DEFM14A 1 a2237381zdefm14a.htm DEFM14A

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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.          )

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Soliciting Material under §240.14a-12

 

SendGrid, Inc.

(Name of Registrant as Specified In Its Charter)

 

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MERGER PROPOSAL—YOUR VOTE IS VERY IMPORTANT

LOGO   LOGO

          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,

GRAPHIC

Jeff Lawson
Chief Executive Officer, Director and Chairman
Twilio Inc.

 

GRAPHIC

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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LOGO

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,

 

 

GRAPHIC

 

 

Jeff Lawson
Chief Executive Officer

 

 

San Francisco, California

 

 

December 18, 2018

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LOGO

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,

 

 

GRAPHIC

 

 

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:

Twilio Inc.   SendGrid, Inc.

375 Beale Street, Suite 300
San Francisco, California 94105
(415) 390-2337
Attn: Investor Relations

 

1801 California Street, Suite 500
Denver, CO 80202
(888) 985-7363
Attn: Investor Relations

        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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  Page  

QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE SPECIAL MEETING

    1  

SUMMARY

   
15
 

Parties to the Merger

    15  

Risk Factors

    17  

The Merger and the Merger Agreement

    17  

Twilio's Reasons for the Merger; Recommendation of the Twilio Board

    19  

SendGrid's Reasons for the Merger; Recommendation of the SendGrid Board

    19  

Voting Agreements

    20  

Opinion of Twilio's Financial Advisor, Goldman Sachs & Co. LLC

    20  

Opinion of SendGrid's Financial Advisor, Morgan Stanley & Co. LLC

    21  

The Merger Agreement

    21  

Regulatory Approvals Required for the Merger

    23  

Accounting Treatment

    24  

Appraisal Rights

    24  

SendGrid's Executive Officers and Directors Have Financial Interests in the Merger That Differ from the Interests of SendGrid Stockholders

    24  

Rights of SendGrid Stockholders Will Change as a Result of the Merger

    25  

The Twilio Special Meeting

    25  

The SendGrid Special Meeting

    26  

SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA OF TWILIO

   
27
 

SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA OF SENDGRID

   
30
 

SELECTED UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL DATA

   
33
 

COMPARATIVE HISTORICAL AND UNAUDITED PRO FORMA PER SHARE DATA

   
33
 

COMPARATIVE STOCK PRICE DATA AND DIVIDENDS

   
35
 

RISK FACTORS

   
36
 

Risk Factors Relating to the Merger

    36  

Risk Factors Relating to Twilio Following the Merger

    43  

Other Risks

    45  

Other Risks Related to Twilio's Business and SendGrid's business

    47  

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

   
48
 

THE TWILIO SPECIAL MEETING

   
50
 

Date, Time and Place of the Twilio Special Meeting

    50  

Purpose of the Twilio Special Meeting

    50  

Recommendation of the Twilio Board

    50  

Record Date for the Twilio Special Meeting; Stock Entitled to Vote

    50  

Solicitation of Proxies; Revocability of Proxies

    51  

Quorum

    51  

Vote Required

    51  

Twilio Voting Agreements

    52  

Abstentions and Broker Non-Votes

    52  

Voting Power of Twilio's Directors and Executive Officer

    52  

Attending the Twilio Special Meeting

    52  

Voting of Proxies by Record Stockholders

    53  

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  Page  

Shares Held in Street Name

    54  

Revocability of Proxies and Changes to a Twilio Stockholder's Vote

    54  

Adjournments

    55  

Postponements

    55  

Stockholder List

    55  

Tabulation of Votes

    55  

How You Can Reduce the Number of Copies of Twilio's Proxy Materials You Receive

    56  

Assistance

    56  

TWILIO PROPOSALS

   
57
 

Twilio Proposal 1: The Twilio Stock Issuance Proposal

    57  

Twilio Proposal 2: The Twilio Adjournment Proposal

    57  

THE SENDGRID SPECIAL MEETING

   
59
 

Date, Time and Place of the SendGrid Special Meeting

    59  

Purpose of the SendGrid Special Meeting

    59  

Recommendation of the SendGrid Board

    59  

Record Date for the SendGrid Special Meeting; Stock Entitled to Vote

    59  

Solicitation of Proxies; Revocability of Proxies

    60  

Quorum

    60  

Vote Required

    61  

SendGrid Voting Agreements

    61  

Abstentions and Broker Non-Votes

    61  

Voting Power of SendGrid's Directors and Executive Officers

    61  

Attending the SendGrid Special Meeting

    62  

Voting of Proxies by Record Stockholders

    62  

Shares Held in Street Name

    63  

Revocability of Proxies and Changes to a SendGrid Stockholder's Vote

    63  

Adjournments

    64  

Stockholder List

    64  

Tabulation of Votes

    64  

How You Can Reduce the Number of Copies of SendGrid's Proxy Materials You Receive

    64  

Assistance

    65  

SENDGRID PROPOSALS

   
66
 

SendGrid Proposal 1: The SendGrid Merger Proposal

    66  

SendGrid Proposal 2: The SendGrid Compensation Proposal

    66  

SendGrid Proposal 3: The SendGrid Adjournment Proposal

    67  

THE MERGER AGREEMENT

   
68
 

Terms of the Merger; Merger Consideration

    69  

Procedures for Exchanging SendGrid Common Stock in the Merger

    69  

Completion of the Merger

    70  

Representations and Warranties

    70  

Conduct of Business

    72  

No Solicitation of Alternative Proposals

    77  

Changes in Board Recommendations

    79  

Efforts to Obtain Required Stockholder Votes

    80  

Efforts to Complete the Merger

    82  

SendGrid Employee Benefits Matters

    82  

Indemnification and Insurance

    83  

Treatment of SendGrid Equity Awards

    83  

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  Page  

Other Covenants and Agreements

    84  

Conditions to Completion of the Merger

    85  

Termination of the Merger Agreement

    88  

Termination Fees and Expenses; Liability for Breach

    89  

Amendments and Waivers

    90  

Specific Performance

    90  

THE VOTING AGREEMENTS

   
91
 

Twilio Voting Agreements

    91  

SendGrid Voting Agreements

    92  

THE MERGER

   
95
 

Background of the Merger

    95  

Twilio's Reasons for the Merger; Recommendation of the Stock Issuance by the Twilio Board

    105  

SendGrid's Reasons for the Merger; Recommendation of the Merger by the SendGrid Board

    107  

Certain Unaudited Prospective Financial Information Prepared by Twilio Management

    110  

Opinion of Twilio's Financial Advisor, Goldman Sachs & Co. LLC

    113  

Certain Unaudited Prospective Financial Information Prepared by SendGrid Management

    120  

Opinion of SendGrid's Financial Advisor, Morgan Stanley & Co. LLC

    126  

Financial Interests of Twilio Directors and Executive Officers in the Merger

    139  

Financial Interests of SendGrid Directors and Executive Officers in the Merger

    140  

Quantification of Potential Payments to SendGrid Named Executive Officers in Connection with the Merger

    145  

Regulatory Approvals Required for the Merger

    147  

Listing of Twilio Class A Common Stock

    147  

Delisting and Deregistration of SendGrid Common Stock

    147  

Appraisal Rights

    148  

Litigation Related to the Merger

    148  

MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES

   
149
 

U.S. Federal Income Tax Consequences of the Merger

    150  

Information Reporting and Backup Withholding

    152  

ACCOUNTING TREATMENT

   
153
 

UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS

   
154
 

Unaudited Pro Forma Condensed Combined Balance Sheet

    155  

Unaudited Pro Forma Condensed Combined Statement of Operations

    156  

Unaudited Pro Forma Condensed Combined Statement of Operations

    157  

Notes to Unaudited Pro Forma Condensed Combined Financial Statements

    158  

PRINCIPAL STOCKHOLDERS OF TWILIO

   
172
 

PRINCIPAL STOCKHOLDERS OF SENDGRID

   
176
 

DESCRIPTION OF CAPITAL STOCK

   
180
 

General

    180  

Common Stock

    180  

Preferred Stock

    181  

Registration Rights

    181  

Anti-Takeover Provisions

    182  

COMPARISON OF RIGHTS OF TWILIO STOCKHOLDERS AND SENDGRID STOCKHOLDERS

   
185
 

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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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SUMMARY

        This summary highlights selected information contained elsewhere in this joint proxy statement/prospectus and may not contain all the information that is important to you with respect to the merger and the related matters being considered at the applicable special meeting. Twilio and SendGrid urge you to read carefully the remainder of this joint proxy statement/prospectus, including the annexes and exhibits attached to and the documents incorporated by reference into this joint proxy statement/prospectus. For a description of, and instructions as to how to obtain, this information, see "Where You Can Find More Information" beginning on page 199 of this joint proxy statement/prospectus. Certain items in this summary include a page reference directing you to a more complete description of that item.

Parties to the Merger

Twilio Inc.

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

        Twilio was incorporated in the state of Delaware on March 13, 2008. It is the leader in the Cloud Communications Platform category and enables developers to build, scale, and operate real-time communications within their software applications via simple-to-use Application Programming Interfaces, which we refer to as API. The power, flexibility, and reliability offered by Twilio's software building blocks empower companies of virtually every shape and size to build world-class engagement into their customer experience.

        Twilio's platform consists of three layers: the Engagement Cloud, Programmable Communications Cloud and Super Network. The Engagement Cloud software is a set of APIs that handles the higher level communication logic needed for nearly every type of customer engagement. These APIs are focused on the business challenges that a developer is looking to address, allowing Twilio's customers to more quickly and easily build better ways to engage with their customers throughout their journey. Twilio's Programmable Communications Cloud software is a set of APIs that enables developers to embed voice, messaging and video capabilities into their applications. The Programmable Communications Cloud is designed to support almost all the fundamental ways humans communicate, unlocking innovators to address just about any communication market. The Super Network is Twilio's software layer that allows its customers' software to communicate with connected devices globally. It interconnects with communications networks around the world and continually analyzes data to optimize the quality and cost of communications that flow through Twilio's platform. The Super Network also contains a set of APIs that gives Twilio's customers access to more foundational components of its platform, like phone numbers.

        As of September 30, 2018, Twilio's customers' applications that are embedded with Twilio products could reach users via voice, messaging and video in nearly every country in the world, and its platform offered customers local telephone numbers in over 100 countries and text-to-speech functionality in 26 languages. Twilio supports its global business through 27 cloud data centers in nine regions around the world and has developed contractual relationships with network service providers globally.

        Its business model is primarily focused on reaching and serving the needs of software developers, who Twilio believes are becoming increasingly influential in technology decisions in a wide variety of companies. Twilio calls this approach its Business Model for Innovators, which empowers developers by reducing friction and upfront costs, encouraging experimentation, and enabling developers to grow as customers as their ideas succeed. Twilio established and maintains its leadership position by engaging directly with, and cultivating, its developer community, which has led to the rapid adoption of the Twilio platform. Twilio reaches developers through community events and conferences, including its

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SIGNAL developer conferences, to demonstrate how every developer can create differentiated applications incorporating communications using Twilio products.

        This joint proxy statement/prospectus incorporates important business and financial information about Twilio from other documents that are not included in or delivered with this joint proxy statement/prospectus. For a list of the documents that are incorporated by reference, see "Where You Can Find More Information" beginning on page 199 of this joint proxy statement/prospectus.

Topaz Merger Subsidiary, Inc.

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

        Topaz Merger Subsidiary, Inc., a direct wholly owned subsidiary of Twilio, is a Delaware corporation formed on October 12, 2018 for the purpose of effecting the merger. Upon completion of the merger, Merger Sub will be merged with and into SendGrid, with SendGrid continuing as a direct wholly owned subsidiary of Twilio.

        Merger Sub has not conducted any activities other than those incidental to its formation and the matters contemplated by the merger agreement, including the preparation of applicable regulatory filings in connection with the merger.

SendGrid, Inc.

    1801 California Street, Suite 500
    Denver, CO 80202
    (888) 985-7363

        SendGrid is a leading digital communication platform, enabling businesses to engage with their customers via email reliably, effectively and at scale. Its cloud-based platform allows for frictionless adoption and immediate value creation for businesses, providing their developers and marketers with the tools to seamlessly and effectively reach their customers using email. Since its inception, SendGrid has processed more than one trillion emails.

        SendGrid offers its customers three services: Email API; Marketing Campaigns; and Expert Services. Its Email API service allows developers to use its API in their preferred development framework to leverage its platform to add email functionality to their applications within minutes. This service enables businesses to send thousands or billions of emails, all with the same high level of service and reliability, and incorporates proprietary technology and domain expertise to significantly improve deliverability rates. Its Marketing Campaigns service allows marketers to upload and manage customer contact lists, create and test email templates, and then execute and analyze multi-faceted email campaigns that engage customers and drive growth. Its Expert Services help businesses further optimize their email delivery. With SendGrid's platform, businesses can achieve industry leading email deliverability that translates into higher brand engagement with their customers.

        SendGrid's category leadership, self-service model and company culture have enabled it to attract and retain customers and employees, and continue to develop innovative solutions for email delivery. It delivers its services through a self-service cloud-based subscription model, where businesses primarily sign up for its services through its website. SendGrid offers transparent and affordable pricing, generally on a per month basis by volume of email and typically paid by credit card. In addition, it has robust documentation for onboarding and ongoing usage. This self-service delivery model has enabled it to rapidly attract customers while operating its business efficiently.

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        This joint proxy statement/prospectus incorporates important business and financial information about SendGrid from other documents that are not included in or delivered with this joint proxy statement/prospectus. For a list of the documents that are incorporated by reference, see "Where You Can Find More Information" beginning on page 199 of this joint proxy statement/prospectus.

Risk Factors

        Before voting at the Twilio special meeting or the SendGrid special meeting, you should carefully consider all of the information contained in or as incorporated by reference into this joint proxy statement/prospectus, as well as the specific factors under the heading "Risk Factors" beginning on page 36 of this joint proxy statement/prospectus.

The Merger and the Merger Agreement

        A copy of the merger agreement is attached as Annex A to this joint proxy statement/prospectus. Twilio and SendGrid encourage you to read the entire merger agreement carefully because it is the principal document governing the merger. For more information on the merger agreement, see the section entitled "The Merger Agreement" beginning on page 68 of this joint proxy statement/prospectus.

    Effects of the Merger; Merger Consideration

        If the conditions set forth in the merger agreement are satisfied or waived, Merger Sub will merge with and into SendGrid. SendGrid will survive the merger and will continue as a direct wholly owned subsidiary of Twilio.

        In the merger, each share of SendGrid common stock issued and outstanding immediately prior to the effective time of the merger will be automatically converted at the effective time into the right to receive 0.485 of a share of Twilio Class A common stock, 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. Twilio stockholders will not receive any merger consideration and will continue to hold their existing shares of Twilio Class A common stock and/or Twilio Class B common stock.

    Treatment of SendGrid Equity Awards (See page 83)

        Treatment of Restricted Stock Unit Awards.    At the effective time of the merger, each SendGrid RSU outstanding immediately prior to such time, 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 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 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 UK option) will be assumed by Twilio and converted into 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

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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).

        Treatment of ESPP.    Following the date of the merger agreement, SendGrid has taken actions with respect to the ESPP to provide that with respect to 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.

    Material U.S. Federal Income Tax Consequences of the Merger (See page 149)

        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 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

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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.

        The discussion of U.S. federal income tax consequences of the merger contained in this proxy statement/prospectus is intended to provide only a general summary and is not a complete analysis or description of all potential U.S. federal income tax consequences of the merger. The discussion does not address tax consequences that may vary with, or are contingent on, individual circumstances. In addition, it does not address the effects of any non-U.S., state or local tax laws.

        For a more complete discussion of the material U.S. federal income tax consequences of the merger, please carefully review the information set forth in the section entitled "Material U.S. Federal Income Tax Consequences".

        The tax consequences of the merger to any particular stockholder will depend on that stockholder's particular facts and circumstances. Accordingly, you are urged to consult your own tax advisor as to the specific tax consequences of the merger, including the effects of U.S. federal, state, local, non-U.S. and other tax laws.

Twilio's Reasons for the Merger; Recommendation of the Twilio Board (See page 105)

        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, including the issuance of Twilio Class A common stock in connection with the merger. 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.

        For the factors considered by the Twilio Board in reaching its decision to approve the merger agreement, see the section entitled "The Merger—Twilio's Reasons for the Merger; Recommendation of the Stock Issuance by the Twilio Board" beginning on page 105.

        The Twilio Board recommends that Twilio stockholders vote "FOR" the proposal to issue shares of Twilio Class A common stock in connection with the merger and "FOR" the Twilio adjournment proposal.

SendGrid's Reasons for the Merger; Recommendation of the SendGrid Board (See page 107)

        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 recused himself from all deliberations due to his concurrent service as a director of Twilio.

        For the factors considered by the SendGrid Board in reaching its decision to approve the merger agreement, see the section entitled "The Merger—SendGrid's Reasons for the Merger; Recommendation of the Merger by the SendGrid Board" beginning on page 107 of this joint proxy statement/prospectus.

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

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Voting Agreements (See page 91)

        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.

Opinion of Twilio's Financial Advisor, Goldman Sachs & Co. LLC (See page 113)

        Twilio retained Goldman Sachs & Co. LLC, which we refer to as Goldman Sachs, as its financial advisor in connection with the merger. Goldman Sachs rendered its oral opinion to the Twilio Board on October 15, 2018, subsequently confirmed in writing by delivery of a written opinion of such date, that, as of such date and based upon and subject to the factors and assumptions set forth therein, the exchange ratio pursuant to the merger agreement was fair from a financial point of view to Twilio.

        The full text of the written opinion of Goldman Sachs, dated October 15, 2018, which sets forth assumptions made, procedures followed, matters considered and limitations on the review undertaken in connection with the opinion, is attached as Annex B to this joint proxy statement/prospectus. Goldman Sachs provided advisory services and its opinion for the information and assistance of the Twilio Board in connection with its consideration of the merger. The Goldman Sachs opinion is not a recommendation as to how any Twilio stockholder should vote with respect to the issuance of Twilio Class A common stock in connection with the merger or any other matter. For a description of the opinion that the Twilio Board received from Goldman Sachs, see the section entitled "The Merger—Opinion of Twilio's Financial Advisor, Goldman Sachs & Co. LLC" beginning on page 113.

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Opinion of SendGrid's Financial Advisor, Morgan Stanley & Co. LLC (See page 126)

        SendGrid retained Morgan Stanley & Co. LLC, which we refer to as Morgan Stanley, as its financial advisor in connection with the merger. Morgan Stanley rendered an oral opinion to the SendGrid Board on October 15, 2018, subsequently confirmed by delivery of a written opinion dated as of such date, that as of such date and based upon and subject to the assumptions made, procedures followed, matters considered and qualifications and limitations on the scope of review undertaken by Morgan Stanley as set forth in its written opinion, the exchange ratio pursuant to the merger agreement was fair from a financial point of view to the holders of shares of SendGrid common stock (other than the Excluded Shares (as defined in Morgan Stanley's written opinion)). The full text of Morgan Stanley's written opinion, dated October 15, 2018, is attached as Annex C to this joint proxy statement/prospectus and is incorporated by reference in this joint proxy statement/prospectus in its entirety. The description of Morgan Stanley's opinion set forth below is qualified in its entirety by reference to the full text of Morgan Stanley's opinion. Morgan Stanley's opinion was directed to the SendGrid Board, in its capacity as such, and addressed only the fairness from a financial point of view of the exchange ratio pursuant to the merger agreement to the holders of shares of SendGrid common stock (other than the Excluded Shares) as of the date of the opinion. It did not address any other aspects or implications of the merger or in any manner address the prices at which the Twilio Class A common stock would trade following consummation of the merger or at any time and was not intended to and did not express any opinion or recommendation as to how the stockholders of Twilio or SendGrid should vote at the stockholders' meetings to be held in connection with the merger.

        For a description of the opinion that the SendGrid Board received from Morgan Stanley, see "The Merger—Opinion of SendGrid's Financial Advisor, Morgan Stanley & Co. LLC" beginning on page 126 of this joint proxy statement/prospectus.

The Merger Agreement (See page 68)

        The terms and conditions of the merger are contained in the merger agreement, which is attached to this joint proxy statement/prospectus as Annex A. You should read the merger agreement carefully, as it is the legal document that governs the merger.

    Conditions to Completion of the Merger (See page 85)

        As more fully described in this joint proxy statement/prospectus and in the merger agreement, the completion of the merger depends on a number of conditions being satisfied or, where legally permissible, waived. These conditions include, among others, receipt of the requisite approvals by Twilio stockholders and SendGrid stockholders, the expiration or early termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, which we refer to as the HSR Act, the absence of any law or order prohibiting the merger, the shares of Twilio Class A common stock to be issued in connection with the merger having been approved for listing on the NYSE, the effectiveness of the registration statement of which this joint proxy statement/prospectus forms a part, the correctness of all representations and warranties made by the parties in the merger agreement and performance by the parties of their obligations under the merger agreement (subject in each case to certain materiality standards), no material adverse effect having occurred with respect to Twilio or SendGrid, the receipt by SendGrid of a written tax opinion from Cooley LLP (legal counsel to SendGrid) and receipt by Twilio of a written tax opinion from Goodwin Procter LLP (legal counsel to Twilio) (or, if either Cooley LLP or Goodwin Procter LLP does not render such tax opinion, the applicable condition, if not waived, may be satisfied if another nationally recognized law firm proposed by Twilio or SendGrid, as applicable, and that is reasonably acceptable to SendGrid or Twilio, as applicable, renders such tax opinion).

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        We cannot be certain when, or if, the conditions to the merger will be satisfied or waived, or that the merger will be completed.

    Termination of the Merger Agreement (See page 88)

        At any time before the effective time of the merger, whether before or after Twilio's and SendGrid's respective stockholder votes, the parties may terminate the merger agreement by mutual written consent.

        At any time before the effective time of the merger, either party may terminate the merger agreement:

    if the merger does not close on or before 11:59 p.m. New York City time on July 15, 2019, which we refer to as the termination date (provided that this termination right is not available to a party whose material breach of the merger agreement is the primary cause of, or resulted in, such failure to close);

    if the SendGrid stockholder approval is not obtained (provided that this termination is not available to SendGrid if its material breach of any provision of the merger agreement is the primary cause of, or resulted in, such failure to obtain the SendGrid stockholder approval);

    if the Twilio stockholder approval is not obtained (provided that this termination right is not available to Twilio if its material breach of the merger agreement is the primary cause of, or resulted in, such failure to obtain the Twilio stockholder approval); or

    if any law or judgment permanently restraining, enjoining or otherwise prohibiting consummation of the merger shall become final and non-appealable (provided that this termination right is not available to a party whose material breach of its obligations under the merger agreement is the primary cause of such failure to close).

        At any time before the effective time of the merger, SendGrid may terminate the merger agreement if, (a) prior to the time the Twilio stockholder approval is obtained, (i) the Twilio Board effects a change in recommendation in relation to the merger or (ii) Twilio has materially breached its no solicitation, no change in recommendation or no alternative acquisition obligations set forth in the merger agreement, (b) prior to or after the time the SendGrid stockholder approval is obtained, Twilio breaches any representation, warranty, covenant or agreement made by Twilio under the merger agreement (subject to certain procedures and materiality exceptions) or (c) prior to the time the SendGrid stockholder approval is obtained, the SendGrid Board authorizes SendGrid to enter into an alternative acquisition agreement pursuant to a superior proposal and SendGrid pays to Twilio any required termination fee.

        At any time before the effective time of the merger, Twilio may terminate the merger agreement if, (a) prior to the time the SendGrid stockholder approval is obtained, (i) the SendGrid Board effects a change in recommendation in relation to the merger or (ii) SendGrid has materially breached its no solicitation, no change in recommendation or no alternative acquisition obligations set forth in the merger agreement, (b) prior to or after the time the Twilio stockholder approval is obtained, SendGrid breaches any representation, warranty, covenant or agreement made by SendGrid under the merger agreement (subject to certain procedures and materiality exceptions) or (c) prior to the time the Twilio stockholder approval is obtained, the Twilio Board authorizes Twilio to enter into an alternative acquisition agreement pursuant to a superior proposal and Twilio pays to SendGrid any required termination fee.

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    Expenses and Termination Fees (See page 89)

        SendGrid will be required to pay a termination fee of $69 million, which we refer to as the SendGrid termination fee, if the merger agreement is terminated (i) by Twilio, if the SendGrid Board changes its recommendation that the SendGrid stockholders vote in favor of the adoption of the merger agreement or (ii) by SendGrid, if the SendGrid Board authorizes SendGrid to enter into an alternative acquisition agreement with respect to a superior proposal that the SendGrid Board determines is more financially favorable to the SendGrid stockholders than the merger. SendGrid will also be required to pay the SendGrid termination fee if (i) the merger agreement is terminated by Twilio or SendGrid due to a failure to close the merger by the termination date or failure to obtain the requisite SendGrid stockholder approval, (ii) prior to such termination referred to in clause (i) of this sentence, but after the date of the merger agreement, a bona fide acquisition proposal shall have been publicly made to SendGrid or its stockholders and not publicly withdrawn, and (iii) within nine months after the date of a termination in either of the cases referred to in clause (i) of this section, SendGrid consummates an acquisition proposal with respect to a superior proposal or enters into an agreement contemplating an acquisition proposal with respect to a superior proposal that is subsequently consummated.

