principal executive offices located at 1801 California Street, Suite 500, Denver, Colorado 80202, or by contacting SendGrid's corporate secretary.

Q:

What happens if I am a SendGrid stockholder who sells my shares of SendGrid common stock before the SendGrid special meeting?

A:

The record date for the SendGrid special meeting is earlier than the SendGrid special meeting. If you transfer your shares of SendGrid common stock after the SendGrid record date but before the SendGrid special meeting, you will retain your right to vote at the SendGrid special meeting, but will have transferred the right to receive the merger consideration in the merger. In order to receive the merger consideration, you must hold your shares through the effective time of the merger.

Q:

What happens if I am a Twilio stockholder who sells my shares of Twilio Class A common stock and/or Twilio Class B common stock before the Twilio special meeting?

A:

The record date for the Twilio special meeting is earlier than the Twilio special meeting. If you transfer your shares of Twilio Class A common stock and/or Twilio Class B common stock after the Twilio record date but before the Twilio special meeting, you will retain your right to vote at the Twilio special meeting.

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Q:

What will happen to my SendGrid stock options and/or restricted stock units at the time of the merger?

A:

Treatment of Restricted Stock Unit Awards.    At the effective time of the merger, each SendGrid restricted stock unit outstanding immediately prior to such time, which we refer to as a SendGrid RSU, whether vested or issuable, other than those held by a current or former non-employee director of SendGrid, will be assumed by Twilio and converted into a restricted stock unit for a number of shares of Twilio Class A common stock which we refer to as an assumed RSU equal to the product of (i) the number of shares of SendGrid common stock subject to such SendGrid RSU and (ii) the exchange ratio (rounded down to the nearest whole share). Except for the change to the number and type of shares, each assumed RSU will be subject to the same terms and conditions, including vesting, as were applicable to such SendGrid RSU prior to the merger. At the effective time of the merger, each outstanding SendGrid RSU held by a current or former non-employee director of SendGrid will be cancelled and converted into a right to receive a number of fully-vested shares of Twilio Class A common stock equal to the product of (a) the number of shares of SendGrid common stock subject to such SendGrid RSU and (b) the exchange ratio (rounded down to the nearest whole share).

Treatment of Stock Options.    At the effective time of the merger, each option to purchase SendGrid common stock that is outstanding and unexercised immediately prior to such time, which we refer to as a SendGrid option, whether vested or unvested (other than (i) any SendGrid option held by a former employee or former service provider of SendGrid, or subsidiary of SendGrid and (ii) any SendGrid option granted to certain holders in the UK, which we refer to as a SendGrid UK option) will be assumed by Twilio and converted into an option to acquire a number of shares of Twilio Class A Common Stock, which we refer to as an adjusted option, equal to the product of (a) the number of shares of SendGrid common stock subject to such SendGrid option and (b) the exchange ratio (rounded down to the nearest whole share). The per share exercise price of each adjusted option will be equal to (1) the per share exercise price of such SendGrid option immediately prior to the merger divided by (2) the exchange ratio (with the resulting price per share rounded up to the nearest whole cent). Except for the changes made to the number and type of shares and the exercise price, each adjusted option will be subject to the same terms and conditions, including vesting, as were applicable to such SendGrid option immediately prior to the merger. At the effective time of the merger, (A) each unvested SendGrid option that is outstanding and unexercised as of immediately prior to such time and held by a former employee or former service provider of SendGrid or a subsidiary of SendGrid will be cancelled without the payment of any consideration, and (B) each vested SendGrid option that is outstanding and unexercised as of immediately prior to such time and held by a former employee or former service provider of SendGrid or a subsidiary of SendGrid together with all outstanding and unexercised SendGrid UK options (provided the holder of such SendGrid options agrees) will be cancelled and converted into a right to receive a number of shares of Twilio Class A common stock equal to the product of (x) the number of shares of SendGrid common stock subject to such SendGrid option multiplied by the excess, if any, of (I) the SendGrid Share Value over (II) the per share exercise price for shares subject to such SendGrid option, divided by (y) the SendGrid Share Value, multiplied by (z) the exchange ratio (rounded down to the nearest whole share). The "SendGrid Share Value" means the volume weighted average closing sale price of one share of SendGrid common stock as reported on the NYSE for the 5 consecutive trading days ending on the trading day immediately preceding the effective time of the merger (as adjusted to reflect any stock splits, stock dividends, combinations, reorganizations, reclassifications or similar events).