        Twilio will be required to pay a termination fee of $120 million, which we refer to as the Twilio termination fee, if the merger agreement is terminated in certain circumstances, including (i) by SendGrid, if the Twilio Board changes its recommendation that Twilio stockholders vote in favor of the issuance of Twilio Class A common stock in connection with the merger or (ii) by Twilio, if the Twilio Board authorizes Twilio to enter into an alternative acquisition agreement with respect to a superior proposal that the Twilio Board determines is more financially favorable to the Twilio stockholders than the merger. Twilio will also be required to pay the Twilio termination fee if (i) the merger agreement is terminated by Twilio or SendGrid due to a failure to close the merger by the termination date or failure to obtain the Twilio stockholder approval, (ii) prior to such termination referred to in clause (i) of this sentence, but after the date of the merger agreement, a bona fide acquisition proposal shall have been publicly made to Twilio or its stockholders and not publicly withdrawn, and (iii) within nine months after the date of a termination in either of the cases referred to in clause (i) of this section, Twilio consummates an acquisition proposal with respect to a superior proposal or enters into an agreement contemplating an acquisition proposal with respect to a superior proposal that is subsequently consummated.

        Further, if the merger agreement is terminated for failure to obtain the Twilio stockholder approval and any of the shares of Twilio Class B common stock subject to the irrevocable proxies described above fail to be voted in favor of the issuance of the Twilio Class A common stock in connection with the merger, Twilio will be required to pay the Twilio termination fee. Except as described in the previous sentence, in connection with the termination by either Twilio or SendGrid due to such party's failure to obtain its respective, requisite stockholder approval, such party shall reimburse the other party for all reasonable and documented out-of-pocket expenses of the other party up to $5 million as set forth in the merger agreement.

Regulatory Approvals Required for the Merger (See page 147)

        As more fully described in this joint proxy statement/prospectus, the completion of the merger is subject to the expiration or earlier termination of the waiting period (and any extension thereof) applicable to the merger under the HSR Act.

        SendGrid and Twilio received notification of early termination of the waiting period under the HSR Act on November 20, 2018.

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Accounting Treatment (See page 153)

        Twilio prepares its consolidated financial statements in accordance with accounting principles generally accepted in the United States, which we refer to as GAAP. The merger will be accounted for using the acquisition method of accounting, with Twilio treated as the acquiror. Please see the section entitled "The Merger—Accounting Treatment" on page 153 of this joint proxy statement/prospectus.

Appraisal Rights (See page 197)

        Under Delaware law, the SendGrid stockholders are not entitled to appraisal rights in connection with the merger or any other transaction contemplated by the merger agreement.

        Under Delaware law, the Twilio stockholders are not entitled to appraisal rights in connection with the issuance of shares of Twilio Class A common stock in the merger pursuant to the terms of the merger agreement.

Litigation Relating to the Merger (See page 148)

        Two putative class action lawsuits have been filed by SendGrid stockholders. The lawsuits seek to enjoin the merger, to recover damages if the merger is consummated, attorneys' fees, and other relief. Additional lawsuits arising out of the merger may be filed in the future. For a more detailed description of litigation in connection with the merger, see "The Merger—Litigation Relating to the Merger" beginning on page 148 of this joint proxy statement/prospectus.

SendGrid's Executive Officers and Directors Have Financial Interests in the Merger That Differ from the Interests of SendGrid Stockholders (See page 140)

        Certain members of the SendGrid Board and certain executive officers of SendGrid may be deemed to have financial interests in the merger that are in addition to, or different from, the interests of other SendGrid stockholders generally. The SendGrid Board (excluding director Byron Deeter, who recused himself from all deliberations due to his concurrent service as a director of Twilio) was aware of these interests and considered them, among other matters, in approving the merger and the merger agreement and in making the recommendations that SendGrid stockholders adopt the merger agreement. These potential interests include:

    Accelerated vesting of equity awards upon the effective time of the merger and upon certain terminations of employment or service following the effective time of the merger;

    Continued employment of executive officers and new compensation and benefits arrangements for certain executive officers with Twilio following the merger;

    Cash severance and other benefits upon certain terminations of employment or service following the effective time of the merger;

    Indemnification by the combined company for liabilities for acts or omissions occurring at or prior to the effective time of the merger; and

    SendGrid director Byron Deeter's concurrent service as a director of Twilio, his position as a partner of Bessemer Venture Partners and the beneficial ownership of equity interests in each of SendGrid and Twilio by funds affiliated with Bessemer Venture Partners, and, in the case of Twilio, through a trust controlled by Mr. Deeter.

        For additional details about these interests, see "Merger Agreement—Financial Interests of SendGrid Directors and Executive Officers in the Merger" beginning on page 140 of this joint proxy statement/prospectus.

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Rights of SendGrid Stockholders Will Change as a Result of the Merger (See page 185)

        As a result of the merger, SendGrid stockholders will become holders of shares of Twilio Class A common stock, and their rights will be governed by the Amended and Restated Certificate of Incorporation of Twilio and Twilio's Amended and Restated Bylaws (instead of the Amended and Restated Certificate of Incorporation of SendGrid and SendGrid's Amended and Restated Bylaws) and the General Corporation Law of Delaware, which we refer to as the DGCL. Following the merger, former SendGrid stockholders will have different rights as holders of Twilio Class A common stock than they had as SendGrid stockholders due to differences in the organizational documents of Twilio and SendGrid, including the fact that Twilio has two classes of common stock while SendGrid has only one class of common stock. SendGrid stockholders will receive Twilio Class A common stock, which has one vote per share. Twilio also has outstanding Twilio Class B common stock, which has 10 votes per share and votes together with the Twilio Class A common stock on all matters submitted to the vote of the stockholders of Twilio, except to the extent a class vote is required under applicable law or the governing documents of Twilio. After giving pro forma effect to the issuance of Twilio Class A common stock in the merger, we estimate that the holders of Twilio Class B common stock will control approximately 64.6% of the voting power of Twilio (assuming no further issuances of Twilio Class A common stock or Twilio Class B common stock, including upon conversion of Twilio's outstanding convertible securities). 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 Twilio Special Meeting

        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, at 8:00 a.m., local time, on January 30, 2019. At the Twilio special meeting, Twilio stockholders will be asked to consider and vote upon the following proposals:

    the Twilio stock issuance proposal; and

    the Twilio adjournment proposal.

        You may vote at the Twilio special meeting if you owned shares of Twilio Class A common stock and/or Twilio Class B common stock at the close of business on December 13, 2018, the Twilio record date. You may cast 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, including (i) shares held directly in your name as the stockholder of record and (ii) shares held for you as the beneficial owner in street name through a broker, bank, or other nominee. On the Twilio record date, there were outstanding a total of 80,667,248 shares of Twilio Class A common stock and 19,349,115 shares of Twilio Class B common stock entitled to vote 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 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).

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The SendGrid Special Meeting

        The SendGrid special meeting will be held at the offices of SendGrid, located at 1801 California Street, Suite 500, Denver, Colorado 80202, at 9:00 a.m., local time, on January 30, 2019. At the SendGrid special meeting, SendGrid stockholders will be asked to consider and vote upon the following proposals:

    the SendGrid merger proposal;

    the SendGrid compensation proposal; and

    the SendGrid adjournment proposal.

        You may vote at the SendGrid special meeting if you owned shares of SendGrid common stock at the close of business on December 13, 2018, the SendGrid record date. You may cast one vote for each share of SendGrid common stock that you owned as of the SendGrid record date, including (i) shares held directly in your name as the stockholder of record and (ii) shares held for you as the beneficial owner in street name through a broker, bank, or other nominee. On the SendGrid record date, there were outstanding a total of 47,659,204 shares of SendGrid common stock entitled to vote at the SendGrid special meeting.

        Completion of the merger is conditioned on the approval of the 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. 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. 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.

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SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA OF TWILIO

        The following tables set forth selected consolidated financial information for Twilio. The selected consolidated statements of operations data for the years ended December 31, 2015, 2016 and 2017 and the consolidated balance sheet data as of December 31, 2016 and 2017 are derived from Twilio's audited financial statements and related notes that are incorporated by reference into this joint proxy statement/prospectus from Twilio's Annual Report on Form 10-K for the year ended December 31, 2017. The selected consolidated statements of operations data for the years ended December 31, 2013 and 2014 and the consolidated balance sheet data as of December 31, 2013, 2014 and 2015 are derived from the audited financial statements of Twilio that are not included in or incorporated by reference into this joint proxy statement/prospectus.

        The selected historical consolidated unaudited statements of operations data for the nine months ended September 30, 2017 and 2018 and the selected historical consolidated unaudited balance sheet data as of September 30, 2018 have been derived from the unaudited condensed consolidated financial statements of Twilio, which are incorporated by reference into this joint proxy statement/prospectus. The selected historical consolidated unaudited balance sheet data as of September 30, 2017 has been derived from Twilio's unaudited condensed consolidated financial statements that have not been incorporated by reference into this joint proxy statement/prospectus.

        The following information is only a summary and should be read together with Twilio's consolidated financial statements, the notes related thereto and management's related reports on Twilio's financial condition and performance, all of which are contained in Twilio's Annual Report on Form 10-K for the year ended December 31, 2017 and in subsequent reports filed with the SEC, which are incorporated herein by reference. See "Where You Can Find More Information" on page 199 of this joint proxy statement/prospectus. The information set forth below is only a summary and it is not necessarily indicative of the results of future operations of Twilio, nor does it include the effects of the merger. Interim results for the nine months ended and as of September 30, 2018 are not necessarily indicative of, and are not projections for, the results to be expected for the fiscal year ended December 31, 2018.

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  Year Ended December 31,   Nine Months
Ended September 30,
 
 
  2013   2014   2015   2016   2017   2017   2018  
 
  (in thousands, except share and per share data)
 

Consolidated Statements of Operations Data:

                                           

Revenue

  $ 49,920   $ 88,846   $ 166,919   $ 277,335   $ 399,020   $ 283,784   $ 445,765  

Cost of Revenue(1)(2)

    25,868     41,423     74,454     120,520     182,895     127,873     204,553  

Gross profit

    24,052     47,423     92,465     156,815     216,125     155,911     241,212  

Operating expenses:

                                           

Research and development(1)(2)

    13,959     21,824     42,559     77,926     120,739     87,910     119,727  

Sales and marketing(1)(2)

    21,931     33,322     49,308     65,267     100,669     73,047     116,520  

General and administrative(1)(2)

    15,012     18,960     35,991     51,077     59,619     40,810     76,038  

Charitable contribution

                3,860     1,172         175  

Total operating expenses

    50,902     74,106     127,858     198,130     282,199     201,767     312,460  

Loss from operations

    (26,850 )   (26,683 )   (35,393 )   (41,315 )   (66,074 )   (45,856 )   (71,248 )

Other income (expenses), net

    (4 )   (62 )   11     317     3,071     1,969     (3,172 )

Loss before provision for income taxes

    (26,854 )   (26,745 )   (35,382 )   (40,998 )   (63,003 )   (43,887 )   (74,420 )

Provision for income taxes

        (13 )   (122 )   (326 )   (705 )   (902 )   (371 )

Net loss

    (26,854 )   (26,758 )   (35,504 )   (41,324 )   (63,708 )   (44,789 )   (74,791 )

Deemed dividend to investors in relation to tender offer

            (3,392 )                

Net loss attributable to common stockholders

  $ (26,854 ) $ (26,758 ) $ (38,896 ) $ (41,324 ) $ (63,708 ) $ (44,789 ) $ (74,791 )

Net loss per share attributable to common stockholders, basic and diluted

  $ (1.59 ) $ (1.58 ) $ (2.19 ) $ (0.78 ) $ (0.70 ) $ (0.49 ) $ (0.78 )

Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted

    16,916,035     16,900,124     17,746,526     53,116,675     91,224,607     90,543,087     96,359,437  

(1)
Includes stock-based compensation expense as follows:
 
  Year Ended December 31,   Nine Months
Ended
September 30,
 
 
  2013   2014   2015   2016   2017   2017   2018  
 
  (in thousands)
 

Cost of revenue

  $ 27   $ 39   $ 65   $ 291   $ 650   $ 460   $ 772  

Research and development

    810     1,577     4,046     12,946     22,808     16,687     28,500  

Sales and marketing

    753     1,335     2,389     4,972     9,822     6,961     14,154  

General and administrative

    567     1,027     2,377     6,016     16,339     11,865     17,861  

Total

  $ 2,157   $ 3,978   $ 8,877   $ 24,225   $ 49,619   $ 35,973   $ 61,287  

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(2)
Includes amortization of acquired intangibles as follows:
 
  Year Ended December 31,   Nine Months
Ended
September 30,
 
 
  2013   2014   2015   2016   2017   2017   2018  
 
  (in thousands)
 

Cost of revenue

  $   $   $ 239   $ 619   $ 4,644   $ 3,429   $ 3,719  

Research and development

            130     151     139     101     22  

Sales and marketing

                    753     539     816  

General and administrative

            95     110     84     64     60  

Total

  $   $   $ 464   $ 880   $ 5,620   $ 4,133   $ 4,617  


 
  As of December 31,   As of September 30,  
 
  2013   2014   2015   2016   2017   2017   2018  
 
  (in thousands)
 

Consolidated Balance Sheet Data:

                                           

Cash and cash equivalents

  $ 54,715   $ 32,627   $ 108,835   $ 305,665   $ 115,286   $ 91,906   $ 469,132  

Marketable securities

                    175,587     192,031     276,221  

Working capital

    48,403     23,151     96,032     279,676     274,738     271,616     725,322  

Property and equipment, net

    3,688     6,751     14,058     37,552     50,541     47,718     59,205  

Total assets

    66,707     54,974     157,516     412,694     449,782     443,548     1,003,797  

Total stockholders' equity

  $ 52,900   $ 31,194   $ 116,625     329,447   $ 359,846   $ 355,000   $ 434,353  

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SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA OF SENDGRID

        The following tables present SendGrid's selected historical consolidated financial data. The selected historical consolidated statements of operations data for the years ended December 31, 2015, 2016 and 2017 and the selected historical consolidated balance sheet data as of December 31, 2016 and 2017 have been derived from the audited consolidated financial statements of SendGrid contained in its Annual Report on Form 10-K for the year ended December 31, 2017, which is incorporated by reference into this joint proxy statement/prospectus. The selected historical consolidated statement of operations data for the year ended December 31, 2014 and the selected historical consolidated balance sheet data as of December 31, 2015 have been derived from SendGrid's audited consolidated financial statements that have not been incorporated by reference into this joint proxy statement/prospectus.

        The selected historical consolidated unaudited statements of operations data for the nine months ended September 30, 2017 and 2018 and the selected historical consolidated unaudited balance sheet data as of September 30, 2018 have been derived from the unaudited condensed consolidated financial statements of SendGrid, which are incorporated by reference into this joint proxy statement/prospectus. The selected historical consolidated unaudited balance sheet data as of September 30, 2017 has been derived from SendGrid's unaudited consolidated financial statements that have not been incorporated by reference into this joint proxy statement/prospectus.

        The following information is only a summary and is not necessarily indicative of the results of future operations of SendGrid. You should read this selected historical consolidated financial data together with SendGrid's financial statements that are incorporated by reference into this joint proxy statement/prospectus and their accompanying notes and management's discussion and analysis of financial condition and results of operations contained therein.

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  For the Year Ended December 31,   For the Nine Months
Ended September 30,
 
 
  2014   2015   2016   2017   2017   2018  
 
  (in thousands, except per share amounts)
 

Consolidated Statements of Operations Data:

                                     

Revenue

  $ 42,776   $ 58,476   $ 79,929   $ 111,888   $ 80,159   $ 105,443  

Cost of revenue(1)(2)

    15,187     18,961     21,605     29,507     21,357     26,271  

Gross profit

    27,589     39,515     58,324     82,381     58,802     79,172  

Operating expenses:(1)(2)

                                     

Research and development

    15,290     18,959     21,178     29,643     21,208     29,854  

Selling and marketing(3)

    15,260     13,737     21,800     28,185     20,582     26,255  

General and administrative(4)(5)

    9,550     12,477     18,920     30,101     21,222     28,637  

Loss on disposal of assets

    63     1     27     22     2     84  

Total operating expenses

    40,163     45,174     61,925     87,951     63,014     84,830  

Loss from operations

    (12,574 )   (5,659 )   (3,601 )   (5,570 )   (4,212 )   (5,658 )

Other income (expense), net(6)

    (386 )   (195 )   (307 )   (683 )   (515 )   1,652  

Net loss before provision for income taxes

    (12,960 )   (5,854 )   (3,908 )   (6,253 )   (4,727 )   (4,006 )

Provision for income taxes

                         

Net loss

  $ (12,960 ) $ (5,854 ) $ (3,908 ) $ (6,253 ) $ (4,727 ) $ (4,006 )

Weighted average shares used in computing net loss per share, basic and diluted

    5,194     7,091     7,521     8,499     7,938     43,841  

Net loss per share, basic and diluted

  $ (2.50 ) $ (0.83 ) $ (0.52 ) $ (0.74 ) $ (0.60 ) $ (0.09 )

(1)
Amounts include stock-based compensation expense as follows:
 
  For the Year Ended December 31,   For the Nine
Months Ended
September 30,
 
 
  2014   2015   2016   2017   2017   2018  

Cost of revenue

  $ 103   $ 97   $ 131   $ 474   $ 337   $ 897  

Research and development

    157     379     552     1,294     749     3,016  

Selling and marketing

    125     193     402     899     596     1,165  

General and administrative

    309     706     814     2,313     995     3,004  

Total stock-based compensation

  $ 694   $ 1,375   $ 1,899   $ 4,980   $ 2,677   $ 8,082  

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(2)
Amounts include merger and acquisition expense as follows:
 
  For the Year Ended December 31,   For the Nine
Months Ended
September 30,
 
 
  2014   2015   2016   2017   2017   2018  

Cost of revenue

  $   $   $   $ 67   $ 47   $ 60  

Research and development

                545     342     410  

Selling and marketing

                16     11     14  

General and administrative

                266     261     1,392  

Total merger and acquisition expense

  $   $   $   $ 894   $ 661   $ 1,876  
(3)
Includes non-capitalizable costs related to preparation to become and operate as a public company of $0.2 million for the year ended December 31, 2017. There were no such IPO preparation costs included in selling and marketing expense during any of the periods presented.

(4)
Includes non-capitalizable costs related to preparation to become and operate as a public company of zero, zero, $0.1 million, $1.7 million, $1.0 million, and zero for the years ended December 31, 2014, 2015, 2016, and 2017, and the nine months ended September 30, 2017 and 2018.

(5)
Includes restructuring expense of zero, zero, $0.4 million, $1.2 million, $1.1 million, and $0.7 million for the years ended December 31, 2014, 2015, 2016, and 2017, and the nine months ended September 30, 2017 and 2018, respectively.

(6)
Includes warrant fair value adjustment of $0.1 million, zero, $0.1 million, $0.7 million, $0.4 million, and zero for the years ended December 31, 2014, 2015, 2016, and 2017, and the nine months ended September 30, 2017 and 2018, respectively.
 
  As of December 31,   As of September 30,  
 
  2015   2016   2017   2017   2018  
 
  (in thousands)
 

Consolidated Balance Sheet Data:

                               

Cash and cash equivalents

  $ 9,269   $ 40,400   $ 175,496   $ 37,397   $ 186,423  

Working capital

  $ 5,665   $ 33,775   $ 168,498   $ 29,955   $ 175,892  

Property and equipment, net

  $ 10,413   $ 19,190   $ 29,192   $ 26,322   $ 35,858  

Total assets

  $ 24,676   $ 66,635   $ 223,283   $ 79,748   $ 245,112  

Total stockholders' equity (deficit)

  $ (35,947 ) $ (37,780 ) $ 179,774   $ (38,999 ) $ 196,850  

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SELECTED UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL DATA

        The following selected unaudited pro forma condensed combined financial data was prepared using the acquisition method of accounting with Twilio as the accounting acquiror. The selected unaudited pro forma condensed combined balance sheet data assumes the merger of Twilio and SendGrid took place on September 30, 2018. The selected unaudited pro forma condensed combined statements of operations data assumes the merger of Twilio and SendGrid took place on January 1, 2017.

        The following selected unaudited pro forma condensed combined financial data is for illustrative purposes only and is not necessarily indicative of the combined financial position or results of operations of future periods or the results that actually would have been realized had the entities been a single entity during these periods. Future results may vary significantly from the results reflected because of various factors, including those discussed in the Section entitled "Risk Factors." The following selected unaudited pro forma condensed combined financial data should be read in conjunction with the section entitled "Unaudited Pro Forma Condensed Combined Financial Statements" and related notes included in this joint proxy statement/prospectus.

Selected Unaudited Pro Forma Condensed Combined Statements
of Operations Data (in thousands except per share amounts):
  Nine Months Ended
September 30,
2018
  Year Ended
December 31,
2017
 

Revenue

  $ 551,208   $ 510,908  

Loss from operations

    (182,067 )   (220,258 )

Loss before (provision) benefit for income taxes

    (183,587 )   (217,870 )

Net loss attributable to common stockholders

    (160,707 )   (170,617 )

Net loss per share attributable to common stockholders:

   
 
   
 
 

Basic

 
$

(1.35

)

$

(1.49

)

Diluted

  $ (1.35 ) $ (1.49 )

 

Selected Unaudited Pro Forma Condensed Combined
Balance Sheet Data (in thousands):
  As of
September 30,
2018
 

Total assets

  $ 3,236,273  

Total liabilities

    742,388  

Total stockholders' equity

  $ 2,493,885  


COMPARATIVE HISTORICAL AND UNAUDITED PRO FORMA PER SHARE DATA

        The following tables for the year ended December 31, 2017 and the nine months ended September 30, 2018 summarize selected per share data for (i) Twilio and SendGrid on an audited historical basis, (ii) Twilio on an unaudited pro forma combined basis giving effect to the merger using the acquisition method of accounting and (iii) SendGrid on an unaudited pro forma equivalent basis based on the exchange ratio of 0.485 of a share of Twilio Class A common stock per share for SendGrid common stock.

        The information in the table related to Twilio and SendGrid is derived from Twilio's and SendGrid's respective historical consolidated financial statements incorporated by reference herein, as well as the unaudited pro forma condensed combined financial statements and accompanying notes included elsewhere in this joint proxy statement/prospectus.

        The unaudited pro forma per share data below is presented for illustrative purposes only. The pro forma adjustments to the statement of operations data are based on the assumption that the merger

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was completed on January 1, 2017, and the pro forma adjustments to the balance sheet data are based on the assumption that the merger was completed on September 30, 2018.

        Either company's actual historical financial condition and results of operations may have been different had the companies always been combined. You should not rely on this information as being indicative of the historical financial condition and results of operations that would have actually been achieved or of the future results of Twilio after the completion of the merger.

        You should read the information below together with the historical consolidated financial statements and related notes of Twilio and SendGrid as of and for the applicable periods, which have been incorporated by reference into this joint proxy statement/prospectus, along with the information under the heading "Unaudited Pro Forma Condensed Combined Financial Statements" and related notes included in this joint proxy statement/prospectus.

 
  Twilio Common Stock   SendGrid Common Stock  
 
  Historical   Pro Forma
Combined
  Historical   Pro Forma
Equivalent(1)
 

Net loss per share attributable to common stockholders

                         

Basic and Diluted

                         

Year Ended December 31, 2017

  $ (0.70 ) $ (1.49 ) $ (0.74 ) $ (0.72 )

Nine Months Ended September 30, 2018          

  $ (0.78 ) $ (1.35 ) $ (0.09 ) $ (0.65 )

Book Value per Share

                         

Year Ended December 31, 2017

  $ 3.83     N/A   $ 4.26     N/A  

Nine Months Ended September 30, 2018          

  $ 4.40   $ 20.49   $ 4.18   $ 9.94  

(1)
Calculated by multiplying the "Pro Forma Combined" amounts by the exchange ratio of 0.485

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COMPARATIVE STOCK PRICE DATA AND DIVIDENDS

        Twilio Class A common stock and SendGrid common stock are both traded on the NYSE under the symbols "TWLO" and "SEND", respectively. The following table presents the high and low price per share of Twilio Class A common stock and SendGrid common stock on October 15, 2018, the last full trading day before public announcement that Twilio and SendGrid had entered into the merger agreement, and December 13, 2018, the last practicable trading day before the date of this joint proxy statement/prospectus.

 
  Twilio Class A
Common Stock
  SendGrid
Common Stock
 
Date
  High   Low   Close   High   Low   Close  

October 15, 2018

    77.14     73.00     76.13     31.285     29.710     30.930  

December 13, 2018

    98.90     93.02     95.97     47.630     44.830     46.250  

        For illustrative purposes, the following table provides equivalent high and low price per share of SendGrid common stock on each of the specified dates. These equivalent high and low price per share amounts reflect the fluctuating value of Twilio Class A common stock that SendGrid stockholders would receive in exchange for each share of SendGrid common stock if the merger were completed on either of these dates and are calculated by multiplying the high and low price per share of Twilio Class A common stock by the exchange ratio of 0.485.

 
  Twilio Class A
Common Stock
  SendGrid Equivalent
Per Share
 
Date
  High   Low   Close   High   Low   Close  

October 15, 2018

    77.14     73.00     76.13     37.413     35.405     36.923  

December 13, 2018

    98.90     93.02     95.97     47.967     45.115     46.545  

        The market value of the shares of Twilio Class A common stock to be issued in exchange of shares of SendGrid common stock upon the completion of the merger will not be known at the time of the Twilio and SendGrid special meetings. The above tables show only historical comparisons. Because the market prices of Twilio Class A common stock and SendGrid common stock will likely fluctuate prior to the merger, these comparisons may not provide meaningful information to (i) Twilio stockholders in determining whether to approve the issuance of shares of Twilio Class A common stock to holders of SendGrid common stock in connection with the merger pursuant to the merger agreement or (ii) SendGrid stockholders in determining whether to adopt the merger agreement. Twilio stockholders and SendGrid stockholders are encouraged to obtain current market quotations for shares of Twilio Class A common stock and SendGrid common stock and to review carefully the other information contained in this joint proxy statement/prospectus or incorporated by reference in this joint proxy statement/prospectus in considering whether to approve the issuance of shares of Twilio Class A common stock in connection with the merger pursuant to the terms of the merger agreement, in the case of Twilio stockholders, and whether to adopt the merger agreement, in the case of SendGrid stockholders. See the section entitled "Where You Can Find More Information" beginning on page 199 of this joint proxy statement/prospectus.

Holders

        As of 5:00 p.m. U.S. Eastern Time on December 13, 2018, the record date for the Twilio special meeting, 80,667,248 shares of Twilio Class A common stock, held by 40 holders of record, and 19,349,115 shares of Twilio Class B common stock, held by 47 holders of record, were outstanding and entitled to vote at the Twilio special meeting. As of 5:00 p.m. U.S. Eastern Time on December 13, 2018, the record date for the SendGrid special meeting, 47,659,204 shares of SendGrid common stock, held by 64 holders of record, were outstanding and entitled to vote at the SendGrid special meeting.

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RISK FACTORS

        In addition to the other information included and incorporated by reference into this joint proxy statement/prospectus, including the matters addressed in the section entitled "Cautionary Statement Regarding Forward-Looking Statements," you should carefully consider the following risks before deciding whether to vote for the adoption and approval of the merger agreement, in the case of SendGrid stockholders, or for the issuance of shares of Twilio Class A common stock in connection with the merger, in the case of Twilio stockholders. In addition, you should read and consider the risks associated with each of the businesses of Twilio and SendGrid because these risks will also affect the combined company. These risks can be found in Twilio's and SendGrid's respective Quarterly Reports on Form 10-Q for the fiscal quarter ended September 30, 2018, both of which are filed with the SEC and incorporated by reference into this joint proxy statement/prospectus. You should also read and consider the other information in this joint proxy statement/prospectus and the other documents incorporated by reference into this joint proxy statement/prospectus. See the section entitled "Where You Can Find More Information," beginning on page 199 of this joint proxy statement/prospectus.

Risk Factors Relating to the Merger

         The merger may not be completed on the terms or timeline currently contemplated, or at all.

        The consummation of the merger is subject to numerous conditions, including (1) the expiration or termination of any applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, or the HSR Act, (2) the effectiveness of the Registration Statement on Form S-4 of which this joint proxy statement/prospectus forms a part, (3) the approval by the SendGrid stockholders of the SendGrid merger proposal, (4) the approval by the Twilio stockholders of the Twilio stock issuance proposal, (5) the receipt by Twilio, on the one hand, and SendGrid, on the other hand, of a written tax opinion from their respective counsel (or if such counsel does not render such tax opinion, another nationally recognized law firm proposed by SendGrid or Twilio, as applicable, and that is reasonably acceptable to Twilio or SendGrid, as applicable) to the effect that the merger will be treated as a "reorganization" for U.S. federal income tax purposes and (6) other customary closing conditions. See the section "The Merger Agreement—Conditions to Completion of the Merger."

        If the merger is not completed for any reason, including the failure to complete the merger by July 15, 2019 (or such later date to which such date may be extended in accordance with the terms of the merger agreement), the price of Twilio Class A common stock and/or the price of the SendGrid common stock may decline to the extent that the market price of Twilio Class A common stock or SendGrid common stock, as applicable, reflects or previously reflected positive market assumptions that the merger would be completed and the related benefits would be realized. In addition, Twilio and SendGrid have expended and will continue to expend significant management time and resources and have incurred and will continue to incur significant expenses due to legal, advisory, printing and financial services fees related to the merger. These expenses must be paid regardless of whether the merger is consummated. If the merger is not consummated because the merger agreement is terminated, Twilio may be required under certain circumstances to pay SendGrid a termination fee of $120 million or SendGrid may be required under certain circumstances to pay Twilio a termination fee of $69 million. There is no assurance that the merger will be consummated. See "The Merger Agreement" beginning on page 68 of this joint proxy statement/prospectus.

         The exchange ratio is fixed and will not be adjusted in the event of any change in either Twilio's or SendGrid's stock price.

        Upon the closing of the merger, each share of SendGrid common stock will be converted into the right to receive 0.485, which we refer to as the exchange ratio, of a share of Twilio Class A common stock. The exchange ratio was fixed in the merger agreement and will not be adjusted for changes in the market price of either Twilio Class A common stock or SendGrid common stock. Changes in the

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price of Twilio Class A common stock prior to the merger will affect the market value of the merger consideration that SendGrid stockholders will receive on the date of the merger. Stock price changes may result from a variety of factors (many of which are beyond Twilio's and SendGrid's control), including the following factors:

    changes in Twilio's and SendGrid's respective businesses, operations, financial position or prospects;

    changes in market assessments of the business, operations, financial position or prospects of either company or the combined company;

    market assessments of the likelihood that the merger will be completed, including related considerations regarding regulatory approvals of the merger;

    interest rates, general market, political and economic conditions and other factors generally affecting the price of Twilio's Class A common stock or SendGrid's common stock; and

    federal, state and local legislation, governmental regulation and legal developments affecting the businesses of SendGrid or Twilio.

        Under the merger agreement, there will be no adjustment to the exchange ratio for changes in the market price of either shares of Twilio Class A common stock or shares of SendGrid common stock, and neither company is permitted to terminate the merger agreement or resolicit the vote of Twilio stockholders or SendGrid stockholders solely because of changes in the market prices of either company's stock. We encourage you to obtain current market quotations for shares of Twilio Class A common stock and for shares of SendGrid common stock before voting.

        Because the merger will be completed after the date of the special meetings, at the time of your special meeting, you will not know the exact market value of the Twilio Class A common stock that SendGrid stockholders will receive upon completion of the merger. Accordingly, you should consider the following:

    If the price of Twilio Class A common stock increases between the date the merger agreement was signed or the date of the Twilio special meeting and the effective time of the merger, SendGrid stockholders will receive shares of Twilio Class A common stock that have a market value upon completion of the merger that is greater than the market value of such shares calculated pursuant to the exchange ratio when the merger agreement was signed or the date of the Twilio special meeting, respectively. Therefore, while the number of shares of Twilio Class A common stock to be issued per SendGrid common share is fixed, Twilio stockholders cannot be sure that the market value of the consideration that will be paid to SendGrid stockholders upon completion of the merger will not increase.

    If the price of Twilio Class A common stock declines between the date the merger agreement was signed or the date of the SendGrid special meeting and the effective time of the merger, SendGrid stockholders will receive shares of Twilio Class A common stock that have a market value upon completion of the merger that is less than the market value of such shares calculated pursuant to the exchange ratio on the date the merger agreement was signed or the date of the SendGrid special meeting, respectively. Therefore, while the number of Twilio Class A common shares to be issued per share of SendGrid common stock is fixed, SendGrid stockholders cannot be sure that the market value of the Twilio Class A common stock they will receive upon completion of the merger will not decrease.

         Required regulatory approvals may not be received, may take longer than expected to be received or may impose conditions that are not presently anticipated or cannot be met.

        Completion of the merger is conditioned upon the expiration or termination of the waiting period applicable to the merger under the HSR Act (for which SendGrid and Twilio received notification of

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early termination of the waiting period under the HSR Act on November 20, 2018). Even though Twilio and SendGrid received notification of early termination of the waiting period under the HSR Act, at any time before or after the merger, if the U.S. Federal Trade Commission, which we refer to as the FTC, or the Antitrust Division of the Department of Justice, which we refer to as the DOJ, believes that the merger would violate the U.S. federal antitrust laws by substantially lessening competition in any line of commerce affecting U.S. consumers, the FTC or DOJ has the authority to challenge the transaction by seeking a federal court order enjoining the transaction or, if the merger has been consummated, requiring unwinding of the merger, or the divestiture of assets of Twilio, SendGrid or any of their respective subsidiaries or affiliates. U.S. state attorneys general and private persons may also bring legal action under the U.S. federal or state antitrust laws. While Twilio and SendGrid believe that the consummation of the merger will not violate any U.S. federal antitrust law, there can be no assurance that a challenge to the merger on antitrust grounds will not be made or, if a challenge is made, what the result will be.

        See "The Merger—Regulatory Approvals Required for the Merger" and "The Merger Agreement—Conditions to Completion of the Merger" beginning on pages 147 and 85 of this joint proxy statement/prospectus.

         Litigation filed or that may be filed against SendGrid, Twilio, Merger Sub and/or the members of the SendGrid Board or the Twilio Board could prevent or delay the consummation of the merger.

        Two putative class action lawsuits have been filed by SendGrid stockholders. The lawsuits seek to enjoin the merger, to recover damages if the merger is consummated, attorneys' fees and other relief. Additional lawsuits arising out of the merger may be filed in the future. For a more detailed description of litigation in connection with the merger, see "The Merger—Litigation Relating to the Merger" beginning on page 148 of this joint proxy statement/prospectus. Additional lawsuits may be filed.

        The outcome of these lawsuits or any other lawsuit that may be filed challenging the merger is uncertain. One of the conditions to the closing of the merger is that no governmental authority has issued or entered any order having the effect of enjoining or otherwise prohibiting the consummation of the merger. Accordingly, if these lawsuits or any future lawsuit is successful in obtaining an order enjoining the merger, then the merger may not be consummated within the expected time frame, or at all, and could result in substantial costs, including but not limited to, costs associated with the indemnification of directors and officers.

         Failure to complete the merger could negatively affect the stock prices and the future business and financial results of Twilio and SendGrid.

        If the merger is not completed, the ongoing businesses of SendGrid or Twilio may be adversely affected and Twilio and SendGrid will be subject to several risks, including the following:

    the possibility that SendGrid could be required to pay Twilio a termination fee of $69 million, plus reimbursement of expenses up to $5 million, if the merger is terminated under qualifying circumstances, as described under "The Merger Agreement—Termination Fees and Expenses; Liability for Breach";

    the possibility that Twilio could be required to pay SendGrid a termination fee of $120 million, plus reimbursement of expenses up to $5 million, if the merger is terminated under qualifying circumstances, as described under "The Merger Agreement—Termination Fees and Expenses; Liability for Breach";

    the incurrence of costs and expenses relating to the proposed merger, such as financing, legal, accounting, financial advisor, filing, printing and mailing fees and expenses, including the potential expense reimbursement obligations described above;

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    the possibility of a change in the trading price of Twilio Class A common stock or SendGrid common stock to the extent current trading prices reflect a market assumption that the merger will be completed;

    the possibility that Twilio or SendGrid could suffer potential negative reactions from their respective employees, customers and vendors; and

    the possibility that Twilio or SendGrid could suffer adverse consequences associated with their respective management's focus on the merger instead of on pursuing other opportunities that could have been beneficial to each company, in each case, without realizing any of the benefits contemplated by the merger.

        In addition, if the merger is not completed, Twilio or SendGrid could be subject to litigation related to any failure to complete the merger or to perform their respective obligations under the merger agreement.

        If the merger is not completed, Twilio and SendGrid cannot assure their stockholders that these risks will not materialize and will not materially affect the business, financial results and stock prices of Twilio or SendGrid.

         SendGrid stockholders and Twilio stockholders will not be entitled to appraisal rights in the merger.

        Appraisal rights are statutory rights that, if applicable under law, enable stockholders to dissent from an extraordinary transaction, such as a merger, and to demand that the corporation pay the fair value for their shares as determined by a court in a judicial proceeding instead of receiving the consideration offered to stockholders in connection with the extraordinary transaction.

        Under the DGCL § 262(b), stockholders do not have appraisal rights if the shares of stock they hold, as of the record date for determination of stockholders entitled to vote at the meeting of stockholders to act upon a merger, are either (i) listed on a national securities exchange or (ii) held of record by more than 2,000 holders. Notwithstanding the foregoing, appraisal rights are available if stockholders are required by the terms of the merger agreement to accept for their shares anything other than (a) shares of stock of the surviving corporation, (b) shares of stock of another corporation that will either be listed on a national securities exchange or held of record by more than 2,000 holders, (c) cash instead of fractional shares or (d) any combination of clauses (a) through (c).

        Twilio stockholders will not be entitled to appraisal rights in the merger with respect to their shares of Twilio Class A common stock and/or Twilio Class B common stock. Shares of SendGrid common stock are listed on the NYSE and are expected to continue to be so listed on the record date for the SendGrid special meeting. Because holders of shares of SendGrid common stock will receive shares of Twilio Class A common stock in the merger and cash in lieu of fractional shares, holders of shares of SendGrid common stock will also not be entitled to appraisal rights in the merger with respect to their shares of SendGrid common stock.

         The merger agreement contains provisions that could discourage a potential competing acquiror of either SendGrid or Twilio or could result in any competing proposal being at a lower price than it might otherwise be.

        The merger agreement contains "no-shop" provisions that, subject to limited exceptions, restrict SendGrid and Twilio's ability to solicit, encourage, facilitate or discuss competing third-party proposals to acquire all or a significant part of SendGrid or Twilio. In addition, the other party generally has an opportunity to offer to modify the terms of the proposed merger in response to any competing acquisition proposals that may be made before such board of directors may withdraw or qualify its recommendation regarding the proposals described herein. In specified circumstances, one of the parties may be required to pay a termination fee or expenses to the other party due to the termination of the merger agreement. See "The Merger Agreement—No Solicitation of Alternative Proposals," "The

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Merger Agreement—Termination of the Merger Agreement" and "The Merger Agreement—Termination Fees and Expenses; Liability for Breach" beginning on pages 77, 88 and 89 of this joint proxy statement/prospectus.

        These provisions could discourage a potential competing acquiror that might have an interest in acquiring all or a significant part of SendGrid or Twilio from considering or proposing that acquisition, even if it were prepared to pay consideration with a higher value than that market value proposed to be received or realized in the merger, or might result in a potential competing acquiror proposing to pay a lower price than it might otherwise have proposed to pay because of the added expense of the termination fee or expenses that may become payable in certain circumstances.

        If the merger agreement is terminated and either Twilio or SendGrid attempts to seek another business merger, Twilio or SendGrid, as applicable, may not be able to negotiate a transaction with another party on terms comparable or better than the terms of the merger.

         The pendency of the merger could adversely affect the business and operations of Twilio and SendGrid.

        In connection with the merger, some customers or vendors of each of Twilio and SendGrid may delay or defer decisions or reduce their level of business with either or both of the companies, any of which could negatively affect the revenues, earnings, cash flows and expenses of Twilio and SendGrid, regardless of whether the merger is completed. Similarly, while reductions in force are not planned, current and prospective employees of Twilio and SendGrid may nevertheless experience uncertainty about their future roles with the combined company following the merger, which may materially adversely affect the ability of each of Twilio and SendGrid to attract and retain key management, sales, marketing, operational and technical personnel during the pendency of the merger. In addition, due to operating covenants in the merger agreement, each of Twilio and SendGrid may be unable, during the pendency of the merger, to pursue strategic transactions, undertake significant capital projects, undertake certain significant financing transactions and otherwise pursue other actions that are not in the ordinary course of business, even if such actions would prove beneficial. Any of these effects could adversely affect the ability to generate revenue at anticipated levels prior to the completion of the merger. Moreover, the pursuit of the merger and the preparation for the integration of the companies may place a significant burden on the management and personnel of both companies. The diversion of management's attention away from operating the companies in the ordinary course could adversely affect Twilio's and SendGrid financial results.

         Current Twilio stockholders will have a reduced ownership and voting power in the combined company after the merger.

        Twilio expects to issue or reserve for issuance approximately 28,579,902 shares of Twilio Class A common stock to SendGrid equityholders in connection with the merger (including shares of Twilio Class A common stock to be issued in connection with outstanding SendGrid equity awards). Based on the number of shares of Class A common stock and Class B common stock of Twilio and common stock of SendGrid outstanding on December 13, 2018, the record date for the two companies' special meetings of stockholders, and assuming no further issuances of SendGrid common stock or Twilio Class A common stock or Twilio Class B common stock, including upon conversion of Twilio's convertible securities, upon the completion of the merger, current Twilio stockholders and former SendGrid stockholders are expected to own approximately 92.2% and 7.8% of the total voting power of Twilio, respectively.

        Twilio stockholders and SendGrid stockholders currently have the right to vote for their respective directors and on certain other matters affecting their company. If and when the merger occurs, each Twilio stockholder will remain a stockholder of Twilio with a percentage ownership of Twilio that will be smaller than the stockholder's percentage of Twilio prior to the merger (without considering such stockholder's current ownership of SendGrid common stock, if any). Correspondingly, each SendGrid

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stockholder who receives shares of Twilio Class A common stock will become a holder of Twilio Class A common stock with a percentage ownership of Twilio that will be smaller than the stockholder's percentage ownership of SendGrid (without considering such stockholder's current ownership of Twilio Class A common stock and/or Twilio Class B common stock). Each SendGrid stockholder's voting power as a percentage of the total voting power will be further reduced because Twilio has two classes of common stock and the holders of Twilio Class B common stock have 10 votes per share and vote together with the Twilio Class A common stock, which have one vote per share, on the election of the directors and other matters submitted to the stockholders for a vote. As a result, Twilio stockholders will have less voting power in Twilio than they currently have, and former SendGrid stockholders will have less voting power in Twilio than they now have with respect to SendGrid. Each of Twilio and SendGrid's pre-merger stockholders respectively, as a group, will be able to exercise less influence over the management and policies of the combined company following the consummation of the merger than immediately prior to the consummation of the merger.

         The shares of Twilio Class A common stock to be received by SendGrid stockholders upon completion of the merger will have different rights from SendGrid common stock.

        Upon completion of the merger, SendGrid stockholders will no longer be stockholders of SendGrid, but will instead become stockholders of Twilio, and their rights as Twilio stockholders will be governed by the terms of Twilio's amended and restated certificate of incorporation, as it may be amended from time to time, which we refer to as the Twilio charter, and Twilio's amended and restated bylaws, as they may be amended from time to time, which we refer to as the Twilio bylaws. The terms of the Twilio charter and Twilio bylaws are in some respects materially different from the terms of SendGrid's amended and restated certificate of incorporation, as it may be amended from time to time, which we refer to as the SendGrid charter, and SendGrid's amended and restated bylaws, as they may be amended from time to time, which we refer to as the SendGrid bylaws, which currently govern the rights of SendGrid stockholders. Additionally, SendGrid stockholders will receive Twilio Class A common stock, which has one vote per share. Twilio also has outstanding Twilio Class B common stock, which has 10 votes per share and votes together with Twilio Class A common stock on all matters submitted to the vote of the stockholders of Twilio, except to the extent a class vote is required under applicable law or under the Twilio charter documents. After giving pro forma effect to the issuance of Twilio Class A common stock in the merger, we estimate that the holders of Twilio Class B common stock will control approximately 64.6% of the voting power of Twilio (assuming no further issuances of Twilio Class A common stock or Twilio Class B common stock, including upon conversion of Twilio's outstanding convertible securities). See "Comparison of Rights of Twilio Stockholders and SendGrid Stockholders" beginning on page 185 of this joint proxy statement/prospectus for a discussion of the different rights associated with shares of Twilio Class A common stock and shares of SendGrid common stock.

         The market price of shares of Twilio Class A common stock may be affected by factors different from those that historically have affected shares of SendGrid common stock and will continue to fluctuate after the merger.

        Upon completion of the merger, holders of SendGrid common stock will become holders of Twilio Class A common stock. The businesses of Twilio differ from those of SendGrid in certain respects, and, accordingly, the financial position or results of operations and/or cash flows of Twilio after the merger, as well as the market price of shares of Twilio Class A common stock, may be affected by factors different from those currently affecting the financial position or results of operations and/or cash flows of SendGrid. In addition, the stock market has experienced significant price and volume fluctuations in recent times which, if they continue to occur, could have a material adverse effect on the market for, or liquidity of, the Twilio Class A common stock, regardless of Twilio's actual operating performance. As a result, the market price of shares of Twilio Class A common stock may fluctuate significantly

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following completion of the merger, and holders of SendGrid common stock could lose some or all of the value of their investment in Twilio Class A common stock.

         Directors and executive officers of Twilio and SendGrid have financial interests in the merger that may be different from, or in addition to, those of other Twilio stockholders and SendGrid stockholders, which could have influenced their decisions to support or approve the merger.

        In considering whether to approve the proposals at the special meetings, Twilio and SendGrid stockholders should recognize that directors and executive officers of Twilio and SendGrid have interests in the merger that may differ from, or that are in addition to, their interests as stockholders of Twilio and stockholders of SendGrid. The Twilio Board and the SendGrid Board were aware of these interests at the time each approved the merger agreement. These interests may cause Twilio's and SendGrid's directors and executive officers to view the merger differently than you may view it as a stockholder. See "The Merger—Financial Interests of Twilio Directors and Executive Officers in the Merger" and "The Merger—Financial Interests of SendGrid Directors and Executive Officers in the Merger" beginning on pages 139 and 140 of this joint proxy statement/prospectus.

         The opinions obtained by the Twilio Board and SendGrid Board from their respective financial advisors do not and will not reflect changes in circumstances after the date of such opinions.

        The Twilio Board received a written opinion dated October 15, 2018 from Goldman Sachs & Co. LLC, its financial advisor, that the merger consideration to be paid by Twilio was fair, from a financial point of view, to Twilio, as of such date, and based on and subject to the qualifications, limitations and assumptions set forth in such opinion. The SendGrid Board received a written opinion dated October 15, 2018 from Morgan Stanley & Co. LLC, its financial advisor, that as of such date and based upon and subject to the assumptions made, procedures followed, matters considered and qualifications and limitations on the scope of review undertaken by Morgan Stanley as set forth in its opinion, the exchange ratio pursuant to the merger agreement was fair from a financial point of view to the holders of shares of SendGrid common stock (other than the Excluded Shares). Changes in the operations or prospects of Twilio or SendGrid, general market and economic conditions and other factors that may be beyond the control of Twilio and SendGrid, and on which the above-described opinions were based, may alter the value of Twilio or SendGrid or the prices of shares of Twilio Class A common stock or SendGrid common stock by the time the merger is completed. Twilio and SendGrid have not obtained, and do not expect to request, updated opinions from their respective financial advisors. None of the above-listed opinions speak to any date other than the date of such opinion. For a more complete description of the above-described opinions, please refer to "The Merger—Opinion of Twilio's Financial Advisor, Goldman Sachs & Co. LLC" and "The Merger—Opinion of SendGrid's Financial Advisor, Morgan Stanley & Co. LLC."

         Due to the merger, the ability of Twilio to use SendGrid's net operating losses to offset future taxable income may be restricted and these net operating losses could expire or otherwise be unavailable.

        As of December 31, 2017, SendGrid had federal net operating loss carryforwards, which we refer to as NOLs, of approximately $37.1 million. In general, under Section 382 of the Code, a corporation that undergoes an "ownership change" is subject to limitations on its ability to utilize its pre-ownership change NOLs to offset future taxable income. As of December 31, 2017, SendGrid has not completed a Section 382 limitation study, and postponed completion of its prior study, due to a significant level of legacy ownership both before and after its initial public offering. If the merger is completed, SendGrid's existing NOLs may be subject to limitations and Twilio may not be able to fully use NOLs generated prior to 2018 to offset future taxable income. In addition, if Twilio undergoes any subsequent ownership change, its ability to utilize NOLs would be limited.

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         If the merger does not qualify as a "reorganization" for U.S. federal income tax purposes, U.S. holders will be required to recognize gain or loss for U.S. federal income tax purposes at the time of the exchange of their SendGrid common stock for the merger consideration in the merger.

        The U.S. federal income tax consequences of the merger to U.S. holders (as defined under the heading "Material U.S. Federal Income Tax Consequences") will depend on whether the merger qualifies as a "reorganization" for U.S. federal income tax purposes.

        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.

        There can be no assurance, that the Internal Revenue Service, which we refer to as the IRS, will not take a contrary position to views expressed herein or that a court will not agree with a contrary position of the IRS. If, contrary to the opinion from counsel, the merger fails to qualify as a reorganization or if any requirement for the merger to qualify as a "reorganization" within the meaning of Section 368(a) of the Code is not satisfied, a U.S. holder of SendGrid common stock would recognize gain or loss for U.S. federal income tax purposes on each share of SendGrid common stock surrendered in the merger in an amount equal to the difference between (1) the fair market value of the merger consideration received in exchange for such surrendered share upon completion of the merger and (2) the holder's basis in the share of SendGrid common stock surrendered. Any gain or loss recognized would be long-term capital gain or loss if the U.S. holder's holding period in a particular block of SendGrid common stock exceeds one year at the effective time of the merger. Long-term capital gain of non-corporate U.S. holders (including individuals) is taxed at reduced U.S. federal income tax rates. The deductibility of capital losses is subject to limitations. For a more complete discussion of the material U.S. federal income tax consequences of the merger, please carefully review the information set forth in the section entitled "Material U.S. Federal Income Tax Consequences".