Treatment of ESPP.    Following the date of the merger agreement, SendGrid has taken actions with respect to SendGrid's 2017 Employee Stock Purchase Plan, which we refer to as the ESPP, to provide that with respect to any offering periods in effect as of the date of the merger agreement,

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which we refer to as the current purchase period, (i) no employee who is not a participant in the ESPP as of the date of the merger agreement may become a participant in the ESPP, and (ii) no employee participating in the current purchase period may increase his or her payroll contribution rate pursuant to the ESPP from the rate in effect immediately prior to the date of the merger agreement, except as required by applicable law. In addition, (a) the current purchase period will end on March 4, 2019, provided that if the effective time of the merger is prior to March 4, 2019, SendGrid will end the current purchase period on a specified trading day occurring at least 10 days prior to the date on which the effective time of the merger is expected to occur; (b) there will be no offering periods following the current purchase period and (c) in all events, SendGrid shall terminate the ESPP prior to the effective time of the merger.

Q:

How will the rights of SendGrid stockholders change after the merger?

A:

SendGrid stockholders will receive shares of Twilio Class A common stock in connection with the merger and will no longer be stockholders of SendGrid following the merger. Their rights as holders of Twilio Class A common stock will be governed by the amended and restated certificate of incorporation of Twilio and Twilio's amended and restated bylaws. For additional information on stockholder rights, see "Comparison of Rights of Twilio Stockholders and SendGrid Stockholders" beginning on page 185 of this joint proxy statement/prospectus.

The rights of Twilio stockholders will remain the same as prior to the merger.

Q:

What are the material U.S. federal income tax consequences of the merger to U.S. holders of SendGrid common stock?

A:

It is intended that, for U.S. federal income tax purposes, the merger will qualify as a "reorganization" within the meaning of Section 368(a) of the U.S. Internal Revenue Code of 1986, as amended, which we refer to as the Code. If the merger qualifies for such intended tax treatment, a U.S. holder of SendGrid common stock will not recognize any gain or loss for U.S. federal income tax purposes upon the exchange of such holder's shares of SendGrid common stock for shares of Twilio Class A common stock in the merger, except that such holder of SendGrid common stock may recognize gain or loss with respect to cash received in lieu of a fractional share of Twilio Class A common stock.

As further described in the section entitled "The Merger Agreement—Conditions to Completion of the Merger", (i) SendGrid's obligation to effect the merger is subject to the satisfaction, or waiver by SendGrid, at or prior to the effective time of the merger, of the condition that SendGrid receive a written tax opinion from Cooley LLP, legal counsel to SendGrid, dated as of the closing date of the merger, to the effect that the merger will qualify as a "reorganization" within the meaning of Section 368(a) of the Code and (ii) Twilio's obligation to effect the merger is subject to the satisfaction, or waiver by Twilio, at or prior to the effective time of the merger, of the condition that Twilio receive a written tax opinion from Goodwin Procter LLP, legal counsel to Twilio, dated as of the closing date of the merger, to the effect that the merger will qualify as a "reorganization" within the meaning of Section 368(a) of the Code. In the event that Cooley LLP does not render such tax opinion, and SendGrid does not otherwise waive this condition, the condition may be satisfied if another nationally recognized law firm proposed by Twilio and that is reasonably acceptable to SendGrid renders such tax opinion. In the event that Goodwin Procter LLP does not render such tax opinion, and Twilio does not otherwise waive this condition, the condition may be satisfied if another nationally recognized law firm proposed by SendGrid and that is reasonably acceptable to Twilio renders such tax opinion.

You should read the section entitled "Material U.S. Federal Income Tax Consequences" beginning on page 149 for a more complete discussion of the U.S. federal income tax consequences of the

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merger. Tax matters can be complicated, and the tax consequences of the merger to you will depend on your particular situation. You should consult your tax advisor to determine the tax consequences of the merger to you.