Risk Factors Relating to Twilio Following the Merger

Operational Risks

         Twilio expects to incur substantial expenses related to the merger.

        Twilio expects to incur substantial expenses in connection with completing the merger and integrating the business, operations, networks, systems, technologies, policies and procedures of SendGrid with those of Twilio. While Twilio has assumed that a certain level of transaction and integration expenses would be incurred, there are a number of factors beyond its control that could affect the total amount or the timing of its integration expenses. Many of the expenses that will be incurred, by their nature, are difficult to estimate accurately at the present time. Due to these factors, the transaction and integration expenses could be greater or could be incurred over a longer period of time than Twilio currently expects.

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         Following the merger, Twilio and SendGrid may be unable to successfully integrate their businesses and realize the anticipated benefits of the merger.

        The proposed transaction involves the merger of two companies which currently operate as independent public companies. The combined company will be required to devote significant management attention and resources to integrating the business practices and operations of Twilio and SendGrid in order to effectively realize synergies as a combined company, including opportunities to cross-sell existing products into each company's existing customer bases and more effectively launch and market products. Potential difficulties the combined company may encounter in the integration process include the following:

    the inability to successfully combine the businesses of Twilio and SendGrid in a manner that permits the combined company to realize the growth synergies anticipated to result from the merger, which would result in the anticipated benefits of the merger not being realized in the time frame currently anticipated or at all;

    lost sales and customers as a result of certain customers of either of the two companies deciding to terminate or reduce their business with the combined company;

    the complexities associated with managing the larger combined businesses and integrating personnel from the two companies, while at the same time attempting to (i) provide consistent, high quality products and services under a unified culture and (ii) focus on other on-going transactions;

    the additional complexities of combining two companies with different histories, regulatory restrictions, operating structures and markets;

    the failure to retain key employees of either of the two companies;

    potential unknown liabilities and unforeseen increased expenses, delays or regulatory conditions associated with the merger; and

    performance shortfalls at one or both of the two companies as a result of the diversion of management's attention caused by completing the merger and integrating the companies' operations.

        For all these reasons, you should be aware that it is possible that the integration process could result in the distraction of the combined company's management, the disruption of the combined company's ongoing business or inconsistencies in the combined company's products, services, standards, controls, procedures and policies, any of which could adversely affect the ability of the combined company to maintain relationships with customers, vendors and employees or to achieve the anticipated benefits of the merger, or could otherwise adversely affect the business and financial results of the combined company.

         If the combined company is unable to compete effectively, the results of operations of the combined company will be materially and adversely affected.

        The competitors of Twilio and SendGrid include large, technically competent and well capitalized companies, some of which have emerged as a result of industry consolidation, as well as "pure play" companies that have a single product focus. The competitiveness of Twilio or SendGrid, whether separately or as a combined company, is based on factors including technology, innovation, performance, price, quality, reliability, brand, reputation, distribution, range of products and services, ease of use of products, account relationships, customer training, service and support, and security. If the combined company is unable to compete based on such factors, the combined company's results of operations and business prospects could be harmed.

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        The combined company will have a large portfolio of services and will need to allocate financial, personnel and other resources across such services while competing with companies that have smaller portfolios or specialize in one or more of the combined company's service lines. As a result, the combined company may invest less in certain business areas than competitors do, and competitors may have greater financial, technical and marketing resources available to them compared to the resources allocated to the combined company's products and services that compete against their products and services. Industry consolidation may also affect competition by creating larger, more homogeneous and potentially stronger competitors in the markets in which the combined company operates.

        The combined company may face aggressive price competition and may have to lower prices of products and services to stay competitive, while simultaneously seeking to maintain or improve revenue and grow its subscriber base. The combined company's cash flows, results of operations and financial condition may be adversely affected by these and other industry-wide pricing pressures.

         The business operations of Twilio and SendGrid are subject to various and changing federal, state, local and foreign laws and regulations that could result in costs or sanctions that adversely affect the business and results of operations of the combined company.

        Both Twilio and SendGrid operate in an increasingly complex regulatory environment. Businesses in the countries in which Twilio and SendGrid operate are subject to local, legal and political environments and regulations including with respect to employment, tax, statutory supervision and reporting and trade restriction. These regulations and environments are also subject to change.

        Adjusting business operations to changing environments and regulations may be costly and could potentially render the particular business operations uneconomical, which may adversely affect the profitability of the combined company or lead to a change in the business operations.

        Notwithstanding the best efforts of the combined company, it may not be in compliance with all regulations in the countries in which it operates at all times and may be subject to sanctions, penalties or fines as a result. These sanctions, penalties or fines may materially and adversely impact the profitability of the combined company.

Other Risks

         The historical and unaudited pro forma condensed combined financial information included elsewhere in this joint proxy statement/prospectus may not be representative of Twilio's results after the merger, and accordingly, you have limited financial information on which to evaluate the combined company.

        Twilio and SendGrid will continue to operate as separate companies prior to the merger. Twilio and SendGrid have no prior history as a combined company. The historical financial statements of SendGrid may be different from those that would have resulted had SendGrid been operated as part of Twilio. The pro forma condensed combined financial information appearing elsewhere herein has been presented for informational purposes only and is not necessarily indicative of the financial position or results of operations that actually would have occurred had the merger been completed as of the dates indicated, nor is it indicative of the future operating results or financial position of the combined company. The unaudited pro forma condensed combined financial information reflects adjustments, which are based upon preliminary estimates, to allocate the aggregate consideration to SendGrid assets and liabilities. The aggregate consideration allocation reflected in the pro forma condensed combined financial information included in this joint proxy statement/prospectus is preliminary, and the final allocation of the aggregate consideration will be based upon the actual aggregate consideration and the fair value of the assets and liabilities of SendGrid as of the date of the completion of the merger. The unaudited pro forma condensed combined financial information does not (i) reflect future events that may occur after the merger, including the incurrence of costs related to the planned integration of SendGrid, any future non-recurring charges resulting from the merger and any termination of contracts by customers as a direct result of the merger, and (ii) consider potential effects of future market

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conditions on revenues or expense efficiencies. The unaudited pro forma financial information presented in this joint proxy statement/prospectus is based in part on certain assumptions regarding the merger that Twilio believes are reasonable under the circumstances. Twilio cannot assure you that the assumptions will prove to be accurate over time.

         If Twilio's goodwill or other intangible assets become impaired, it may be required to record a significant charge to earnings and reduce its stockholders' equity.

        As of September 30, 2018, a portion of Twilio's total consolidated assets reflected on the consolidated balance sheet incorporated by reference into this joint proxy/prospectus consisted of goodwill and intangible assets. Consummation of the merger is expected to result in Twilio recognizing additional goodwill and intangible assets on its consolidated balance sheet. See "The Merger—Accounting Treatment" beginning on page 153 of this joint proxy statement/prospectus. Intangible assets with finite lives will be amortized using the method that best reflects how their economic benefits are utilized or, if a pattern of economic benefits cannot be reliably determined, on a straight-line basis over their estimated useful lives. Goodwill and intangible assets with indefinite lives will not be amortized, but instead tested for potential impairment at least annually whenever events or changes in circumstances indicate that the carrying value may not be recoverable. If Twilio's goodwill or other intangible assets are determined to be impaired in the future, it may be required to record additional significant, non-cash charges to earnings during the period in which the impairment is determined to have occurred.

         The Twilio and SendGrid prospective financial information is inherently subject to uncertainties.

        While presented with numeric specificity, the Twilio and SendGrid prospective financial information provided in this document was prepared based on numerous variables and assumptions (including, but not limited to, those related to industry performance and competition and general business, economic, market and financial conditions and additional matters specific to Twilio or SendGrid business, as applicable) that are inherently subjective and uncertain and are largely beyond the control of the respective management of each. As a result, actual results may differ from the prospective financial information. Important factors that may affect actual results and cause these projected financial forecasts to not be achieved include, but are not limited to, risks and uncertainties relating to Twilio's or SendGrid's business, as applicable (including each company's ability to achieve strategic goals, objectives and targets over applicable periods) and general industry, business, competitive, technological and economic conditions. For more information see the sections entitled "The Merger—Certain Unaudited Prospective Financial Information Prepared by Twilio Management" beginning on page 110 and "The Merger—Certain Unaudited Prospective Financial Information Prepared by SendGrid Management"beginning on page 120.

         Twilio and SendGrid may be targets of securities class action and derivative lawsuits which could result in substantial costs and may delay or prevent the merger from being completed.

        Securities class action lawsuits and derivative lawsuits are often brought against public companies that have entered into merger agreements. Even if the lawsuits are without merit, defending against these claims could result in substantial costs and divert management time and resources. An adverse judgment could result in monetary damages, which could have a negative impact on Twilio's and SendGrid's respective liquidity and financial condition. Additionally, if a plaintiff is successful in obtaining an injunction prohibiting completion of the merger, then that injunction may delay or prevent the merger from being completed, which may adversely affect Twilio's and SendGrid's respective business, financial position and results of operations.

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Other Risks Related to Twilio's Business and SendGrid's business

        Twilio's and SendGrid's businesses are, and following completion of the transaction Twilio will continue to be, subject to the risks described above and in Twilio's Annual Report on Form 10-K for the fiscal year ended December 31, 2017, as amended and as updated by subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K and SendGrid's Annual Report on Form 10-K for the fiscal year ended December 31, 2017, as amended and as updated by subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, all of which are filed with the SEC and incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 199 for the location of information incorporated by reference in this joint proxy statement/prospectus.

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

        This joint proxy statement/prospectus and the documents incorporated by reference into this joint proxy statement/prospectus contain certain forecasts and other forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 with respect to the financial condition, results of operations, business strategies, operating efficiencies or synergies, revenue enhancements, competitive positions, growth opportunities, plans and objectives of the management of each of Twilio, SendGrid and, following the merger, the combined company, the merger and the markets for Twilio and SendGrid common stock and various other matters. Statements in this joint proxy statement/prospectus and the documents incorporated by reference herein that are not historical facts are hereby identified as "forward-looking statements" for the purpose of the safe harbor provided by Section 21E of the Exchange Act, and Section 27A of the Securities Act. These forward-looking statements, including, without limitation, those regarding the expected timing and benefits of the proposed transaction, such as efficiencies, cost savings, enhanced revenues, growth potential, market profile and financial strength, and the competitive ability and position of the combined company, and other statements identified by words such as "will," "estimates," "anticipates," "believes," "expects," "projects," "plans," "intends," "may," "should," "could," "seeks," "continue," "predict," "potentially" or the negative of these terms or other similar expressions, are subject to a number of risks, uncertainties and assumptions, many of which are beyond the control of Twilio and SendGrid. These forward-looking statements are based upon the judgment and assumptions of Twilio and SendGrid or, following the merger, the combined company as of the date of such statements concerning future developments and events, many of which are beyond their control. These forward-looking statements, and the assumptions upon which they are based, (i) are not guarantees of future results, (ii) are inherently speculative and (iii) are subject to a number of risks and uncertainties. Actual events and results may differ materially from those anticipated, estimated, projected or implied in those statements if one or more of these risks or uncertainties materialize, or if underlying assumptions prove incorrect.

        Forward-looking statements are found at various places throughout this joint proxy statement/prospectus, including in the sections entitled "The Merger—Certain Unaudited Prospective Financial Information Prepared by Twilio Management," "The Merger—Certain Unaudited Prospective Financial Information Prepared by SendGrid Management" and "Risk Factors." Important factors that could cause actual results to differ materially from those indicated by such forward-looking statements include those set forth in Twilio's and SendGrid's filings with the SEC, including Twilio's Annual Report on Form 10-K for the fiscal year ended December 31, 2017, as updated by subsequent Quarterly Reports on Form 10-Q and SendGrid's Annual Report on Form 10-K for the fiscal year ended December 31, 2017, as updated by the subsequent Quarterly Reports on Form 10-Q. These important factors also include those set forth under "Risk Factors" in this joint proxy statement/prospectus as well as, among others, risks and uncertainties relating to:

    the occurrence of any event, change, or other circumstances that could delay or prevent closing of the proposed merger or give rise to the termination of the merger agreement;

    the expected financial condition, results of operations, earnings outlook and prospects of Twilio, SendGrid and the combined company following completion of the merger;

    the ability of Twilio and SendGrid to maintain relationships with their respective employees, suppliers or customers as a result of the uncertainty surrounding the merger;

    the timing, outcome and results of integrating the operations of Twilio with those of SendGrid and the outcome of any anticipated benefits or potential synergies from combining the companies;

    the possibility that Twilio or SendGrid may be unable to obtain stockholder approval as required for the transaction or that the other conditions to the closing of the transaction may not be

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      satisfied, including that a governmental entity may prohibit, delay, or refuse to grant regulatory approval for the consummation of the proposed merger;

    risks that the transaction disrupts current plans and operations of Twilio or SendGrid, including the diversion of management time and other resources to transaction-related matters;

    the ability to timely recognize the benefits of the transaction, if at all;

    the amount of the costs, fees, expenses and charges related to the transaction;

    uncertainty as to the long-term value of Twilio's Class A common stock;

    changes in merger-related transaction costs, the amount of fees paid to financial advisors and the potential payments to SendGrid's named executive officers in connection with the merger; and

    the outcome of any legal proceedings that have been or may be instituted against Twilio, SendGrid, or others following announcement of the transactions contemplated by the merger agreement.

        Due to these risks and uncertainties, there can be no assurance that the proposed merger or any other transaction described herein will in fact be completed in the manner described or at all. You should be aware that new factors may emerge from time to time and it is not possible for Twilio or SendGrid to identify all such factors nor can Twilio or SendGrid predict the impact of each such factor on the proposed transaction or the combined company. You should not place undue reliance on these forward-looking statements, which speak only as of the date of this document. Unless legally required, Twilio and SendGrid undertake no obligation and each expressly disclaim any such obligation, to update publicly any forward-looking statements, whether as a result of new information, future events, changed circumstances or otherwise. Furthermore, any information about the intentions of Twilio, SendGrid or, following the merger, the combined company contained in any of their respective forward-looking statements reflect their intentions as of the date of such forward-looking statements, and are based upon, among other things, existing regulatory, technological, industry, competitive, economic and market conditions, and their assumptions as of such date. Twilio, SendGrid or, following the merger, the combined company may change their intentions, strategies or plans at any time and without notice, based upon any changes in such factors or assumptions or otherwise.

Prospective Financial Information

        The prospective financial information included in this document was not prepared with a view toward public dissemination or compliance with published guidelines of the SEC or the guidelines established by the American Institute of Certified Public Accountants for preparation or presentation of prospective financial information. The prospective financial information included in this document has been prepared by, and is the responsibility of, Twilio's or SendGrid's management, as applicable.

        KPMG LLP has not audited, reviewed, examined, compiled nor applied agreed-upon procedures with respect to the accompanying prospective financial information and, accordingly, KPMG LLP does not express an opinion or any other form of assurance with respect thereto. The KPMG LLP reports incorporated by reference in this joint proxy statement/prospectus relate only to the previously issued financial statements of SendGrid and Twilio, respectively. Such reports do not extend to the prospective financial information and should not be read to do so.

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THE TWILIO SPECIAL MEETING

Date, Time and Place of the Twilio Special Meeting

        The special meeting of Twilio stockholders 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.

Purpose of the Twilio Special Meeting

        At the Twilio special meeting, Twilio stockholders will be asked to consider and vote upon the following proposals:

    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, 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 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 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.

Recommendation of the Twilio Board

        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.

Record Date for the Twilio Special Meeting; Stock Entitled to Vote

        Only 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, the record date for the Twilio special meeting, will be entitled to notice of, and to vote at, the Twilio special meeting and any postponements or adjournments thereof. You may cast 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, including (i) shares held directly in your name as the stockholder of record and (ii) shares held for you as the beneficial owner in street name through a broker, bank, or other nominee.

        On the Twilio record date, there were outstanding a total of 80,667,248 shares of Twilio Class A common stock and 19,349,115 shares of Twilio Class B common stock entitled to vote at the Twilio special meeting.

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Solicitation of Proxies; Revocability of Proxies

        The cost of proxy solicitation for the Twilio special meeting and expenses for the filing, printing and mailing of this joint proxy statement/prospectus will be borne by Twilio. In addition to the use of the mail, proxies may be solicited by officers and directors and regular employees of Twilio, without additional remuneration, by personal interview, telephone, electronic communication or otherwise. Twilio will also request brokerage firms, nominees, custodians and fiduciaries to forward proxy materials to the beneficial owners of shares held of record on the Twilio record date and will provide customary reimbursement to such firms for the cost of forwarding these materials. Twilio has retained Innisfree M&A Incorporated to assist in its solicitation of proxies and has agreed to pay them a fee of up to $25,000, plus reasonable expenses, for these services.

        If you are a holder of record on the record date for the Twilio special meeting, you have the power to revoke your proxy at any time before your proxy is voted at the Twilio special meeting. You can revoke your proxy 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 prior to your shares being voted. If your shares are held in street name by your broker or nominee, you should contact them to change your vote.

Quorum

        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.

Vote Required

    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).

    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).

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        The Twilio bylaws provide that the chairperson of the Twilio special meeting may, if necessary, adjourn the Twilio special meeting for the purpose of soliciting additional proxies (whether or not a quorum exists).

Twilio Voting Agreements

        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 agreements are attached to this joint proxy statement/prospectus as Annexes F and G.

Abstentions and Broker Non-Votes

        If you are a Twilio stockholder, abstentions have the effect of a vote against the stock issuance proposal and, if necessary, the adjournment proposal. Broker "non-votes" have no effect on the outcome of the 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. If you fail to cast a vote or deliver a proxy card, it will also make it more difficult to meet the quorum requirement with respect to organizing the meeting.

Voting Power of Twilio's Directors and Executive Officers

        On the Twilio record date, 0.6% of the outstanding Twilio Class A common stock and 68.8% of the outstanding Twilio Class B common stock was held by Twilio directors and executive officers and their respective affiliates. Twilio currently expects that its directors and executive officers will vote their shares in favor of the issuance of Twilio Class A common stock to SendGrid stockholders in connection with the merger.

Attending the Twilio Special Meeting

        All holders of Twilio Class A common stock and Twilio Class B common stock, including stockholders of record and stockholders who hold shares through banks, brokers or other nominees, are invited to attend the Twilio special meeting. Stockholders of record can vote in person at the special meeting. If you plan to attend the special meeting, you must hold your shares in your own name or

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have a letter or an account statement issued by the record holder of your shares confirming your ownership, and you must bring a form of personal photo identification with you to be admitted. Twilio reserves the right to refuse admittance to anyone without proper proof of share ownership and without proper photo identification. Even if you plan to attend the Twilio special meeting, Twilio recommends that you also submit your proxy or voting instructions by mail, or by telephone or on the Internet as described in your proxy card so that your vote will be counted if you later decide not to attend the meeting.

        Subject to space availability and certain security procedures, all Twilio stockholders as of the record date for the Twilio special meeting, or their duly appointed proxies, may attend the Twilio special meeting. Each person attending the Twilio special meeting must have proof of ownership of the Twilio Class A common stock and/or Twilio Class B common stock that they own, as well as a valid government-issued photo identification, such as a driver's license or passport, to be admitted to the meeting. If you hold your shares of Twilio Class A common stock and/or Twilio Class B common stock in your name as a stockholder of record, you will need proof of ownership of such shares. If your shares of Twilio Class A common stock and/or Twilio Class B common stock are held in "street name" in the name of a bank, broker, or other nominee and you plan to attend the Twilio special meeting, you must present 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 Class A common stock and/or Twilio Class B common stock on the Twilio record date, to be admitted to the Twilio special meeting.

Voting of Proxies by Record Stockholders

        A proxy card is enclosed for use by Twilio stockholders of record. Twilio requests that its record stockholders sign the accompanying proxy and return it promptly in the enclosed postage-paid envelope. You may also vote your shares by telephone or through the Internet. Information and applicable deadlines for voting by telephone or through the Internet are set forth on the enclosed proxy card. Shares of Twilio Class A 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.

        At the date hereof, Twilio management has no knowledge of any business that will be presented for consideration at the special meeting and which would be required to be set forth in this joint proxy statement/prospectus other than the matters set forth in Twilio's accompanying Notice of Special Meeting of Stockholders. In accordance with Twilio's bylaws and Delaware law, business transacted at the Twilio special meeting will be limited to those matters set forth in such notice. Nonetheless, if any other matter is properly presented at the Twilio special meeting for consideration, it is intended that the persons named in the enclosed proxy and acting thereunder will vote in accordance with their best judgment on such matter.

        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.

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Shares Held in Street Name

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

        If you hold your Twilio Class A common stock and/or Twilio Class B common stock in street name and you do not instruct your broker on how to vote any of your shares, your broker may not vote those shares. For a discussion of the consequences of such broker non-votes, see "The Twilio Special Meeting—Abstentions and Broker Non-Votes" beginning on page 52 of this joint proxy statement/prospectus.

Revocability of Proxies and Changes to a Twilio Stockholder's Vote

        If you are a holder of shares of Twilio Class A common stock and/or Twilio Class B common stock as of the record date for the Twilio special meeting, you have the power to revoke your proxy at any time before your proxy is voted at the Twilio special meeting. You can revoke your proxy in one of four ways:

    you can send a signed notice of revocation that is received by Twilio prior to your shares being voted, stating that you would like to revoke your proxy, to Twilio's corporate secretary at Twilio's corporate headquarters, 375 Beale Street, Suite 300, San Francisco, California 94105;

    you can grant a new, valid proxy bearing a later date (by Internet, telephone or mail) that is received by Twilio prior to your shares being voted;

    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 wish to change your vote at the Twilio special meeting, you must vote by ballot at such meeting or if you wish to revoke your vote at the Twilio special meeting, you must bring a written notice of revocation to the Secretary of the Twilio special meeting prior to the voting at the Twilio special meeting.

        The latest dated completed proxy will be the one that counts. Written notices of revocation and other communications with respect to the revocation of any proxies should be addressed to:

      Twilio Inc.
      375 Beale Street, Suite 300
      San Francisco, California 94105
      Attn: Corporate Secretary

        If you are a Twilio stockholder whose shares of Twilio Class A common stock and/or Twilio Class B common stock are held in "street name" by a bank, broker, or other nominee, you may revoke your proxy or voting instructions and vote your shares in person at the Twilio special meeting only in accordance with applicable rules and procedures as employed by your bank, broker, or other nominee. If your shares are held in "street name" in an account at a bank, broker, or other nominee, you must follow the directions you receive from your bank, broker, or other nominee in order to change or

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revoke your proxy or voting instructions and should contact your bank, broker, or other nominee to do so.

Adjournments

        Although it is not currently expected, the Twilio special meeting may be adjourned for the purpose of soliciting additional proxies if Twilio has not received sufficient proxies to constitute a quorum or sufficient votes for approval of the Twilio stock issuance proposal. Adjourning the Twilio special meeting 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). The Twilio bylaws provide that the chairperson of the Twilio special meeting may, if necessary, adjourn the Twilio special meeting for the purpose of soliciting additional proxies (whether or not a quorum exists). Pursuant to the Twilio bylaws, notice need not be given of any such adjourned meeting if the time and place thereof are announced at the meeting at which adjournment is taken. If the time and place of an adjourned meeting (and means of remote communications, if any, by which stockholders and proxy holders may be deemed to be present in person and vote at such adjourned meeting) are announced at the original convening of the Twilio special meeting, no notice of an adjourned meeting need be given unless the adjournment is for more than 30 days or if, after the adjournment, a new record date is fixed for the adjourned meeting. If the Twilio special meeting is adjourned, stockholders who have already sent in their proxies will be allowed to revoke them at any time prior to their use. The merger agreement provides that the Twilio special meeting will not be adjourned to a date that is more than 15 calendar days after the date for which the Twilio special meeting was originally scheduled.

Postponements

        At any time prior to convening the Twilio special meeting, the Twilio Board may postpone the Twilio special meeting for any reason without the approval of the Twilio stockholders. The merger agreement provides that the Twilio special meeting will not be postponed to a date that is more than 15 calendar days after the date for which the Twilio special meeting was originally scheduled. Although it is not currently expected, the Twilio Board may postpone the Twilio special meeting for the purpose of soliciting additional proxies if Twilio has not received sufficient proxies to constitute a quorum or sufficient votes for approval of the Twilio stock issuance proposal. If the Twilio special meeting is postponed, stockholders who have already sent in their proxies will be allowed to revoke them at any time prior to their use.

Stockholder List

        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.

Tabulation of Votes

        A representative of Twilio's mailing and tabulating agent, Broadridge Financial Solutions, will tabulate the votes and act as inspector of elections.

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How You Can Reduce the Number of Copies of Twilio's Proxy Materials You Receive

        Twilio has adopted a procedure approved by the Securities and Exchange Commission called "householding." Under this procedure, stockholders of record who have the same address and last name and who do not participate in electronic delivery of proxy materials will receive only one copy of the proxy materials, unless one or more of these stockholders notifies Twilio that they wish to continue receiving individual copies. This procedure reduces Twilio's printing costs and postage fees. Stockholders who wish to participate in householding will continue to receive separate proxy cards.

        If you are eligible for householding, but you and other stockholders of record with whom you share an address currently receive multiple copies of the proxy materials, or if you hold stock in more than one account, and, in either case, you wish to receive only a single copy of the proxy materials for your household, please contact your broker.

        If you participate in householding and wish to receive a separate copy of the proxy materials, or if you do not wish to continue to participate in householding and prefer to receive separate copies of the proxy materials in the future, please contact your broker or Twilio. Direct your written request to Twilio Inc., Investor Relations, 375 Beale Street, Suite 300, San Francisco or contact Investor Relations at (415) 390-2337.

        Beneficial owners can request information about householding from their banks, brokers, or other holders of record.

Assistance

        If you need assistance in completing your proxy card or have questions regarding the Twilio special meeting, please contact Innisfree M&A Incorporated, the proxy solicitor for Twilio, at 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.

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TWILIO PROPOSALS

Twilio Proposal 1: The Twilio Stock Issuance Proposal

        Twilio stockholders are asked to approve the issuance of Twilio Class A common stock to SendGrid stockholders in connection with the merger contemplated by the merger agreement. Twilio stockholders should carefully read this joint proxy statement/prospectus in its entirety, including the documents incorporated by reference and the merger agreement, for more detailed information concerning the merger agreement and the Twilio stock issuance proposal. For a detailed discussion of the terms of the merger agreement and the merger, including the proposed Twilio stock issuance, see the information about the merger and the merger agreement throughout this joint proxy statement/prospectus, including the information set forth in the section entitled "The Merger Agreement" beginning on page 68 of this joint proxy statement/prospectus. A copy of the merger agreement, as amended, is attached as Annex A to this joint proxy statement/prospectus.

        Approval of the Twilio stock issuance proposal is a condition to completion of the merger. If the Twilio stock issuance proposal is not approved, the merger will not occur. For a detailed discussion of the conditions of the merger, see "The Merger Agreement—Conditions to Completion of the Merger" beginning on page 85 of this joint proxy statement/prospectus.

        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 represented by proxy entitled to vote on such matter at the Twilio special meeting (provided that a quorum exists).

        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.

IF YOU ARE A TWILIO STOCKHOLDER, THE TWILIO BOARD
RECOMMENDS THAT YOU VOTE "FOR" THE PROPOSAL TO ISSUE SHARES OF
TWILIO CLASS A COMMON STOCK IN THE MERGER.

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Twilio Proposal 2: The Twilio Adjournment Proposal

        This proposal would permit the Twilio Board to adjourn from time to time the Twilio special meeting, if necessary, to solicit additional proxies if there are not sufficient votes to approve the Twilio stock issuance proposal.

        If the time and place of an adjourned meeting (and means of remote communications, if any, by which stockholders and proxy holders may be deemed to be present in person and vote at such adjourned meeting) are announced at the original convening of the Twilio special meeting, no notice of an adjourned meeting need be given unless the adjournment is for more than 30 days or if, after the adjournment, a new record date is fixed for the adjourned meeting, in which case notice of the adjourned meeting will be given to Twilio stockholders of record entitled to vote at the adjourned meeting. At any adjourned meeting, any business may be transacted which might have been transacted at the original meeting.

        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

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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.

IF YOU ARE A TWILIO STOCKHOLDER, THE TWILIO BOARD RECOMMENDS THAT YOU
VOTE "FOR" THE PROPOSAL TO PERMIT THE TWILIO BOARD TO ADJOURN THE TWILIO
SPECIAL MEETING.

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THE SENDGRID SPECIAL MEETING

Date, Time and Place of the SendGrid Special Meeting

        The special meeting of SendGrid stockholders 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.

Purpose of the SendGrid Special Meeting

        At the SendGrid special meeting, SendGrid stockholders will be asked to consider and vote upon the following proposals:

    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 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 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.

Recommendation of the SendGrid Board

        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 was made unanimously by the SendGrid Board with the exception of director Byron Deeter, who 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.

Record Date for the SendGrid Special Meeting; Stock Entitled to Vote

        Only holders of record of shares of SendGrid common stock at the close of business on December 13, 2018, the record date for the SendGrid special meeting, will be entitled to notice of, and to vote at, the SendGrid special meeting and any postponements or adjournments thereof. You may cast one vote for each share of SendGrid common stock that you owned as of the SendGrid record date, including (i) shares held directly in your name as the stockholder of record and (ii) shares held for you as the beneficial owner in street name through a broker, bank, or other nominee.

        On the SendGrid record date, there were outstanding a total of 47,659,204 shares of SendGrid common stock entitled to vote at the SendGrid special meeting.

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Solicitation of Proxies; Revocability of Proxies

        The cost of proxy solicitation for the SendGrid special meeting will be borne by SendGrid. In addition to the use of the mail, proxies may be solicited by officers and directors and regular employees of SendGrid, without additional remuneration, by personal interview, telephone, electronic communication or otherwise. SendGrid will also request brokerage firms, nominees, custodians and fiduciaries to forward proxy materials to the beneficial owners of shares held of record on the SendGrid record date and will provide customary reimbursement to such firms for the cost of forwarding these materials. SendGrid has retained MacKenzie Partners, Inc. to assist in its solicitation of proxies and has agreed to pay them a fee of $15,000 and potentially additional fees under certain circumstances, plus reasonable expenses, for these services.

        If you are a holder of record on the record date for the SendGrid special meeting, you have the power to revoke your proxy at any time before your proxy is voted at the SendGrid special meeting. You can revoke your proxy 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 SendGrid prior to your shares being voted.

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

Quorum

        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.

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        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.

Vote Required

    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.

    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.

    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.

SendGrid Voting Agreements

        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 December 13, 2018, 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.

Abstentions and Broker Non-Votes

        If you are a SendGrid stockholder, 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. 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 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.

Voting Power of SendGrid's Directors and Executive Officers

        On the SendGrid record date, 20% of the outstanding SendGrid common stock was held by SendGrid directors and executive officers and their respective affiliates. SendGrid currently expects that its directors and executive officers will vote their shares in favor of the SendGrid merger proposal.

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Attending the SendGrid Special Meeting

        All holders of SendGrid common stock, including stockholders of record and stockholders who hold shares through banks, brokers or other nominees, are invited to attend the SendGrid special meeting. Stockholders of record can vote in person at the special meeting. If you plan to attend the special meeting, you must hold your shares in your own name or have a letter or an account statement issued by the record holder of your shares confirming your ownership, and you must bring a form of personal photo identification with you to be admitted. SendGrid reserves the right to refuse admittance to anyone without proper proof of share ownership and without proper photo identification.

        Subject to space availability and certain security procedures, all SendGrid stockholders as of the record date for the SendGrid special meeting, or their duly appointed proxies, may attend the SendGrid special meeting. Shares of SendGrid common stock held in your name as the stockholder of record may be voted by you in person at the SendGrid special meeting. Shares of SendGrid common stock held beneficially in street name may be voted by you in person at the SendGrid special meeting only if you obtain a legal proxy from the bank, broker, or other nominee that holds your shares of SendGrid common stock giving you the right to vote such shares. Each person attending the SendGrid special meeting must have proof of ownership of the SendGrid common stock that they own, as well as a valid government-issued photo identification, such as a driver's license or passport, to be admitted to the meeting. If you hold your shares of SendGrid common stock in your name as a stockholder of record, you will need proof of ownership of such shares. If your shares of SendGrid common stock are held in "street name" in the name of a bank, broker, or other nominee and you plan to attend the SendGrid special meeting, you must present acceptable proof of ownership, such as a letter from your broker or an account statement stating or showing that you beneficially owned shares of SendGrid common stock on the SendGrid record date, to be admitted to the SendGrid special meeting. Even if you plan to attend the SendGrid special meeting, SendGrid recommends that you also submit your proxy or voting instructions by mail, or by telephone or on the Internet as described in your proxy card so that your vote will be counted if you later decide not to attend the meeting.

Voting of Proxies by Record Stockholders

        A proxy card is enclosed for use by SendGrid stockholders of record. SendGrid requests that its record stockholders sign the accompanying proxy and return it promptly in the enclosed postage-paid envelope. You may also vote your shares by telephone or through the Internet. Information and applicable deadlines for voting by telephone or through the Internet are set forth on the enclosed proxy card. 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.

        At the date hereof, SendGrid management has no knowledge of any business that will be presented for consideration at the special meeting and which would be required to be set forth in this joint proxy statement/prospectus other than the matters set forth in SendGrid's accompanying Notice of Special Meeting of Stockholders. In accordance with SendGrid's bylaws and Delaware law, business transacted at the SendGrid special meeting will be limited to those matters set forth in such notice. Nonetheless, if any other matter is properly presented at the SendGrid special meeting for consideration, it is intended that the persons named in the enclosed proxy and acting thereunder will vote in accordance with their best judgment on such matter.

        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

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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.

Shares Held in Street Name

        If you hold your shares of SendGrid common stock in a stock brokerage account or if your shares are held by a bank or 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 wish them to be counted. Please follow the voting instructions provided by your broker, bank or nominee. Please note that you may not vote shares held in street name by returning a proxy card directly to SendGrid or by voting in person at the SendGrid special meeting. Further, brokers who hold shares of SendGrid common stock on behalf of their customers may not vote those shares without specific instructions from their customers.

        If you hold your SendGrid common stock in street name and you do not instruct your broker on how to vote any of your shares, your broker may not vote those shares. For a discussion of the consequences of such broker non-votes, see "The SendGrid Special Meeting—Abstentions and Broker Non-Votes" beginning on page 61 of this joint proxy statement/prospectus.

Revocability of Proxies and Changes to a SendGrid Stockholder's Vote

        If you are a holder of shares of SendGrid common stock as of the record date for the SendGrid special meeting, you have the power to revoke your proxy at any time before your proxy is voted at the SendGrid special meeting. You can revoke your proxy in one of four ways:

    you can send a signed notice of revocation that is received by SendGrid prior to your shares being voted, stating that you would like to revoke your proxy, to SendGrid's corporate secretary at SendGrid's corporate headquarters, 1801 California Street, Suite 500, Denver, Colorado 80202;

    you can grant a new, valid proxy bearing a later date (by Internet, telephone or mail) that is received by SendGrid prior to your shares being voted;

    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 wish to change your vote at the SendGrid special meeting, you must vote by ballot at such meeting or if you wish to revoke your vote at the SendGrid special meeting, you must bring a written notice of revocation to the Secretary of the SendGrid special meeting prior to the voting at the SendGrid special meeting.

        The latest dated completed proxy will be the one that counts. Written notices of revocation and other communications with respect to the revocation of any proxies should be addressed to:

    SendGrid Inc.
    1801 California Street, Suite 500
    Denver, Colorado 80202
    Attn: Corporate Secretary

        If you are a SendGrid stockholder whose shares of common stock are held in "street name" by a bank, broker, or other nominee, you may revoke your proxy or voting instructions and vote your shares in person at the SendGrid special meeting only in accordance with applicable rules and procedures as employed by your bank, broker, or other nominee. If your shares are held in "street name" in an

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account at a bank, broker, or other nominee, you must follow the directions you receive from your bank, broker, or other nominee in order to change or revoke your proxy or voting instructions and should contact your bank, broker, or other nominee to do so.

Adjournments

        Although it is not currently expected, the SendGrid special meeting may be adjourned for the purpose of soliciting additional proxies if SendGrid has not received sufficient proxies to constitute a quorum or sufficient votes for approval of the SendGrid merger proposal. If a quorum is not present, the chairperson of the SendGrid special meeting or holders of a majority of the votes present at the SendGrid special meeting may adjourn the special meeting. If a quorum is present, the SendGrid special meeting may be adjourned if sufficient votes are cast in favor of the SendGrid adjournment proposal. Pursuant to the SendGrid bylaws, notice need not be given of any such adjourned meeting if the time and place thereof are announced at the meeting at which adjournment is taken. If the adjournment is for more than 30 days or if after the adjournment a new record date is fixed for the adjourned meeting, a notice of the adjourned meeting shall be given to each stockholder of record entitled to vote at the SendGrid special meeting. At any adjourned meeting, any business may be transacted which might have been transacted at the original meeting. If the SendGrid special meeting is adjourned, stockholders who have already sent in their proxies will be allowed to revoke them at any time prior to their use. The merger agreement provides that the SendGrid special meeting will not be adjourned to a date that is more than 15 calendar days after the date for which the SendGrid special meeting was originally scheduled.

Stockholder List

        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.

Tabulation of Votes

        A representative of SendGrid's mailing and tabulating agent, Broadridge Financial Solutions, will tabulate the votes and SendGrid's corporate secretary will act as inspector of elections.

How You Can Reduce the Number of Copies of SendGrid's Proxy Materials You Receive

        SendGrid has adopted a procedure approved by the Securities and Exchange Commission called "householding." Under this procedure, stockholders of record who have the same address and last name and who do not participate in electronic delivery of proxy materials will receive only one copy of the proxy materials, unless one or more of these stockholders notifies SendGrid that they wish to continue receiving individual copies. This procedure reduces SendGrid's printing costs and postage fees. Stockholders who wish to participate in householding will continue to receive separate proxy cards.

        If you are eligible for householding, but you and other stockholders of record with whom you share an address currently receive multiple copies of the proxy materials, or if you hold stock in more than one account, and, in either case, you wish to receive only a single copy of the proxy materials for your household, please contact your broker.

        If you participate in householding and wish to receive a separate copy of the proxy materials, or if you do not wish to continue to participate in householding and prefer to receive separate copies of the proxy materials in the future, please contact your broker or SendGrid. Direct your written request to

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SendGrid, Inc., Investor Relations, 1801 California Street, Suite 500, Denver, Colorado 80202 or contact Investor Relations at (888) 985-7363.

        Beneficial owners can request information about householding from their banks, brokers, or other holders of record.

Assistance

        If you need assistance in completing your proxy card or have questions regarding the SendGrid special meeting, please contact MacKenzie Partners, Inc., the proxy solicitor for SendGrid, by telephone toll-free at 1-800-322-2885.

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SENDGRID PROPOSALS

SendGrid Proposal 1: The SendGrid Merger Proposal

        SendGrid stockholders are asked to approve the adoption of the merger agreement. SendGrid stockholders should carefully read this joint proxy statement/prospectus in its entirety, including the documents incorporated by reference and the merger agreement, for more detailed information concerning the merger agreement and the SendGrid merger proposal. For a detailed discussion of the terms of the merger agreement and the merger, see the information about the merger and the merger agreement throughout this joint proxy statement/prospectus, including the information set forth in the section entitled "The Merger Agreement" beginning on page 68 of this joint proxy statement/prospectus. A copy of the merger agreement is attached as Annex A to this joint proxy statement/prospectus.

        Approval of the SendGrid merger proposal is a condition to completion of the merger. If the SendGrid merger proposal is not approved, the merger will not occur. For a detailed discussion of the conditions of the merger, see "The Merger Agreement—Conditions to Completion of the Merger" beginning on page 85 of this joint proxy statement/prospectus.

        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 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 and all of such shares will be voted as recommended by the SendGrid Board.

        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.

IF YOU ARE A SENDGRID STOCKHOLDER, THE SENDGRID BOARD
RECOMMENDS THAT YOU VOTE "FOR" THE PROPOSAL TO ADOPT THE MERGER
AGREEMENT.

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SendGrid Proposal 2: The SendGrid Compensation Proposal

        Under Section 14A of the Exchange Act and the applicable Securities and Exchange Commission rules issued thereunder, SendGrid is required to submit a proposal to its stockholders 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. This compensation is summarized in the table captioned "Financial Interests of SendGrid Directors and Executive Officers in the Merger" beginning on page 140 of this joint proxy statement/prospectus, including the footnotes to the table and narrative disclosures set forth in the section. The SendGrid Board encourages you to review carefully the named executive officer merger-related compensation information disclosed in this joint proxy statement/prospectus. The vote on the compensation proposal is a vote separate and apart from the vote on the merger proposal. Accordingly, you may vote to approve the merger proposal and vote not to approve the compensation proposal and vice versa. Because the vote on the compensation proposal is advisory

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only, it will not be binding on either SendGrid or Twilio. Accordingly, if the merger agreement is adopted and the merger is completed, the compensation will be payable, subject only to the conditions applicable thereto, regardless of the outcome of the vote on the 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 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 and all of such shares will be voted as recommended by the SendGrid Board.

IF YOU ARE A SENDGRID STOCKHOLDER, THE SENDGRID BOARD RECOMMENDS THAT YOU VOTE "FOR" THE 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.

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SendGrid Proposal 3: The SendGrid Adjournment Proposal

        This proposal would permit the SendGrid Board to adjourn from time to time the SendGrid special meeting, if necessary, to solicit additional proxies if there are not sufficient votes to approve the SendGrid merger proposal.

        Pursuant to the SendGrid bylaws, notice need not be given of any such adjourned meeting if the time and place thereof are announced at the meeting at which adjournment is taken. If the adjournment is for more than 30 days or if after the adjournment a new record date is fixed for the adjourned meeting, a notice of the adjourned meeting shall be given to each stockholder of record entitled to vote at the SendGrid special meeting. At any adjourned meeting, any business may be transacted which might have been transacted at the original meeting.

        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 represented by properly executed, timely received and unrevoked proxies will be voted in accordance with the instructions indicated thereon. 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 and all of such shares will be voted as recommended by the SendGrid Board.

IF YOU ARE A SENDGRID STOCKHOLDER, THE SENDGRID BOARD RECOMMENDS THAT YOU VOTE "FOR" THE PROPOSAL TO PERMIT THE SENDGRID BOARD TO ADJOURN THE SENDGRID SPECIAL MEETING.

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THE MERGER AGREEMENT

        The following section summarizes the material provisions of the merger agreement, which is included in this joint proxy statement/prospectus as Annex A and is incorporated herein by reference in its entirety. The rights and obligations of Twilio and SendGrid are governed by the express terms and conditions of the merger agreement and not by this summary or any other information contained in this joint proxy statement/prospectus. Twilio and SendGrid stockholders are urged to read the merger agreement carefully and in its entirety as well as this joint proxy statement/prospectus before making any decisions regarding the merger, including the adoption by the SendGrid stockholders of the merger agreement or the approval by the Twilio stockholders of the issuance of Twilio Class A common stock in connection with the merger. This summary is qualified in its entirety by reference to the merger agreement.

        The merger agreement is described in this joint proxy statement/prospectus to provide you with information regarding its terms and is not intended to provide any factual information about Twilio or SendGrid. The merger agreement contains representations and warranties that the parties made to each other as of the date of the merger agreement or other specific dates, solely for purposes of the contract between the parties, and those representations and warranties should not be relied upon by any other person. The assertions embodied in those representations and warranties are subject to important qualifications and limitations agreed to by the parties in connection with negotiating the merger agreement. Accordingly, the representations and warranties may not be accurate or complete characterizations of the actual state of facts at any time. In particular, the representations and warranties:

    may not be intended to establish matters of fact, but rather to allocate the risk between the parties in the event the statements contained in the representations and warranties prove to be inaccurate;

    have been modified in important part by certain underlying disclosures that were made between the parties in connection with the negotiation of the merger agreement, which are not reflected in the merger agreement itself or publicly filed; and

    are subject to contractual standards of materiality different from what is generally applicable to you or other investors.

        The merger agreement has been included as Annex A to this joint proxy statement/prospectus to provide investors and security holders with information regarding its terms. It is not intended to provide any other financial information about Twilio, SendGrid, or their respective subsidiaries and affiliates. The representations, warranties and covenants contained in the merger agreement were made only for purposes of that agreement and as of specific dates, were solely for the benefit of the parties to the merger agreement, may be subject to limitations agreed upon by the parties, including being qualified by confidential disclosures made for the purposes of allocating contractual risk between the parties to the merger agreement instead of establishing these matters as facts, and may be subject to standards of materiality applicable to the contracting parties that differ from those applicable to investors. Twilio's stockholders and SendGrid's stockholders and other investors are not third-party beneficiaries under the merger agreement and should not rely on the representations, warranties and covenants or any description thereof as characterizations of the actual state of facts or condition of Twilio, SendGrid, or any of their respective subsidiaries or affiliates. Moreover, information concerning the subject matter of the representations, warranties and covenants may change after the date of the merger agreement, which subsequent information may or may not be fully reflected in public disclosures by Twilio and SendGrid.

        Accordingly, the representations and warranties and other provisions of the merger agreement should not be read alone, but instead should be read together with the information provided elsewhere in this joint proxy statement/prospectus and in the documents incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 199.

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Terms of the Merger; Merger Consideration

        Pursuant to the merger agreement, and in accordance with Delaware law, at the effective time of the merger, Merger Sub will be merged with and into SendGrid, with SendGrid continuing as a direct wholly owned subsidiary of Twilio.

        At the effective time of the merger, each share of SendGrid common stock issued and outstanding (other than shares owned by Twilio or Merger Sub or shares held in treasury), will be automatically converted into the right to receive 0.485 of a share of validly issued, fully paid and non-assessable shares of Twilio Class A common stock, par value $0.001 per share, which we refer to as the merger consideration.

        Twilio will not issue fractional shares of Twilio Class A common stock pursuant to the merger agreement. Instead, each SendGrid stockholder who otherwise would have been entitled to receive a fraction of a share of Twilio Class A common stock will receive cash in lieu thereof, as provided in the merger agreement.

        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.

Procedures for Exchanging SendGrid Common Stock in the Merger

        Prior to the effective time of the merger, Twilio shall designate a bank or trust company reasonably acceptable to SendGrid to act as the exchange agent in connection with the merger. At or prior to the effective time of the merger, Twilio or Merger Sub will deposit, or cause to be deposited, with the exchange agent (i) evidence of shares of Twilio Class A common stock issuable pursuant to the merger agreement in book-entry form equal to the aggregate merger consideration (excluding any cash in lieu of fractional shares payable pursuant to the merger agreement) and (ii) cash in immediately available funds in an amount sufficient to pay any dividends payable pursuant to the merger agreement, and an amount of cash in lieu of fractional shares payable pursuant to the merger agreement, in each case, for the sole benefit of the holders of shares of SendGrid common stock.

        Upon surrender of stock certificates accompanied by an executed letter of transmittal and other documents described in the instructions or, in the case of uncertificated shares, an "agent's message" in customary form, of SendGrid common stock for cancellation, a SendGrid stockholder will receive the following: (i) the share consideration to which such SendGrid stockholder is entitled and (ii) cash in lieu of fractional shares of Twilio Class A common stock, if any. SendGrid stockholders will not receive any fractional shares of Twilio Class A common stock pursuant to the merger. After the effective time of the merger, SendGrid will not register any transfers of the shares of SendGrid common stock. Shares of Twilio Class A stock issued in connection with the merger will be issued in uncertificated, book-entry form.

        After the effective time of the merger, shares of SendGrid common stock will no longer be issued and outstanding, will be canceled and will cease to exist, and (A) each certificate, if any, that previously represented SendGrid common stock and (B) each book-entry account formerly representing any uncertificated shares of SendGrid common stock will represent only the right to receive the merger consideration as described above. With respect to such shares of Twilio Class A common stock deliverable upon the surrender of SendGrid stock certificates, until holders of such SendGrid stock certificates have surrendered such stock certificates to the exchange agent for exchange, those holders will not receive dividends or distributions with respect to such shares of Twilio Class A common stock with a record date after the effective time of the merger.

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        Twilio stockholders need not take any action with respect to their stock certificates.

Completion of the Merger

        The closing of the merger will take place (a) at the offices of Goodwin Procter LLP, 100 Northern Avenue, Boston, Massachusetts 02210 as soon as reasonably practicable, and in no event later than two business days after the satisfaction or waiver of the conditions to the closing of the merger have been satisfied or waived (other than conditions that by their nature cannot be satisfied until the closing of the merger, which shall be required to be so satisfied or waived in accordance with the merger agreement upon the closing date of the merger) or (b) at such other time, date or place as Twilio and SendGrid may agree in writing. The merger will become effective upon the filing of the certificate of merger with the Secretary of State of the State of Delaware, in accordance with the laws of Delaware.

Representations and Warranties

        The merger agreement contains representations and warranties made by each of Twilio and SendGrid related to, among other things:

    due organization, good standing and the requisite corporate power and authority to carry on their respective businesses;

    subsidiaries and equity interests;

    capital structure and related matters;

    corporate power and authority to enter into the merger agreement and due execution, delivery and enforceability of the merger agreement;

    absence of conflicts with organizational documents, breaches of contracts and agreements, liens upon assets and violations of applicable law resulting from the execution and delivery of the merger agreement and consummation of the transactions contemplated by the merger agreement;

    absence of required governmental or other third-party consents in connection with execution and delivery of the merger agreement and consummation of the transactions contemplated by the merger agreement other than as specified in the merger agreement;

    SEC filings, financial statement compliance and absence of undisclosed liabilities (other than certain specified exceptions);

    internal controls and procedures;

    absence of certain changes or events and conduct of business in the ordinary course since January 1, 2018;

    litigation;

    in the case of SendGrid, employee benefits matters and ERISA compliance;

    in the case of SendGrid, employee and labor matters;

    compliance with laws;

    material contracts;

    in the case of SendGrid, environmental matters and compliance with environmental laws;

    in the case of SendGrid, anti-corruption and anti-bribery matters;

    tax matters and intended tax treatment of the merger;

    intellectual property;

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    compliance with privacy laws and data security;

    in the case of SendGrid, insurance and title to properties;

    accuracy and completeness of information supplied for the inclusion or incorporation by reference in this joint proxy statement/prospectus and, in the case of Twilio, the Form S-4;

    in the case of Twilio and Merger Sub, their obligations not being subject to, or conditioned on, the receipt or availability of any funds or financing;

    absence of brokers and other advisors;

    opinions of financial advisors; and

    absence of other representations and warranties.