Q:

Are there any risks that I should consider in deciding how to vote?

A:

Yes. You should read and carefully consider the risk factors set forth in the section entitled "Risk Factors" beginning on page 36 of this joint proxy statement/prospectus. You also should read and carefully consider the risk factors of Twilio and SendGrid contained in the documents that are incorporated by reference into this joint proxy statement/prospectus.

Q:

What happens if the merger is not completed?

A:

If the merger is not completed for any reason, SendGrid stockholders will not receive the merger consideration payable or issuable under the merger agreement. Instead, Twilio and SendGrid will remain separate public companies, and SendGrid expects that its common stock will continue to be registered under the Exchange Act and traded on the NYSE. In specified circumstances, either Twilio or SendGrid may be required to pay to the other party a termination fee or reimburse the other party's transaction expenses, as described below.

Q:

Does SendGrid have to pay anything to Twilio if the SendGrid merger proposal is not approved by the SendGrid stockholders or if the merger agreement is otherwise terminated?

A:

If the SendGrid stockholders do not adopt the merger agreement at the SendGrid special meeting and the merger agreement is terminated by Twilio, SendGrid must reimburse Twilio's reasonable and documented out-of-pocket expenses up to $5 million.

In certain circumstances, depending on the reasons for termination of the merger agreement, SendGrid may have to pay Twilio a termination fee of $69 million. For a discussion of the circumstances under which a termination fee is payable by SendGrid or the requirement to reimburse expenses applies, see "The Merger Agreement—Termination Fees and Expenses; Liability for Breach."

Q:

Does Twilio have to pay anything to SendGrid if the Twilio stock issuance proposal is not approved by the Twilio stockholders or if the merger agreement is otherwise terminated?

A:

If the Twilio stockholders do not approve the issuance of the shares of Twilio Class A common stock to be issued to SendGrid stockholders in the merger at the Twilio special meeting and the merger agreement is terminated by SendGrid, Twilio must reimburse SendGrid's reasonable and documented out-of-pocket expenses up to $5 million. Further, if the merger agreement is terminated for failure to obtain the approval of the Twilio stockholders of the Twilio stock issuance proposal and the shares of Twilio Class B common stock subject to irrevocable proxies fail to be voted in favor of the issuance of the Twilio stock issuance proposal, Twilio will be required to pay a termination fee of $120 million.

In other specified circumstances, depending on the reasons for termination of the merger agreement, Twilio may have to pay SendGrid a termination fee of $120 million. For a discussion of the circumstances under which a termination fee is payable by Twilio or the requirement to reimburse expenses applies, see "The Merger Agreement—Termination Fees and Expenses; Liability for Breach"

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Q:

When do you expect the merger to be completed?

A:

SendGrid and Twilio intend to complete the merger as soon as reasonably practicable and currently anticipate the closing of the merger to occur in the first half of 2019, following the satisfaction of all the conditions to completion of the merger. However, the merger is subject to various regulatory clearances and the satisfaction or waiver of other conditions and it is possible that factors outside the control of SendGrid and Twilio could result in the merger being completed at a later time or not at all. There can be no assurances as to when or if the merger will close. See "The Merger Agreement—Conditions to Completion of the Merger."

Q:

What do I need to do now?

A:

You should carefully read and consider the information contained in and incorporated by reference into this joint proxy statement/prospectus, including its annexes. Even if you plan to attend the Twilio special meeting or the SendGrid special meeting in person, after carefully reading and considering the information contained in this joint proxy statement/prospectus, please vote promptly to ensure that your shares are represented at the Twilio special meeting or the SendGrid special meeting, as applicable.

Q:

Do I need to do anything with my SendGrid common stock certificates now?

A:

No. After the merger is completed, if you held certificates representing shares of SendGrid common stock prior to the merger, Twilio's exchange agent, which we refer to as the exchange agent, will send you a letter of transmittal and instructions for exchanging your shares of SendGrid common stock for the merger consideration. Upon surrender of the certificates for cancellation along with the executed letter of transmittal and other required documents described in the instructions, a SendGrid stockholder will receive the merger consideration. The shares of Twilio Class A common stock you receive in the merger will be issued in book-entry form.