        The merger agreement also contains certain representations and warranties of Twilio with respect to its direct, wholly owned subsidiary Merger Sub, including corporate organization, qualification to do business, no conflicts or violation and authority with respect to the execution and delivery of the merger agreement.

        Many of the representations and warranties in the merger agreement are qualified by a "knowledge," "materiality" or "material adverse effect" standard (that is, they will not be deemed to be untrue or incorrect unless their failure to be true or correct, individually or in the aggregate, would, as the case may be, be material or have a material adverse effect). For purposes of the merger agreement, a "material adverse effect" means, with respect to a party, any fact, circumstance, effect, change, event or development that, individually or in the aggregate, (i) materially adversely affects or would reasonably be expected to materially adversely affect the business, financial condition or results of operations of a party and its subsidiaries, taken as a whole, or (ii) would reasonably be expected to prevent or materially impair or delay the consummation of the transactions contemplated by the merger agreement.

        Clause (i) of the definition of "material adverse effect" excludes any fact, circumstance, effect, change, event or development to the extent that, either alone or combination, it results from or arises out of:

    changes or conditions generally affecting the industries in which such party and any of its subsidiaries operate, except to the extent such fact, circumstance, effect, change, event or development has a materially disproportionate adverse effect on such party and its subsidiaries, taken as a whole, relative to others in such industries in respect of the business conducted in such industries;

    general economic or political conditions or securities, credit, financial or other capital markets conditions, in each case in the United States or any foreign jurisdiction, except to the extent such fact, circumstance, effect, change, event or development has a materially disproportionate adverse effect on such party and its subsidiaries, taken as a whole, relative to others in the industries in which such party or any of its subsidiaries operate in respect of the business conducted in such industries;

    any failure, in and of itself, by such party to meet any internal or published projections, forecasts, estimates or predictions in respect of revenues, earnings or other financial or operating metrics for any period (it being understood that the facts or occurrences giving rise to or contributing to such failure may be deemed to constitute, or be taken into account in determining whether there has been, or is reasonably expected to be, a material adverse effect);

    the public announcement or pendency of the transactions contemplated in the merger agreement, including the impact thereof on the relationships, contractual or otherwise, of such party and its subsidiaries with employees, labor unions, customers, suppliers or partners;

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    any change, in and of itself, in the market price or trading volume of such party's securities or in its credit ratings (it being understood that the facts or occurrences giving rise to or contributing to such change may be deemed to constitute, or be taken into account in determining whether there has been, or is reasonably expected to be, a material adverse effect);

    any change in applicable law, regulation or GAAP (or authoritative interpretation thereof), except to the extent such fact, circumstance, effect, change, event or development has a materially disproportionate adverse effect on such party and its subsidiaries, taken as a whole, relative to others in the industries in which such party and its subsidiaries operate in respect of the business conducted in such industries;

    geopolitical conditions, the outbreak or escalation of hostilities, any acts of war (whether or not declared), sabotage or terrorism, or any escalation or worsening of any such acts of war, sabotage or terrorism threatened or underway as of the date of the merger agreement, except to the extent such fact, circumstance, effect, change, event or development has a materially disproportionate adverse effect on such party and its subsidiaries, taken as a whole, relative to others in the industries in which such party and any of its subsidiaries operate in respect of the business conducted in such industries;

    any hurricane, tornado, flood, earthquake or other natural disaster, except to the extent such fact, circumstance, effect, change, event or development has a materially disproportionate adverse effect on such party and its subsidiaries, taken as a whole, relative to others in the industries in which such party and any of its subsidiaries operate in respect of the business conducted in such industries;

    any litigation arising from allegations of a breach of fiduciary duty or other violation of applicable law relating to the merger agreement or the transactions contemplated thereby; or

    any taking of any action not required by the merger agreement at the written request of the other party or parties thereto or any action expressly required to be taken under the merger agreement.

        The representations and warranties contained in the merger agreement will not survive the consummation of the merger, but they form the basis of specified conditions to the parties' obligations to complete the merger.

Conduct of Business

        Each of Twilio and SendGrid has agreed to certain covenants in the merger agreement restricting the conduct of its business between the date of the merger agreement and the effective time of the merger. In general, each of Twilio and SendGrid has agreed to conduct its business in all material respects in the ordinary course of business and in a manner consistent with past practice and in all material respects in compliance with applicable laws. Further, SendGrid has agreed to use reasonable best efforts to preserve intact its business organization and use commercially reasonable efforts to preserve advantageous business relationships and keep available the services of its current officers and employees.

        In addition, SendGrid has agreed to specific restrictions relating to the conduct of its business between the date of the merger agreement and the effective time of the merger, including not to do any of the following (subject, in each case, to exceptions specified below and in the merger agreement or previously disclosed in writing to Twilio as provided in the merger agreement) without Twilio's prior written consent, which, subject to specified exceptions, may not be unreasonably withheld, conditioned or delayed:

    (i) Declare, set aside or pay any dividends on, or make any other distributions (whether in cash, stock, property or any combination thereof), in respect of, any of its capital stock, other equity

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      interests or voting securities, other than dividends and distributions by a direct or indirect wholly owned subsidiary to its parent; (ii) split, combine, subdivide or reclassify any of its capital stock, other equity interests or voting securities or securities convertible into or exchangeable or exercisable for capital stock or other equity interests or voting securities, or issue or authorize the issuance of any other securities in respect of, in lieu of or in substitution for, its capital stock, other equity interests or voting securities, or (iii) repurchase, redeem or otherwise acquire, or offer to repurchase, redeem or otherwise acquire, any capital stock or voting securities of, or equity interests in, SendGrid or any of its subsidiaries or any securities of SendGrid or any of its subsidiaries convertible into or exchangeable or exercisable for capital stock or voting securities of, or equity interests in, SendGrid or any of its subsidiaries, or any warrants, calls, options or other rights to acquire any such capital stock, securities or interests, other than (1) withholding of shares of SendGrid common stock to satisfy tax obligations with respect to awards granted under the existing SendGrid stock plans, (2) the acquisition by SendGrid of awards granted pursuant to the existing SendGrid stock plans in connection with the forfeiture of such awards and (3) the acquisition by SendGrid of shares of SendGrid common stock outstanding as of the date of the merger agreement pursuant to SendGrid's right (under written commitments in effect as of the date of the merger agreement) to acquire shares of SendGrid common stock held by any officer or other employee, or individual who is an independent contractor, consultant or director, of or to any of SendGrid or any of its subsidiaries upon termination of such person's employment or engagement by SendGrid or any of its subsidiaries;

    Issue, deliver, sell, grant, pledge or otherwise encumber or subject to any lien, other than liens permitted under the merger agreement, (except for transactions among SendGrid and its wholly owned subsidiaries) (A) any shares of capital stock of SendGrid or any of its subsidiaries, (B) any other equity interests or voting securities of SendGrid or any of its subsidiaries, (C) any securities convertible into or exchangeable or exercisable for capital stock or voting securities of, or other equity interests in, SendGrid or any of its subsidiaries, (D) any warrants, calls, options or other rights to acquire any capital stock or voting securities of, or other equity interests in, SendGrid or its subsidiaries, (E) any rights issued by SendGrid or any of its subsidiaries that are linked in any way to the price of any class of the capital stock of SendGrid or any shares of capital stock of any subsidiary of SendGrid, the value of SendGrid or any of its subsidiaries or any part of SendGrid or any of its subsidiaries or any dividends or other distributions declared or paid on any shares of capital stock of SendGrid or any of its subsidiaries, or (F) any bonds, debentures, notes or other indebtedness of SendGrid having the right to vote (or convertible into, or exchangeable for, securities having the right to vote) on any matters on which stockholders of SendGrid may vote except, in each case of (A) through (F), for issuing shares of SendGrid common stock in respect of SendGrid options, SendGrid restricted stock units or other equity awards outstanding under SendGrid's existing stock plans as of the date of the merger agreement;

    Amend its organizational documents (including by merger, consolidation or otherwise), or amend in any material respect the charter or organizational documents of any its subsidiaries (including by merger, consolidation or otherwise), except in each case as may be required by law;

    Except as required by applicable law, pursuant to the terms of any SendGrid benefit plan previously disclosed in writing to Twilio as provided in the merger agreement (or a comparable plan for the succeeding fiscal year) or any SendGrid material contract as in effect on the date of the merger agreement: (A) increase the salaries, bonus opportunities, incentive compensation or other compensation or benefits payable to any employee of SendGrid or any of its subsidiaries at a level of Vice President or higher, (B) increase the salaries, bonus opportunities, incentive compensation or other compensation or benefits payable to any employee with a title below director or other service provider of SendGrid or any of its subsidiaries; (C) grant, announce or

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      pay any new, retention, severance, change in control or other similar bonus or similar compensation to any employee of SendGrid or any of its subsidiaries, (D) establish, amend, terminate or increase the benefits or costs provided under any SendGrid benefit plan, (E) accelerate the vesting or payment of, or take any action to fund, any benefit or payment provided to employees or service providers of SendGrid or any of its subsidiaries, (F) hire, promote or terminate (without cause) any employee or service provider of SendGrid or any of its subsidiaries, in each case of this clause (F), other than in the ordinary course of business consistent with past practices for individuals at the level of senior director or lower, or (G) allow for the commencement of any new offering periods under the SendGrid employee stock purchase plan; provided that SendGrid and its subsidiaries (1) may change the title of their employees, provided such changes in title do not involve increases in the applicable employee's compensation or benefits, acceleration of vesting or acceleration of payment of the applicable employee's benefits or compensation; and (2) may make annual or quarterly cash bonus or commission payments, including cash bonus or commission payments pursuant to existing plans made available to Twilio as of the date of the merger agreement and cash payments to employees and set targets therefor in the ordinary course of business consistent with past practice;

    Make any material change in financial accounting methods, principles or practices, except as required by a change in GAAP (after the date of the merger agreement);

    Directly or indirectly acquire or agree to acquire in any transaction any equity interest in or business of any person (other than any transaction solely between SendGrid and one of its wholly owned subsidiaries or between wholly owned subsidiaries of SendGrid);

    Incur any indebtedness, except for (A) indebtedness incurred in the ordinary course of business consistent with past practice not to exceed $500,000 in the aggregate, (B) indebtedness in replacement of existing indebtedness, provided that the replacement indebtedness does not increase the aggregate amount of indebtedness permitted to be outstanding under the replaced indebtedness, (C) guarantees of indebtedness of any wholly owned subsidiary of SendGrid and guarantees by any subsidiary of SendGrid of indebtedness of SendGrid or any other wholly owned subsidiary of SendGrid, in each case, in the ordinary course of business consistent with past practice, (D) intercompany indebtedness among SendGrid and its wholly owned subsidiaries in the ordinary course of business consistent with past practice, (E) making borrowings under SendGrid's revolving credit facility (as existing on the date of the merger agreement) not to exceed $500,000, in the ordinary course of business consistent with past practice or (F) capital leases in the ordinary course of business not to exceed $1 million in the aggregate;

    Sell, lease (as lessor), license, covenant not to assert, mortgage, abandon, allow to lapse (other than any patent expiring at the end of its statutory term), and leaseback or otherwise encumber or subject to any lien (other than any lien permitted under the merger agreement), or otherwise dispose of any properties, rights or assets (including any intellectual property of SendGrid) that are material to SendGrid and its subsidiaries, taken as a whole (other than sales and non-exclusive licenses of products or services in the ordinary course of business consistent with past practice), except (A) pursuant to contracts or commitments in effect on the date of the merger agreement (or entered into after the date of the merger agreement without violating the terms of the merger agreement), (B) any of the foregoing with respect to inventory in the ordinary course of business consistent with past practice, (C) any of the foregoing with respect to obsolete or worthless equipment in the ordinary course of business consistent with past practice, (D) in relation to mortgages, liens and pledges to secure indebtedness for borrowed money permitted to be incurred under the merger agreement and guarantees thereof or (E) for any transactions among SendGrid and its wholly owned subsidiaries in the ordinary course of business consistent with past practice;

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    Make, or agree or commit to make, any capital expenditure not contemplated by SendGrid's capital plan for 2018 and 2019 in excess of $500,000 in the aggregate;

    Except as required by applicable law, make, change or revoke any material tax election, materially change any method of tax accounting or annual tax accounting period, settle any claim, action or proceeding relating to any material tax liability, agree to waive any statute of limitations for any material tax claim or assessment (other than pursuant to extensions of time to file tax returns obtained in the ordinary course of business), obtain or request any material tax ruling or closing agreement, or surrender any right to obtain a material tax refund;

    Enter any new line of business outside of SendGrid and its subsidiaries' existing business;

    Dissolve or liquidate SendGrid or any of its subsidiaries;

    Waive, release, assign, settle or compromise any claim, action or proceeding, other than waivers, releases, assignments, settlements or compromises (i) with respect to routine matters in the ordinary course of business or (ii) that do not create material obligations of SendGrid or any of its subsidiaries other than the payment of monetary damages (A) equal to or less than the amounts reserved with respect thereto on SendGrid's SEC documents or (B) not in excess of $500,000 in the aggregate;

    Except as required by applicable laws, enter into, modify, amend, extend, renew, replace or terminate any collective bargaining agreement or other labor union contract applicable to the employees of SendGrid or any of its subsidiaries, other than in the ordinary course of business consistent with past practice;

    Abandon, allow to lapse (other than any patent expiring at the end of its statutory term), subject to a lien (other than liens permitted under the merger agreement), assign, transfer, convey title (in whole or in part), license, covenant not to assert, grant any right or other licenses to, or otherwise dispose of, material trademarks, trademark rights, trade names or service marks or other material intellectual property of SendGrid, or enter into licenses or agreements that impose material restrictions upon SendGrid or any of its subsidiaries with respect to material trademarks, trademark rights, trade names or service marks or other material intellectual property rights owned by any third party, in each case other than non-exclusive licenses in the ordinary course of business consistent with past practice; or

    Other than in the ordinary course of business, materially amend or modify any material contract or enter into, materially amend or modify any contract that would be a material contract if it had been entered into prior to the date of the merger agreement, other than non-exclusive licenses in the ordinary course of business consistent with past practice; or

    Take any action that could reasonably be expected to prevent the merger from qualifying as a "reorganization" under Section 368(a) of the Code; or

    Change in any material respect any SendGrid data security or cybersecurity policy effective as of the date of the merger agreement; or

    Authorize any of, or commit, resolve or agree to take any of, the foregoing actions.

        In addition, Twilio has agreed to specific restrictions relating to the conduct of its business between the date of the merger agreement and the effective time of the merger, including not to do any of the following (subject, in each case, to exceptions specified below and in the merger agreement or previously disclosed in writing to SendGrid as provided in the merger agreement) without SendGrid's

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prior written consent, which, subject to specified exceptions, may not be unreasonably withheld, conditioned or delayed:

    Amend its charter or by-laws (other than any amendment to its by-laws that would not, and would not reasonably be expected to, (x) be materially and disproportionately adverse to the holders of shares of SendGrid common stock relative to the treatment of existing holders of Twilio Class A common stock or (y) change in any material respects the economic rights of Twilio Class A common stock);

    (A) Declare, set aside or pay any dividends on, or make any other distributions (whether in cash, stock, property or any combination thereof) in respect of, any of its capital stock, other equity interests or voting securities, other than dividends and distributions by a direct or indirect wholly owned subsidiary of Twilio to its parent, (B) split, combine, subdivide or reclassify any of its capital stock, other equity interests or voting securities, or securities convertible into or exchangeable or exercisable for capital stock or other equity interests or voting securities or issue or authorize the issuance of any other securities in respect of, in lieu of or in substitution for its capital stock, other equity interests or voting securities or (C) repurchase, redeem or otherwise acquire, or offer to repurchase, redeem or otherwise acquire, any capital stock or voting securities of, or equity interests in, Twilio or any of its subsidiaries or any securities of Twilio or any of its subsidiaries convertible into or exchangeable or exercisable for capital stock or voting securities of, or equity interests in, Twilio or any of its subsidiaries, or any warrants, calls, options or other rights to acquire any such capital stock, securities or interests, other than (1) the withholding of shares of Twilio Class A common stock to satisfy tax obligations with respect to awards granted pursuant to Twilio's stock plans, (2) the acquisition by Twilio of awards granted pursuant to Twilio's stock plans in connection with the forfeiture of such awards and (3) the acquisition by Twilio of shares of its Class A common stock outstanding as of the date of the merger agreement pursuant to its right (under written commitments in effect as of the date of the merger agreement) to acquire such shares held by any officer or other employee, or individual who is an independent contractor, consultant or director, of or to any of Twilio or any of its subsidiaries upon termination of such person's employment or engagement by Twilio or any of its subsidiaries;

    Issue, deliver, sell, grant, pledge or otherwise encumber or subject to any lien, other than liens permitted under the merger agreement, (except for transactions among Twilio and its wholly owned subsidiaries or transactions pursuant to contracts in effect as of the date of the merger agreement) (A) any shares of capital stock of Twilio or any of its subsidiaries, (B) any other equity interests or voting securities of Twilio or any of its subsidiaries, (C) any securities convertible into or exchangeable or exercisable for capital stock or voting securities of, or other equity interests in, Twilio or any of its subsidiaries, (D) any warrants, calls, options or other rights to acquire any capital stock or voting securities of, or other equity interests in, Twilio or any of its subsidiaries, (E) any rights issued by Twilio or any of its subsidiaries that are linked in any way to the price of any class of the capital stock of Twilio or any shares of capital stock of any of Twilio's subsidiaries, the value of Twilio, any of its subsidiaries or any part of Twilio or any of its subsidiaries or any dividends or other distributions declared or paid on any shares of capital stock of Twilio or any of its subsidiaries, or (F) any bonds, debentures, notes or other indebtedness of Twilio having the right to vote (or convertible into, or exchangeable for, securities having the right to vote) on any matters on which stockholders of Twilio may vote except, in each case of (A)-(F), for issuing shares of Twilio Class A common stock in respect of equity awards outstanding under Twilio's stock plans as of the date of the merger agreement and except that Twilio may issue Twilio stock options and Twilio restricted stock units in the ordinary course of business consistent with past practice;

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    Acquire another business or merge or consolidate with any other person or enter into any binding share exchange, business combination or similar transaction with another person or restructure, reorganize or completely or partially liquidate, in each case, to the extent that such action would, or would reasonably be expected to, (A) require the financial statements of such acquired person or business to be incorporated within Form S-4 under Regulation S-X of the Securities Act, (B) impose any delay in the expiration or termination of any applicable waiting period or impose any delay in the obtaining of, or increase the risk of not obtaining, any authorization, consent, clearance, approval or order of a governmental entity necessary to consummate the merger and the other transactions contemplated by the merger agreement, including any approvals and expiration of waiting periods pursuant to applicable antitrust laws, (C) increase the risk of any governmental entity entering, or increase the risk of not being able to remove or successfully challenge, any permanent, preliminary or temporary injunction or other order, decree, decision, determination or judgment that would delay, restrain, prevent, enjoin or otherwise prohibit consummation of the merger and the other transactions contemplated by the merger agreement or (D) otherwise prevent, materially delay or materially impair the consummation of the merger;

    Except insofar as may have been required by a change in GAAP (after the date of the merger agreement), make any material change in financial accounting methods, principles or practices if such change (A) would reasonably be expected to result in a delay in the filing of Form S-4 with the SEC and (B) would otherwise reasonably be expected to prevent, materially delay or materially impair the consummation of the merger;

    Take any action that could reasonably be expected to prevent the merger from qualifying as a "reorganization" under Section 368(a) of the Code; or

    Agree, resolve or commit to do any of the foregoing.

No Solicitation of Alternative Proposals

        Each of SendGrid and Twilio has agreed that, from the time of the execution of the merger agreement until the earlier of the termination of the merger agreement or the consummation of the merger, it and its subsidiaries will not, and it will cause its and its subsidiaries' directors, officers and employees not to, and will use reasonable best efforts to cause its and their respective investment bankers, attorneys, accountants and other advisors, agents or representatives (collectively, along with such directors, officers and employees, "representatives") not to, directly or indirectly, (i) solicit, initiate, knowingly induce, knowingly encourage or knowingly facilitate (including by way of furnishing information) any inquiries or the making of any proposal or offer that constitutes an acquisition proposal or that would reasonably be expected to lead to an acquisition proposal, (ii) participate in any negotiations or discussions or cooperate in any way (except as otherwise permitted under the terms of the merger agreement) with any person regarding any proposal the consummation of which would constitute an acquisition proposal, (iii) provide any information or data concerning itself or any of its subsidiaries to any person in connection with any proposal that, if consummated, would constitute an acquisition proposal or (iv) approve, recommend, make any public statement approving or recommending, or enter into any agreement with respect to any inquiry, proposal or offer that constitutes an acquisition proposal or that would reasonably be expected to lead to an acquisition proposal.

        The merger agreement also requires both Twilio and SendGrid to, and to cause each of its respective subsidiaries and representatives to, immediately cease and cause to be terminated any and all existing activities, discussions or negotiations with any parties conducted prior to the execution of the merger agreement with respect to any acquisition proposal or proposal that would reasonably be expected to lead to an acquisition proposal.

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        An "acquisition proposal" with respect to SendGrid means any proposal (other than an offer or proposal made by Twilio or any of its subsidiaries) for (i) any merger, consolidation, share exchange, business combination, issuance of securities, direct or indirect acquisition of securities, recapitalization, tender offer, exchange offer or other similar transaction in which (x) a person or "group" (as defined in the Exchange Act and the rules promulgated thereunder) of persons directly or indirectly acquires, or if consummated in accordance with its terms would acquire, beneficial or record ownership of securities representing more than 20% of the outstanding shares of any class of voting securities of SendGrid; or (y) SendGrid issues securities representing more than 20% of the outstanding shares of any class of voting securities of SendGrid; (ii) any direct or indirect sale, lease, exchange, transfer, acquisition or disposition of any assets of SendGrid and of its subsidiaries that constitute or account for (x) more than 20% of the consolidated net revenues, consolidated net income or consolidated book value of SendGrid; or (y) more than 20% of the fair market value of the assets of SendGrid; or (iii) any liquidation or dissolution of SendGrid.

        An "acquisition proposal" with respect to Twilio means any proposal (other than an offer or proposal made by SendGrid or any of its subsidiaries) for (i) any merger, consolidation, share exchange, business combination, issuance of securities, direct or indirect acquisition of securities, recapitalization, tender offer, exchange offer or other similar transaction in which (x) a person or "group"(as defined in the Exchange Act and the rules promulgated thereunder) of persons directly or indirectly acquires, or if consummated in accordance with its terms would acquire, beneficial or record ownership of securities representing more than 20% of the outstanding shares of any class of voting securities of Twilio; or (y) Twilio issues securities representing more than 20% of the outstanding shares of any class of voting securities of Twilio; (ii) any direct or indirect sale, lease, exchange, transfer, acquisition or disposition of any assets of Twilio and its subsidiaries that constitute or account for (x) more than 20% of the consolidated net revenues, consolidated net income or consolidated book value of Twilio; or (y) more than 20% of the fair market value of the assets of Twilio; or (iii) any liquidation or dissolution of Twilio.

        Notwithstanding the restrictions described above, if, prior to obtaining SendGrid stockholder approval, SendGrid receives an unsolicited, written acquisition proposal that did not result from a breach, in any material respect, of the merger agreement from a third party, then SendGrid may (i) contact the third party making such acquisition proposal to clarify the terms and conditions thereof and inform them of the terms of the merger agreement applicable to such acquisition proposal, (ii) provide access to non-public information regarding SendGrid and its subsidiaries to such third party; provided that such information has previously been available to Twilio or is provided to Twilio substantially concurrently with the making of such information available to such third party and that, prior to furnishing any such material non-public information, SendGrid receives from such third party an executed confidentiality agreement with terms at least as restrictive in all material respects on such third party as the terms of the confidentiality agreement between SendGrid and Twilio are on Twilio (it being understood that such confidentiality agreement need not prohibit the making or amending of the acquisition proposal) and (iii) participate or engage in any negotiations or discussions with such third party if, and only if, prior to taking any action described in clause (ii) or (iii) above, the SendGrid Board determines in good faith after consultation with outside legal counsel that (A) based on the information then available and after consultation with a financial advisor of nationally recognized reputation that such acquisition proposal constitutes, or could reasonably be expected to result in, a superior proposal and (B) the failure to take such action would reasonably be expected to be inconsistent with the directors' fiduciary duties under applicable law.

        Notwithstanding the restrictions described above, if, prior to obtaining Twilio stockholder approval, Twilio receives an unsolicited, written acquisition proposal from a third party that did not result from a breach, in any material respect, of the merger agreement, then Twilio may (i) contact the third party making such acquisition proposal to clarify the terms and conditions thereof and information them of the terms of the merger agreement applicable to such acquisition proposal, (ii) provide access to

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non-public information regarding Twilio and its subsidiaries to such third party; provided that such information has previously been made available to SendGrid or is provided to SendGrid substantially concurrently with the making of such information available to such third party and that, prior to furnishing any such material non-public information, Twilio receives from the third party making such acquisition proposal an executed confidentiality agreement with terms at least as restrictive in all material respects on such third party as the terms of the confidentiality agreement between SendGrid and Twilio are on SendGrid (it being understood that such confidentiality agreement need not prohibit the making or amending of the acquisition proposal) and (iii) participate or engage in any negotiations or discussions with such third party if, and only if, prior to taking such actions, the Twilio Board determines in good faith after consultation with outside legal counsel that (A) based on the information then available and after consultation with a financial advisor of nationally recognized reputation that such acquisition proposal constitutes, or could reasonably be expected to result in, a superior proposal and (B) the failure to take such action would reasonably be expected to be inconsistent with the directors' fiduciary duties under applicable law.

        A "superior proposal" means any bona fide, binding, written acquisition proposal (with all percentages in the applicable definition of acquisition proposal above increased to 80%) on terms which the SendGrid Board or the Twilio Board, as the case may be, determines in its good faith judgment (after consultation with outside legal counsel and a financial advisor of nationally recognized reputation) would reasonably be expected to be consummated in accordance with its terms (taking into account all legal, financial and regulatory aspects of the proposal and the party making the proposal) and, if consummated, would result in a transaction more favorable to the SendGrid stockholders or Twilio stockholders, as the case may be, from a financial point of view than the merger (including any changes to the terms of the merger agreement made in response to such offer in accordance with the merger agreement) and the time likely required to consummate the applicable acquisition proposal.

        The merger agreement requires each party to notify the other promptly (and, in any event, within one business day) of, among other things, the receipt of any written or other inquiries, proposals or offers that is or could reasonably be expected to lead to an acquisition proposal, any non-public information requested in connection with such an acquisition proposal or any discussion or negotiation with respect to or that could reasonably be expected to lead to an acquisition proposal (indicating, in such notice, the identity of the potential counterparty and the material terms and conditions of any such proposal or offer, including proposed agreements and other material written communications). In addition, the merger agreement requires each party to continue to inform the other of the status of any such proposals or offers and the status of any such discussion or negotiations.

Changes in Board Recommendations

        Each of Twilio and SendGrid has agreed that its board of directors and each committee of its board of directions shall not (i) withhold, withdraw, qualify or modify (or publicly propose or resolve to withhold, withdraw, qualify or modify), in any manner adverse to the other party, the recommendation by such board with respect to the transactions contemplated by the merger agreement, as applicable, or approve, recommend or otherwise declare advisable (or publicly propose or resolve to approve, recommend or otherwise declare advisable) any applicable acquisition proposal or make or authorize the making of any public statement (oral or written) that has the substantive effect of such a withdrawal, qualification or modification (each such event, a "change in recommendation"), (ii) cause Twilio or SendGrid, as the case may be, or any of its respective subsidiaries, to enter into any agreement relating to any acquisition proposal or requiring such party (or that would require such party) to abandon, terminate, or fail to consummate the merger or any other transaction contemplated by the merger agreement (an "alternative acquisition agreement").

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        Notwithstanding the foregoing, each of the Twilio Board and the SendGrid Board may change its recommendation to its respective stockholders (subject to the other party's rights to match competing proposals and right to terminate the merger agreement following such change in recommendation, as more fully described in the merger agreement) in response to a superior proposal or an intervening event if the Twilio Board or the SendGrid Board, as applicable determines in good faith, after consultation with financial advisors of nationally recognized reputation and outside legal counsel, that the failure to take such action would be inconsistent with the applicable directors' fiduciary duties under applicable law.

        An "intervening event" with respect to Twilio means any event, occurrence, fact, condition, change, development or effect that (i) was not known to, or reasonably foreseeable by the Twilio Board prior to the execution of the merger agreement, which event, occurrence, fact, condition, change, development or effect becomes known to, or reasonably foreseeable by, the Twilio Board prior to the receipt of the Twilio stockholder approval and (ii) does not relate to (A) any changes in the market price or trading volume of Twilio or SendGrid, (B) Twilio or SendGrid meeting, failing to meet or exceeding published or unpublished revenue or earnings projections, in each case in and of itself (it being understood that with respect to each of clause (A) and clause (B) the facts or occurrences giving rise or contributing to such change or event may be taken into account when determining an intervening event with respect to Twilio to the extent otherwise satisfying this definition), or (C) an acquisition proposal with respect to Twilio.

        An "intervening event" with respect to SendGrid means any event, occurrence, fact, condition, change, development or effect that (i) was not known to, or reasonably foreseeable by, the SendGrid Board prior to the execution of the merger agreement, which event, occurrence, fact, condition, change, development or effect becomes known to, or reasonably foreseeable by, the SendGrid Board prior to the receipt of the SendGrid stockholder approval and (ii) does not relate to (A) an acquisition proposal or (B) (1) any changes in the market price or trading volume of Twilio or SendGrid or (2) Twilio or SendGrid meeting, failing to meet or exceeding published or unpublished revenue or earnings projections, in each case in and of itself (it being understood that with respect to each of clause (1) and clause (2) the facts or occurrences giving rise or contributing to such change or event may be taken into account when determining an intervening event with respect to SendGrid to the extent otherwise satisfying this definition).

Efforts to Obtain Required Stockholder Votes

        SendGrid has agreed, subject to the qualifications described above, to use its reasonable best efforts to convene and hold a meeting of its stockholders to consider and vote upon the adoption of the merger agreement and the advisory (non-binding) vote to approve the SendGrid compensation proposal within forty-five days after the declaration of the effectiveness of the Form S-4 of which this joint proxy statement/prospectus forms a part. The SendGrid Board has approved the merger agreement and determined the merger agreement and the transactions contemplated thereby, including the merger, are advisable, fair to and in the best interests of SendGrid and its stockholders, and has adopted resolutions directing that the merger agreement be submitted to the SendGrid stockholders for their consideration. Notwithstanding the foregoing, (x) if on or before the date the SendGrid stockholders meeting is scheduled to be held, SendGrid reasonably believes that (A) it will not receive proxies representing a sufficient number of shares of SendGrid common stock to adopt the merger agreement and the transactions contemplated thereby or (B) it will not have enough shares of SendGrid common stock to constitute a quorum, SendGrid has the right to (and, if requested by Twilio, must) on one or more occasions postpone or adjourn the SendGrid stockholders meeting and (y) SendGrid may postpone or adjourn the SendGrid stockholders meeting to allow reasonable additional time for the filing or mailing of any supplemental or amended disclosure that SendGrid has determined, after consultation with outside legal counsel, is reasonably likely to be required under

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applicable law and for such supplemental or amended disclosure to be disseminated and reviewed by SendGrid stockholders prior to the SendGrid special meeting, as long as the SendGrid special meeting is not adjourned or postponed for more than an aggregate of 15 calendar days in connection with any such postponements or adjournments pursuant to either or both of the preceding clauses (x) and (y).

        Notwithstanding any SendGrid change in recommendation, SendGrid shall submit the merger agreement to its stockholders for adoption at the SendGrid stockholders meeting unless the merger agreement is terminated in accordance with its terms prior to such meeting. Without the prior written consent of Twilio, the adoption of the merger agreement shall be the only matter (other than matters of procedure and matters required by law to be voted on by SendGrid's stockholders in connection with the adoption of the merger agreement and the transactions contemplated thereby) that SendGrid shall propose to be acted on by its stockholders at the SendGrid stockholders meeting.

        Twilio has agreed, subject to the qualifications described above, to use its reasonable best efforts to convene and hold a meeting of its stockholders to consider and vote upon the issuance of the Twilio Class A common stock to be issued to SendGrid stockholders in connection with the merger within forty-five days after the declaration of the effectiveness of the Form S-4 of which this joint proxy statement/prospectus forms a part. The Twilio Board has approved the merger agreement and determined the merger agreement and the transactions contemplated thereby, including the issuance of Twilio Class A common stock to SendGrid stockholders in connection with the merger, are advisable, fair to and in the best interests of Twilio and its stockholders, and has adopted resolutions directing that the Twilio stock issuance proposal be submitted to the Twilio stockholders for their consideration. Notwithstanding the foregoing, (x) if on or before the date the Twilio stockholders meeting is scheduled to be held, Twilio reasonably believes that (A) it will not receive proxies representing a sufficient number of shares of Twilio Class A common stock and Twilio Class B common stock to approve the Twilio stock issuance proposal or (B) it will not have enough shares of Twilio Class A common stock and Twilio Class B common stock to constitute a quorum, Twilio has the right to (and, if requested by SendGrid, must) on one or more occasions postpone or adjourn the Twilio stockholders and (y) Twilio may postpone or adjourn the Twilio stockholders meeting to allow reasonable additional time for the filing or mailing of any supplemental or amended disclosure that Twilio has determined, after consultation with outside legal counsel, is reasonably likely to be required under applicable law and for such supplemental or amended disclosure to be disseminated and reviewed by Twilio stockholders prior to the Twilio special meeting, as long as the Twilio special meeting is not adjourned or postponed for more than an aggregate of 15 calendar days in connection with any such postponements or adjournments pursuant to either or both of the preceding clauses (x) and (y).

        Notwithstanding the foregoing, Twilio shall (i) cause the independent directors and executive officers of Twilio appointed as attorney and proxy in each proxy delivered concurrently with the execution and delivery of the merger agreement (the "Twilio proxies") to vote the shares of Twilio Class B common stock at the Twilio stockholders meeting to approve the issuance of shares of Twilio Class A common stock pursuant to the merger agreement and to otherwise vote the shares of such Twilio Class B common stock in accordance with the Twilio proxies at the Twilio stockholders meeting, (ii) take all other actions necessary or advisable to effectuate the intent of the Twilio proxies, including designating any additional officers or directors of Twilio to act as substitute attorneys and proxies under the Twilio proxies in the event that any of the directors or officers listed therein are unwilling or unable to vote the shares of Twilio Class B common stock in accordance with the Twilio proxies at the Twilio stockholders meeting and (iii) shall take all actions necessary or advisable to prevent such Twilio proxies from being revoked (to the maximum extent permitted under applicable laws).

        Notwithstanding any Twilio change in recommendation, Twilio shall seek the Twilio stockholder approval at the Twilio stockholders meeting unless the merger agreement is terminated in accordance with its terms prior to such meeting. Without the prior written consent of SendGrid, the Twilio stock issuance shall be the only matter (other than matters of procedure and matters required by law to be

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voted on by Twilio's stockholders in connection with the transactions contemplated by the merger agreement) that Twilio shall propose to be acted on by its stockholders at the Twilio stockholders meeting.

Efforts to Complete the Merger

        Twilio and SendGrid have each agreed to cooperate with each other and use, and to cause their respective subsidiaries to use, their respective reasonable best efforts to take or cause to be taken all actions, and do or cause to be done all things, necessary, proper or advisable under the merger agreement and applicable laws to consummate and make effective the merger and the other transactions contemplated by the merger agreement as expeditiously as possible, including preparing and filing all documentation to effect all necessary notices, reports and other filings (and in any event, by filing within 10 business days after the date of the merger agreement the notifications, filings and other information required to be filed under the HSR Act and to obtain as expeditiously as possible all consents, expirations of waiting periods and authorizations necessary or advisable to be obtained from any third party and/or any governmental entity pursuant to the HSR Act in order to consummate the merger or any of the other transactions contemplated by the merger agreement, (ii) satisfying the conditions to consummating the merger, (iii) defending any lawsuits or other legal proceedings, whether judicial or administrative, challenging the merger agreement or the consummation of the merger, (iv) using commercially reasonable efforts to obtain (and cooperating with each other in obtaining) any consent, approval of, waiver or any exemption by, any non-governmental third party, in each case, to the extent necessary, proper or advisable in connection with the merger and (v) executing and delivering any reasonable additional instruments necessary to consummate the transactions contemplated hereby and to fully carry out the purposes of the merger agreement.

SendGrid Employee Benefits Matters

        From the effective time of the merger until the first anniversary of the closing of the merger (the "continuation period"), Twilio will provide each employee of SendGrid who continues to remain employed by SendGrid, Twilio or the surviving company following the effective time of the merger, which we refer to as a continuing employee, with (i) an annual rate of base salary or base wage that is no less favorable than the base salary or base wage that was provided to such continuing employee immediately prior to the effective time of the merger, and (ii) other benefits (excluding equity-based compensation, cash incentive arrangements and any pension, post-retirement or deferred compensation benefits) that are substantially comparable in the aggregate to those that were provided to such continuing employee immediately prior to the effective time of the merger.

        To the extent continuing employees become eligible to participate in any employee benefit plan maintained by Twilio or its subsidiaries following the effective time of the merger, the continuing employees' service with SendGrid or any of its subsidiaries as of the effective time of the merger will be treated as service with Twilio or its subsidiaries for purposes of eligibility, vesting (excluding for any equity-based compensation), vacation, paid time off and severance entitlements to the same extent and for the same purposes as such service was credited under SendGrid's benefit plans, provided that such service will not be recognized to the extent that such recognition would result in a duplication of benefits. Twilio will use commercially reasonable efforts to waive eligibility requirements and pre-existing condition limitations under any Twilio benefit plan, to the extent permitted by such plans and except to the extent such eligibility requirements or pre-existing conditions would apply under the analogous SendGrid benefit plan in which the continuing employee participated or was eligible to participate prior to the effective time of the merger. In addition, with respect to the plan year during which the effective time of the merger occurs, Twilio will use commercially reasonable efforts to give credit, in determining any deductibles or out-of-pocket limitations under any Twilio benefit plan, to

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amounts paid by continuing employees prior to the closing of the merger under any SendGrid benefit plan, to the extent permitted by such plans.

        If Twilio requests, at least 10 business days prior to the effective time of the merger, SendGrid will take any and all actions required to amend, suspend or terminate SendGrid's 401(k) plan immediately prior to the effective time of the merger to the extent such actions are permitted by law (including any required prior notice obligations), by the terms of the merger agreement and the terms of such 401(k) plan; provided that any amendment, suspension or termination of such 401(k) plan will not impact the benefits required to be provided to continuing employees during the continuation period as described above. Twilio will (i) allow eligible rollover contributions to Twilio's 401(k) plan of the continuing employees' account balances (in cash) and (ii) use reasonable best efforts to accommodate eligible rollover contributions to Twilio's 401(k) plan of the continuing employees' account balances in loan notes evidencing loans to continuing employees as of the date of distribution, in each case from SendGrid's 401(k) plan as soon as practicable following the closing date.

Indemnification and Insurance

        The merger agreement requires Twilio to indemnify, to the fullest extent permitted by law, any person who is now an officer or director of SendGrid or has been at any time prior to the effective time of the merger an officer or director of SendGrid, in connection with any claim, action, suit, proceeding or investigation arising out of acts or omissions occurring or alleged to have occurred at or prior to the effective time of the merger in connection with the fact that such person was an officer or director of SendGrid, or is or was serving at the request of SendGrid as an officer or director of another entity.

        Twilio shall also ensure that the organizational documents of the surviving company will contain provisions no less favorable with respect to the indemnification, advancement of expenses and exculpation of present and former directors and officers of SendGrid than those presently contained in SendGrid's organizational documents.

        The merger agreement requires Twilio to cause the surviving company to purchase a six-year "tail" prepaid officers' and directors' liability insurance policy prior to the effective time of the merger with benefits and levels of coverage at least as favorable as SendGrid's existing policies with respect to matters existing or occurring at or prior to the effective time of the merger for an amount not to exceed 300% of SendGrid's current annual premiums.

Treatment of SendGrid Equity Awards

        Treatment of Restricted Stock Unit Awards.    At the effective time of the merger, each 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 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 SendGrid option that is outstanding and unexercised immediately prior to such time, whether vested or unvested (other than (i) any SendGrid option held by a former employee or former service provider of SendGrid, or a subsidiary of SendGrid and (ii) any SendGrid UK option) will be assumed by Twilio and converted into

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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 UK 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).

        Treatment of ESPP.    Following the date of the merger agreement, SendGrid has taken actions with respect to the ESPP to provide that with respect to 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.

Other Covenants and Agreements

        The merger agreement contains certain other covenants and agreements, including covenants relating to:

    Twilio using reasonable best efforts to cause the shares of Twilio Class A common stock to be issued in the merger to be approved for listing on the NYSE, subject to official notice of issuance, prior to the effective time of the merger;

    SendGrid taking all actions necessary to permit the shares of SendGrid common stock and any other security issued by SendGrid or one of its subsidiaries and listed on the NYSE to be de-listed from the NYSE and de-registered under the Exchange Act as soon as possible following the effective time of the merger;

    both Twilio and SendGrid and their respective boards using reasonable best efforts to take all action reasonably appropriate to ensure that no state takeover statute or similar statute or regulation is or becomes applicable to the merger agreement or the transactions contemplated thereunder, including the merger, and, if any state takeover statute or similar statute or regulation becomes applicable to the merger agreement or the transactions contemplated thereunder, including the merger, taking all action reasonably appropriate to ensure that the

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      transactions contemplated by the merger agreement, including the merger, may be consummated as promptly as practicable on the terms contemplated by the merger agreement;

    both Twilio and SendGrid keeping the other party reasonably apprised of the status of matters relating to completion of the transactions contemplated under the merger agreement, including promptly furnishing the other with copies of notice or other communications from any third party and/or any governmental entity with respect to the merger and the other transactions contemplated by the merger agreement, other than immaterial communications;

    both Twilio and SendGrid providing prompt notification to the other party of any litigation related to the merger that is brought or threatened against such party or its directors or officers and keeping the other party informed on a reasonably current basis with respect to the status thereof. The parties agree to cooperate in the defense and settlement of any such litigation, and neither party shall settle any such litigation without the prior written consent of the other party (not to be unreasonably withheld, conditioned or delayed).

    use of reasonable best efforts to cause the merger to qualify as a "reorganization" within the meaning of Section 368(a) of the Code, deliver the representations of its officers required in connection with the issuance of the opinions of counsel that the merger will be treated as a "reorganization" within the meaning of Section 368(a) of the Code and obtain such opinions in connection therewith. Unless otherwise required pursuant to a "determination" within the meaning of Section 1313(a) of the Code, the parties also will report the merger for U.S. federal income tax purposes as a "reorganization" within the meaning of Section 368(a) of the Code in all tax returns and will not take any tax reporting position inconsistent with such characterization.

Conditions to Completion of the Merger

        The obligations of each of Twilio and SendGrid to effect the merger are subject to the satisfaction, or waiver, of the following conditions:

    Approval of the merger agreement by holders of a majority of the outstanding shares of SendGrid common stock entitled to vote thereon at the SendGrid stockholders meeting.

    Approval of the Twilio stock issuance by the affirmative vote of a majority of the outstanding shares of Twilio Class A common stock and Twilio Class B common stock entitled to vote thereon and present in person or represented by proxy at the Twilio stockholders meeting, voting together as a single class.

    Expiration or earlier termination of all waiting periods applicable to the merger under the HSR Act. SendGrid and Twilio received notification of early termination of the waiting period under the HSR Act on November 20, 2018.

    No governmental entity of competent jurisdiction shall have issued, enacted, promulgated, enforced or entered any law or judgment (whether temporary, preliminary or permanent) that is in effect and restrains, enjoins or otherwise prohibits consummation of the merger.

    Shares of Twilio Class A common stock issuable to SendGrid's stockholders pursuant to the merger agreement shall have been approved for listing on the NYSE, subject to official notice of issuance.

    The Form S-4 registration statement of which this joint proxy statement/prospectus forms a part has been declared effective by the SEC under the Securities Act and no stop order suspending the effectiveness of such Form S-4 has been issued and no proceedings for that purpose have been initiated or threatened.

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        In addition, the obligations of Twilio and Merger Sub to effect the merger are subject to the satisfaction, or waiver, of the following additional conditions:

    The representations and warranties of SendGrid contained in the merger agreement (except for the representations and warranties relating to (i) organization, good standing and qualification, (ii) certain capitalization and related matters, (iii) corporate authority and approval and (iv) brokers and finders) being true and correct as of the date of the merger agreement and as of the effective date of the merger as if made at and as of such time (other than those representations and warranties that were made only as of an earlier date, which need only be true and correct as of that date) except where the failure of such representations and warranties to be true and correct (without giving effect to any limitation as to materiality or material adverse effect set forth in such representations and warranties) individually or in the aggregate, has not had and would not reasonably be expected to have a material adverse effect with respect to SendGrid;

    The representations and warranties of SendGrid relating to (i) organization, good standing and qualification, (ii) corporate authority and approval and (iii) brokers and finders, being true and correct in all material respects at and as of the date of the merger agreement and as of the effective date of the merger as if made at and as of such time (other than those representations and warranties that were made only as of an earlier date, which need only be true and correct as of that date);

    The representations and warranties of SendGrid relating to certain capitalization and related matters shall be true and correct in all respects at and as of the date of the merger agreement and at and as of the effective date of the merger as if made at and as of such time (except to the extent expressly made as of an earlier date, in which case as of such earlier date), except to the extent the failures of such representations and warranties to be true and correct individually and in the aggregate would not result in an increase in the aggregate value of the consideration payable by Twilio in connection with the merger of more than $7.5 million, in the aggregate (valuing any shares, options or other awards that Twilio is required to issue or make in connection therewith pursuant to the terms of the merger agreement at a price equal to the closing price of a share of Twilio Class A common stock as reported on the NYSE on the business day immediately prior to the effective time of the merger), as compared to what such aggregate amount would have been if such representations and warranties had been true and correct in all respects;

    SendGrid having in all material respects performed all obligations required to be performed by it under the merger agreement at or prior to the effective time of the merger;

    No fact, circumstance, effect, change, event or development occurring after the date of the merger agreement that, individually or in the aggregate, has resulted, or would reasonably be likely to result, in a material adverse effect on SendGrid;

    Twilio's receipt of the tax opinion of Goodwin Procter LLP (or if Goodwin Procter LLP is unable to issue such opinion, of another nationally recognized law firm proposed by SendGrid that is reasonably acceptable 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; and

    Twilio's receipt of a certificate, dated as of the closing date of the merger, from a SendGrid senior executive officer, confirming that the conditions in the previous six bullet points above have been satisfied.

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        In addition, the obligations of SendGrid to effect the merger are subject to the satisfaction, or waiver, of the following additional conditions:

    The representations and warranties of Twilio contained in the merger agreement (except for the representations and warranties relating to (i) organization, good standing and qualification, (ii) certain capitalization and related matters, (iii) corporate authority and approval and (iv) brokers and finders) being true and correct as of the date of the merger agreement and as of the effective date of the merger as if made at and as of such time (other than those representations and warranties that were made only as of an earlier date, which need only be true and correct as of that date) except where the failure of such representations and warranties to be true and correct individually or in the aggregate, has not had and would not reasonably be expected to have a material adverse effect;

    The representations and warranties of Twilio relating to (i) organization, good standing and qualification, (ii) corporate authority and approval and (iii) brokers and finders, being true and correct in all material respects at and as of the date of the date of the merger agreement and as of the effective date of the merger as if made at and as of such time (other than those representations and warranties that were made only as of an earlier date, which need only be true and correct as of that date);

    The representations and warranties of Twilio relating to certain capitalization and related matters shall be true and correct in all respects, at and as of the date of the merger agreement and at and as of the effective date of the merger as if made at and as of such time (except to the extent expressly made as of an earlier date, in which case as of such earlier date) except to the extent the failures of such representations and warranties to be true and correct individually and in the aggregate would not result in an increase in the fully diluted capitalization of Twilio as of the date specified in Section 4.2 of the merger agreement (calculated using the treasury stock method for equity awards) by more than $35 million, in the aggregate (valuing any shares, options or other awards of Twilio that are outstanding at a price equal to the closing price of a share of Twilio Class A common stock as reported on the NYSE on the business bay immediately prior to the closing date of the merger) as compared to what such fully diluted capitalization would have been if such representations and warranties had been true and correct in all respects;

    Each of Twilio and Merger Sub having performed in all material respects all obligations required to be performed by it under the merger agreement at or prior to the effective time of the merger;

    No fact, circumstance, effect, change, event or development occurring after the date of the merger agreement that, individually or in the aggregate, has resulted, or would reasonably be likely to result, in a material adverse effect on Twilio;

    SendGrid's receipt of the tax opinion of Cooley LLP (or if Cooley LLP is unable to issue such opinion, of another nationally recognized law firm proposed by Twilio that is reasonably acceptable 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

    SendGrid's receipt of a certificate, dated as of the closing date of the merger, from a Twilio senior executive officer, confirming that the conditions in the previous six bullet points above have been satisfied.