If you are a Twilio stockholder, you are not required to take any action with respect to your Twilio stock certificates.

Q:

Do I need to do anything with my SendGrid common stock held in book-entry form now?

A:

No. After the merger is completed, if you held shares of SendGrid common stock in book-entry form prior to the merger, Twilio's exchange agent will send you a letter of transmittal and instructions for exchanging your shares of SendGrid common stock for the merger consideration. Upon receipt of an agent's message in customary form (or such other evidence, if any, as the exchange agent may reasonably request), along with the executed letter of transmittal and other required documents described in the instructions, a SendGrid stockholder will receive the merger consideration. The shares of Twilio Class A common stock you receive in the merger will be issued in book-entry form.

Q:

Do I need identification to attend the Twilio or SendGrid special meeting in person?

A:

Yes. Please bring proper identification, together with proof that you are a record owner of Twilio common stock or SendGrid common stock, as applicable. If your shares are held in street name, please bring acceptable proof of ownership, such as a letter from your broker or an account statement stating or showing that you beneficially owned shares of Twilio or SendGrid stock, as applicable, on the record date for the applicable special meeting.

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Q:

Why are SendGrid stockholders being asked to cast an advisory (non-binding) vote to approve the SendGrid compensation proposal?

A:

The Exchange Act and applicable SEC rules thereunder require SendGrid to seek an advisory (non-binding) vote with respect to certain payments that could become payable to its named executive officers in connection with the merger.

Q:

What will happen if the SendGrid stockholders do not approve the SendGrid compensation proposal at the SendGrid special meeting?

A:

Approval of the SendGrid compensation proposal is not a condition to completion of the merger. The vote with respect to the SendGrid compensation proposal is an advisory vote and will not be binding on either Twilio or SendGrid. Therefore, if the other requisite stockholder approvals are obtained and the merger is completed, the amounts payable under the SendGrid compensation proposal will continue to be payable to SendGrid's named executive officers in accordance with the terms and conditions of the applicable agreements.

Q:

Are stockholders entitled to appraisal rights?

A:

Under Delaware law, the SendGrid stockholders are not entitled to appraisal rights in connection with the SendGrid merger proposal.

Under Delaware law, the Twilio stockholders are not entitled to appraisal rights in connection with the Twilio stock issuance proposal.

Q:

How can I contact Twilio's or SendGrid's transfer agent?

A:

You may contact Twilio's transfer agent by writing Computershare Trust Company, N.A., 250 Royall Street, Canton, Massachusetts 02021, by telephoning (800) 736-3001, or via its Investor Centre at www.computershare.com/investor.

You may contact SendGrid's transfer agent by writing Broadridge Corporate Issuer Solutions, Inc., 1717 Arch St., Suite 1300, Philadelphia, Pennsylvania 19103, by telephoning (877) 830-4936, or (720) 378-5591.

Q:

Who should I contact if I have any questions about the proxy materials or about voting?

A:

If you have any questions about the proxy materials or if you need assistance submitting your proxy or voting your shares or need additional copies of this joint proxy statement/prospectus or the enclosed proxy card, you should, if you are a Twilio stockholder, contact Twilio's proxy solicitor, Innisfree M&A Incorporated, 501 Madison Avenue, 20th Floor, New York, New York 10022, banks and brokers call collect: (212) 750-5833, stockholders call toll free: (888) 750-5834, and, if you are a SendGrid stockholder, contact MacKenzie Partners, Inc., SendGrid's proxy solicitor, by telephone toll-free at (800) 322-2885, by email at proxy@mackenziepartners.com, or by mail at MacKenzie Partners, Inc., 1407 Broadway, 27th Floor, New York, New York 10018.

Q:

Who is the exchange agent in the merger?

A:

Computershare Trust Company, N.A. will be the exchange agent for the merger.

Q:

Where can I find more information about Twilio and SendGrid?

A:

You can find more information about Twilio and SendGrid from the various sources described under "Where You Can Find More Information" beginning on page 199 of this joint proxy statement/prospectus.

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