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Termination of the Merger Agreement

        The merger agreement may be terminated and the merger abandoned at any time prior to the effective time of the merger, and, except as described below, under the following circumstances:

    by mutual written consent of Twilio and SendGrid, whether before or after the receipt of the required stockholder approvals;

    by either Twilio or SendGrid if the merger is not consummated by 11:59 p.m. New York City time on July 15, 2019, provided that such right to terminate the merger agreement shall not be available to any party that has breached in any material respect its obligations under the merger agreement in any manner that shall have been the primary cause of, or resulted in, the failure of the merger to be consummated by such time and date;

    by either Twilio or SendGrid if any law or judgment permanently restraining, enjoining or otherwise prohibiting consummation of the merger shall become final and non-appealable, whether before or after the date of the Twilio stockholder approval or the SendGrid stockholder approval, provided that such right to terminate the merger agreement shall not be available to any party that has breached in any material respect its obligations under the merger agreement in any manner that shall have been the primary cause of the failure of the merger to be consummated;

    by either Twilio or SendGrid if the SendGrid stockholder approval shall not have been obtained at a meeting duly convened therefor or at any adjournment or postponement thereof at which a vote upon the adoption of the merger agreement was taken, provided that such right to terminate the merger agreement shall not be available to any party that has breached in any material respect its obligations under the merger agreement in any manner that shall have been the primary cause of the failure of SendGrid to obtain the SendGrid stockholder approval; or

    by either Twilio or SendGrid if the Twilio stockholder approval shall not shall not have been obtained at a meeting duly convened therefor or at any adjournment or postponement thereof at which a vote upon the issuance of the Twilio Class A common stock was taken, provided that such right to terminate the merger agreement shall not be available to any party that has breached in any material respect its obligations under the merger agreement in any manner that shall have been the primary cause of the failure of Twilio to obtain the Twilio stockholder approval.

        The merger agreement may be terminated and the merger abandoned at any time before the effective time of the merger by SendGrid:

    If, prior to the time the Twilio stockholder approval is obtained, (i) the Twilio Board effects a change in recommendation, (ii) Twilio fails to include the Twilio Board recommendation in this joint proxy statement/prospectus or (iii) Twilio materially breaches or fails to perform its non-solicitation obligations pursuant to the merger agreement, which we refer to as a Twilio triggering event;

    If, at any time prior to the effective time of the merger, whether before or after the SendGrid stockholder approval is obtained, by action of the SendGrid Board if there has been a breach of any representation, warranty, covenant or agreement made by Twilio or Merger Sub in the merger agreement, or any such representation and warranty shall have become untrue after the date of the merger agreement, such that the closing conditions set forth in the merger agreement related to breaches of representations and warranties and performance of obligations would not be satisfied and such breach or failure to be true is not curable or, if curable, is not cured prior to the earlier of (i) 30 days following notice to Twilio from SendGrid of such breach or failure and (ii) the date that is three business days prior to July 15, 2019; provided that

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      SendGrid shall not have the right to terminate the merger agreement pursuant to this provision if SendGrid is then in material breach of any of its representations, warranties, covenants or agreements under the merger agreement; or

    To enter into a superior proposal in accordance with the terms of the merger agreement at any time prior to the SendGrid stockholder approval being obtained.

        The merger agreement may be terminated and the merger abandoned at any time before the effective time of the merger by Twilio:

    If, prior to the time the SendGrid stockholder approval is obtained, (i) the SendGrid Board effects a change in recommendation, (ii) SendGrid fails to include the SendGrid Board recommendation in this joint proxy statement/prospectus or (iii) SendGrid materially breaches or fails to perform the non-solicitation provisions of the merger agreement, which we refer to as a SendGrid triggering event;

    If, at any time prior to the effective time of the merger, whether before or after the Twilio stockholder approval is obtained, by action of the Twilio Board, if there has been a breach of any representation, warranty, covenant or agreement made by SendGrid in the merger agreement, or any such representation and warranty shall have become untrue after the date of the merger agreement, such that the closing conditions set forth in the merger agreement related to breaches of representations and warranties and performance of obligations would not be satisfied and such breach or failure to be true is not curable or, if curable, is not cured prior to the earlier of (i) 30 days following notice to SendGrid from Twilio of such breach or failure and (ii) the date that is three business days prior to July 15, 2019; provided that Twilio shall not have the right to terminate the merger agreement pursuant to this provision if Twilio is then in material breach of any of its representations, warranties, covenants or agreements under the merger agreement; or

    To enter into a superior proposal in accordance with the terms of the merger agreement at any time prior to the Twilio stockholder approval being obtained.

Termination Fees and Expenses; Liability for Breach

        If the merger agreement is terminated (i) by Twilio following a SendGrid triggering event or (ii) by SendGrid to enter into a superior proposal, SendGrid shall pay Twilio a fee equal to $69 million within two business days after such termination in the case of clause (i) or concurrently with such termination in the case of clause (ii).

        Further, (i) the merger agreement is terminated by Twilio or SendGrid due to a failure to close the merger by the termination date or failure to obtain the SendGrid stockholder approval, (ii) prior to such termination referred to in clause (i) of this sentence, but after the date of the merger agreement, a bona fide acquisition proposal with respect to SendGrid shall have been publicly made to SendGrid or its stockholders and not publicly withdrawn, and (iii) within nine months after the date of a termination in either of the cases referred to in clause (i) of this sentence, SendGrid consummates an acquisition proposal with respect to SendGrid or enters into an agreement contemplating an acquisition proposal with respect to SendGrid that is subsequently consummated, then SendGrid will pay Twilio a fee equal to $69 million, less any expenses of Twilio that were previously paid by SendGrid, concurrently with such consummation; provided that solely for purposes of this provision, the term "acquisition proposal" shall have the meaning assigned to such term with respect to SendGrid in "No Solicitation of Alternative Proposals" above, except that the references to "20% or more" shall be deemed to be references to "80% or more".

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available funds, all of Twilio's reasonable and documented out-of-pocket expenses incurred by Twilio or Merger Sub in an amount not to exceed $5 million as promptly as practicable (and, in any event, within two business days following such termination).

        If the merger agreement is terminated (i) by SendGrid following a Twilio triggering event or (ii) by Twilio to enter into a superior proposal, then Twilio shall, within two business days after such termination in the case of clause (i) or concurrently with such termination in the case of clause (ii), pay SendGrid a fee equal to $120 million. Additionally, 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 certain proxies fail to be voted in favor of the issuance of the Twilio Class A common stock in the merger, Twilio will be required to pay SendGrid a fee equal to $120 million as promptly as practicable, and in any event within two business days following such termination.

        Further, if (i) the merger agreement is terminated by Twilio or SendGrid due to a failure to close the merger by the termination date or failure to obtain the Twilio stockholder approval, (ii) prior to such termination referred to in clause (i) of this sentence, but after the date of the merger agreement, a bona fide acquisition proposal with respect to Twilio shall have been publicly made to Twilio or its stockholders and not publicly withdrawn, and (iii) within nine months after the date of a termination in either of the cases referred to in clause (i) of this sentence, Twilio consummates an acquisition proposal with respect to Twilio or enters into an agreement contemplating an acquisition proposal with respect to Twilio that is subsequently consummated, then Twilio shall pay SendGrid a fee equal to $120 million, less any amount of expenses of SendGrid that were previously paid by Twilio, concurrently with such consummation; provided that solely for purposes of this provision, the term "acquisition proposal" shall have the meaning assigned to such term with respect to Twilio in "No Solicitation of Alternative Proposals" above, except that the references to "twenty (20%) or more" shall be deemed to be references to "80% or more". In no event shall SendGrid be required to pay a termination fee or Twilio's expenses on more than one occasion. In no event shall Twilio be required to pay a termination fee or SendGrid's expenses on more than one occasion. Except as discussed above, each party shall pay all fees and expenses incurred by it in connection with the merger and the other transactions contemplated by the merger agreement. Following termination, in addition to any termination fee or expense reimbursement, each party will have the right to pursue damages and other relief for the other party's fraud or intentional and willful breach of any covenant or agreement in the merger agreement.

Amendments and Waivers

        The merger agreement may be amended, modified or supplemented by the parties at any time prior to the effective time of the merger. At any time prior to the effective time of the merger, any party may waive any provision of the merger agreement if, and only if, such waiver is in writing and signed by the party against whom the waiver is to be effective.

Specific Performance

        The parties agreed in the merger agreement that irreparable damage would occur in the event that any of the provisions of the merger agreement were not performed in accordance with their specific terms or were otherwise breached, and that monetary damages would not be an adequate remedy for such occurrence. The parties agreed that they shall be entitled to an injunction or injunctions to prevent breaches of the merger agreement and to enforce specifically the performance of terms and provisions of the merger agreement in addition to any other remedy to which they are entitled at law or in equity.

Merger Agreement Amendment

        On December 13, 2018, the parties amended the merger agreement to change the treatment of the SendGrid UK Options to be as described above in "The Merger Agreement—Treatment of SendGrid Equity Awards" due to a tax ruling that precluded a favorable rollover of the options.

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THE VOTING AGREEMENTS

        The following section summarizes the material provisions of the voting agreements, which are included in this joint proxy statement/prospectus as Annexes D, E, F and G and are incorporated herein by reference in their entirety. The rights and obligations of Twilio and SendGrid are governed by the express terms and conditions of the voting agreements and not by this summary or any other information contained in this joint proxy statement/prospectus. Twilio and SendGrid stockholders are urged to read the voting agreements carefully and in their entirety as well as this joint proxy statement/prospectus before making any decisions regarding the merger, including the approval and adoption of the merger agreement and approval of the Twilio stock issuance. This summary is qualified in its entirety by reference to the voting agreements. The representations, warranties and covenants contained in the voting agreements were made only for purposes of that agreement and as of specific dates, were solely for the benefit of the parties to the voting agreements, may be subject to limitations agreed upon by the parties and may be subject to standards of materiality applicable to the contracting parties that differ from those applicable to investors.

Twilio Voting Agreements

        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 addition, certain persons, including such directors and officers, who hold Twilio Class B common stock irrevocably (to the fullest extent permitted by law) appointed Richard Dalzell, an independent director of Twilio, and Lee Kirkpatrick, in the event Richard Dalzell is no longer a director of Twilio, as the exclusive attorney and proxy of such stockholder. Pursuant to the irrevocable proxies, 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.

        Subject to the terms and conditions set forth in the Twilio voting agreements and the irrevocable proxy, the subject stockholder, directors and executive officers of Twilio agreed, among other things to the fullest extent permitted to do so:

    To appear in person or by proxy at any Twilio stockholders meeting at which a vote with respect to the issuance of shares of Twilio Class A common stock pursuant to the merger agreement is sought, including any adjournment, recess or postponement thereof, or otherwise cause all covered shares to be counted as present at such meetings for purposes of calculating a quorum;

    To vote (or cause to be voted), in person or by proxy, or deliver (or cause to be delivered) a written consent covering, all the covered shares:

    in favor of the approval of the issuance of shares of Twilio Class A common stock pursuant to the merger agreement;

    against any action or agreement that would reasonably be expected to result in a breach in any material respect of any covenant, representation or warranty or any other obligation or agreement of Twilio under the merger agreement; and

    against any Twilio acquisition proposal; and

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    Under the voting agreements (but not the irrevocable proxy) to grant SendGrid an irrevocable proxy to vote all the covered shares which the subject stockholder is permitted to vote.

        The Twilio voting agreements and the irrevocable proxy restrict the subject stockholder, directors and executive officers, among other things, from:

    transferring (or causing or permitting the transfer of) any of the covered shares, or entering into any agreement relating thereto, except:

    by using already-owned covered shares (or effecting a "net exercise" of a Twilio stock option or a "net settlement" of a Twilio RSU) either to pay the exercise price upon the exercise of a Twilio stock option or to satisfy the tax withholding obligation upon the exercise of a Twilio stock option or settlement of a Twilio RSU;

    transferring covered shares to affiliates, immediate family members, a trust established of the benefit of the subject stockholder and/or for the benefit of one or more members of the stockholder's immediate family or charitable organizations;

    transferring covered shares in accordance with the terms of a trading plan established by the subject stockholder pursuant to Rule 10b5-1 under the Exchange Act prior to the date of the voting agreement; or

    with SendGrid's prior written consent and in SendGrid's sole discretion.

        In addition, the stockholder, directors and executive officers subject to the Twilio voting agreements and the irrevocable proxy each agree that they will not, and will not permit their respective representatives to, directly or indirectly:

    solicit, initiate or knowingly induce, knowingly encourage or knowingly facilitate (including by way of furnishing information) any inquiries or the making of any proposal that constitutes, or would reasonably be expected to lead to a Twilio acquisition proposal;

    participate in any discussions or negotiations with any person regarding any proposal the consummation of which would constitute a Twilio acquisition proposal;

    provide any information or data concerning Twilio to any person in connection with any proposal the consummation of which would constitute a Twilio acquisition proposal; or

    approve or recommend, make any public statement approving or recommending, or enter into any agreement related to, any inquiry, proposal or offer that constitutes, or would reasonably be expected to lead to a Twilio acquisition proposal.

        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 in accordance with the terms of such proxies, Twilio will be required to pay a termination fee of $120 million to SendGrid, as more fully described in "The Merger Agreement—Termination Fees and Expenses; Liability for Breach."

SendGrid Voting Agreements

        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 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

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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.

        Subject to the terms and conditions set forth in the SendGrid voting agreements, the subject stockholders, directors and executive officers of SendGrid agreed, among other things to the fullest extent permitted to do so:

    To appear in person or by proxy at any SendGrid stockholders meeting at which a vote with respect to the approval or adoption of the merger agreement and the transactions contemplated thereby is sought, including any adjournment, recess or postponement thereof, or otherwise cause all covered shares to be counted as present at such meetings for purposes of calculating a quorum;

    To vote (or cause to be voted), in person or by proxy, or deliver (or cause to be delivered) a written consent covering, all the covered shares:

    in favor of the merger and the approval and adoption of the merger agreement and the transactions contemplated thereby, including any amendment and restatement of the merger agreement or amendment to the merger agreement, in each case, to the extent such amendment and restatement or amendment increases the merger consideration;

    against any action or agreement that would reasonably be expected to result in a breach in any material respect of any covenant, representation or warranty or any other obligation or agreement of SendGrid under the merger agreement; and

    against any SendGrid acquisition proposal; and

    To grant Twilio an irrevocable proxy to vote all the covered shares which the respective stockholder is permitted to vote.

        The SendGrid voting agreements restrict the subject stockholders, directors and executive officers, among other things, from:

    transferring (or causing or permitting the transfer of) any of the covered shares, or entering into any agreement relating thereto, except:

    by using already-owned covered shares (or effecting a "net exercise" of a SendGrid stock option or a "net settlement" of a SendGrid RSU) either to pay the exercise price upon the exercise of a SendGrid stock option or to satisfy the tax withholding obligation upon the exercise of a SendGrid stock option or settlement of a SendGrid RSU;

    transferring covered shares to affiliates, immediate family members, a trust established of the benefit of the subject stockholder and/or for the benefit of one or more members of the stockholder's immediate family or charitable organizations;

    transferring covered shares in accordance with the terms of a trading plan established by the subject stockholder pursuant to Rule 10b5-1 under the Exchange Act prior to the date of the voting agreement; or

    with Twilio's prior written consent and in Twilio's sole discretion.

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        In addition, the stockholders, directors and executive officers subject to the SendGrid voting agreements each agree that they will not, and will not permit their respective representatives to, directly or indirectly:

    solicit, initiate or knowingly induce, knowingly encourage or knowingly facilitate (including by way of furnishing information) any inquiries or the making of any proposal that constitutes, or would reasonably be expected to lead to a SendGrid acquisition proposal;

    participate in any discussions or negotiations with any person regarding any proposal the consummation of which would constitute a SendGrid acquisition proposal;

    provide any information or data concerning SendGrid to any person in connection with any proposal the consummation of which would constitute a SendGrid acquisition proposal; or

    approve or recommend, make any public statement approving or recommending, or enter into any agreement related to, any inquiry, proposal or offer that constitutes, or would reasonably be expected to lead to a SendGrid acquisition proposal.

        Funds affiliated with Bessemer Venture Partners have advised SendGrid and Twilio, respectively, that they intend to vote or cause to be voted (1) all shares of SendGrid common stock held of record or beneficially owned by them, in favor of the adoption of the merger agreement, the approval of the merger and the other transactions contemplated by the merger agreement, at the SendGrid special meeting or at any adjournment or postponement thereof and (2) all shares of Twilio Class B common stock held of record or beneficially owned by them in favor of the approval of the issuance of shares of Twilio Class A common stock pursuant to the merger agreement, at the Twilio special meeting or at any adjournment or postponement thereof.

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THE MERGER

        This section and the section entitled "The Merger Agreement" describe the material aspects of the merger, including the merger agreement. While Twilio and SendGrid believe that the following description covers the material terms of the merger, the description may not contain all of the information that is important to you. Twilio and SendGrid encourage you to read carefully this entire joint proxy statement/prospectus, including the merger agreement attached to this joint proxy statement/prospectus as Annex A, for a more complete understanding of the merger.

Background of the Merger

        Over the years, in the ordinary course from time to time, the boards of directors and management teams of SendGrid and Twilio have each separately evaluated and considered a variety of financial and strategic opportunities for their respective companies as part of their respective long-term strategies to enhance value for their stockholders, including potential acquisitions, divestitures, business combinations and other transactions.

        On August 21, 2017, SendGrid filed with the Securities and Exchange Commission a confidential, draft registration statement for its proposed initial public offering or IPO.

        On September 1, 2017, during a meeting, Jeffrey Lawson, the Chief Executive Officer of Twilio, indicated to Sameer Dholakia, the Chief Executive Officer of SendGrid, that Twilio was interested in exploring a potential strategic transaction with SendGrid without proposing any detailed terms, including any price or form of consideration. Mr. Dholakia indicated that he would share this interest with the SendGrid Board.

        On September 4, 2017, the SendGrid Board met, with SendGrid senior management attending, and discussed the fact that SendGrid had received in-bound interest from Twilio exploring a potential strategic transaction, and from a private equity sponsor expressing an interest in acquiring SendGrid for cash. Prior to the discussion, the SendGrid Board noted that Bryon Deeter, one of the members of the SendGrid Board and a partner of Bessemer Venture Partners ("Bessemer") is also a member of the Twilio Board. The SendGrid Board determined that Mr. Deeter would be recused from the portion of any future meetings during which a possible transaction with Twilio would be discussed. The SendGrid Board also discussed whether other potential conflicts might exist and did not identify other conflicts. Mr. Deeter then joined the meeting and the SendGrid Board discussed whether SendGrid should explore a sale of the company as an alternative to an IPO, without discussing the merits of pursuing a transaction with any particular counterparty, including Twilio. The SendGrid Board was supportive of exploring a potential sale while continuing in parallel to pursue the IPO.

        On September 6, 2017, at a regularly scheduled meeting of the Twilio Board, Mr. Lawson reported on the discussions with SendGrid, and representatives of Twilio management addressed the potential benefits of a transaction with SendGrid. The Twilio Board supported further exploration of the merits of such transaction, including the exchange of confidential information.

        On September 22, 2017, the SendGrid Board met, with SendGrid senior management attending, and discussed the pending IPO and the inbound expressions of interest from each of Twilio and the private equity sponsor. Mr. Deeter recused himself from the portion of the meeting where the potential sale alternative, including the benefits and associated risks of such alternative, was discussed. The SendGrid Board authorized SendGrid senior management to engage in discussions with Twilio and the private equity sponsor and also authorized an outreach to other potential strategic parties to determine if they had any interest in acquiring SendGrid before SendGrid completed its pending IPO.

        Consistent with the SendGrid Board's direction, after the September 22, 2017 SendGrid Board meeting, SendGrid senior management and representatives of Morgan Stanley, who was serving as the lead underwriter for SendGrid's proposed IPO, contacted four other strategic parties to determine

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interest in discussing an acquisition of SendGrid. Only one of the four parties who were contacted agreed to hold an initial meeting with SendGrid. Ultimately, none of them expressed an interest in pursuing a potential acquisition of SendGrid.

        On September 27, 2017, Mr. Dholakia and Yancey Spruill, the Chief Financial Officer of SendGrid, met with representatives of Twilio senior management and the parties exchanged nonpublic financial information under a mutual confidentiality agreement, previously entered into on September 8, 2017, which did not contain any standstill obligation.

        In early October 2017, Mr. Lawson made a verbal proposal to Mr. Dholakia to acquire SendGrid for $650 million without specifying the form of consideration to be paid (the "2017 Twilio Initial Proposal"). Mr. Dholakia promptly conveyed the 2017 Twilio Initial Proposal to the SendGrid Board other than Mr. Deeter.

        On October 13, 2017, the SendGrid Board met, with SendGrid senior management and representatives of each of Morgan Stanley, as its lead underwriter, and Cooley LLP, SendGrid's outside legal counsel, attending. Mr. Dholakia provided an update on the business and financial results of SendGrid and the status of the pending IPO and the SendGrid Board discussed the range of likely valuations of SendGrid in the IPO. The SendGrid Board then approved matters relating to the IPO. Mr. Deeter then recused himself and the SendGrid Board next discussed the merits of the 2017 Twilio Initial Proposal as an alternative to the IPO. After discussion, the SendGrid Board determined that the 2017 Twilio Initial Proposal was inadequate and that SendGrid should continue to pursue completion of the IPO. Mr. Dholakia promptly communicated the SendGrid Board's rejection to Mr. Lawson.

        On October 25, 2017, Mr. Spruill and Laurence Trifon, Vice President of Corporate Development of SendGrid, had a call with representatives of Twilio senior management, including Mr. Lawson and Lee Kirkpatrick, Chief Financial Officer of Twilio, to discuss certain financial and business aspects of SendGrid and Twilio.

        On October 26, 2017, during a regularly scheduled SendGrid Board meeting, with SendGrid senior management attending, Mr. Lawson called Mr. Dholakia to increase the offer price to $750 million without specifying the form of consideration to be paid (the "2017 Twilio Second Proposal"). Mr. Deeter recused himself during the discussion of the 2017 Twilio Second Proposal. The SendGrid Board discussed the merits of 2017 Twilio Second Proposal. Mr. Dholakia also informed the SendGrid Board that the private equity sponsor had verbally conveyed a potential range of values for a cash acquisition, subject to confirmation following due diligence. Mr. Dholakia noted that the potential range of values was below likely values in the IPO and that he had informed the sponsor that the range was not compelling. Following discussions, the SendGrid Board determined that the 2017 Twilio Second Proposal still did not provide adequate value for SendGrid and its stockholders compared to the IPO alternative. Mr. Dholakia conveyed to Mr. Lawson the SendGrid Board's rejection of the 2017 Twilio Second Proposal.

        On October 27, 2017, following a series of discussions between Messrs. Dholakia and Lawson, Mr. Lawson made a proposal to Mr. Dholakia that Twilio would acquire SendGrid for $900 million without specifying the form of consideration to be paid (the "2017 Twilio Third Proposal").

        On October 28, 2017, the SendGrid Board met, with SendGrid senior management attending, to discuss the 2017 Twilio Third Proposal and the IPO. Mr. Deeter recused himself during the discussion of the 2017 Twilio Third Proposal. The SendGrid Board determined that the 2017 Twilio Third Proposal did not provide adequate value for SendGrid and its stockholders in comparison to the potential stockholder value to be achieved by executing the standalone plan, including completing the pending IPO. The SendGrid Board authorized SendGrid management to proceed with causing the registration statement for the IPO to be filed publicly and completing the IPO. The SendGrid Board further authorized SendGrid senior management to engage in discussions with Twilio regarding

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potential commercial partnering arrangements. Following the meeting, Mr. Dholakia conveyed to Mr. Lawson the SendGrid Board's rejection of the 2017 Twilio Third Proposal.

        On November 14, 2017, SendGrid priced its IPO at $16.00 per share of SendGrid common stock, which represented an implied equity value of SendGrid of approximately $864 million. On November 15, 2017, the first day when the SendGrid common stock was traded on the NYSE, the closing price per share of the SendGrid common stock was $18.00, which represented an implied equity value of SendGrid of approximately $972 million.

        Following the IPO, Mr. Lawson and Mr. Dholakia continued to maintain contact from time to time concerning general business developments impacting the industry and potential commercial partnering arrangement opportunities between SendGrid and Twilio.

        On May 22, 2018, Messrs. Dholakia and Lawson met at a media dinner hosted for senior executives by Bessemer and, after the media dinner, they discussed the possibility of resuming discussions regarding a possible acquisition of SendGrid by Twilio. No representatives of Bessemer participated in such discussions. Mr. Dholakia indicated to Mr. Lawson that the SendGrid Board would be open to a discussion because the combination of Twilio and SendGrid makes strategic sense, but whether the SendGrid Board would ultimately support an acquisition would depend on price and other terms offered by Twilio.

        On June 4, 2018, Mr. Lawson called Mr. Dholakia indicating an interest in Twilio acquiring SendGrid and that he would direct the Twilio management team to conduct an analysis on certain aspects of a potential acquisition of and would confirm in early July 2018 Twilio's interest, if any, in pursuing a potential acquisition of SendGrid.

        On July 12, 2018, Mr. Lawson reached out to Mr. Dholakia to confirm Twilio's interest in pursuing a potential acquisition of SendGrid. Following discussions, Messrs. Dholakia and Lawson agreed to continue more detailed discussions and due diligence under a mutual confidentiality agreement, and agreed to schedule an in-person meeting for the members of the management team of each party later in July 2018.

        On July 16, 2018, Twilio sent SendGrid a proposed mutual confidentiality agreement to govern potential discussions regarding a strategic transaction between the parties. The parties executed the confidentiality agreement on July 18, 2018, which included a 12-month standstill provision for the benefit of SendGrid that would permit Twilio to make a confidential proposal to SendGrid or the SendGrid Board if SendGrid entered into a definitive agreement with a third party for a change of control transaction. This confidentiality agreement superseded the September 2017 confidentiality agreement between SendGrid and Twilio.