As filed with the Securities and Exchange Commission on August 2, 2021

Registration No. 333-            

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-3

REGISTRATION STATEMENT

Under

The Securities Act of 1933

Twilio Inc.

(Exact name of Registrant as specified in its charter)

101 Spear Street, First Floor

San Francisco, California 94105

Tel: (415) 390-2337

(Address, including zip code, and telephone number, including area code, of Registrant’s principal executive offices)

Jeffrey Lawson

Chief Executive Officer

101 Spear Street, First Floor

San Francisco, California 94105

(415) 390-2337

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Approximate date of commencement of proposed sale to the public: From time to time after the effective date of this Registration Statement.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box:  ☐

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, as amended, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box:  ☒

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

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

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box.  ☒

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box.  ☐

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

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

CALCULATION OF REGISTRATION FEE

PROSPECTUS

Class A Common Stock

This prospectus relates to the proposed resale from time to time of up to 1,175,923 shares of our Class A common stock, par value $0.001 per share, by the selling stockholders named herein. The selling stockholders (which term as used herein, includes their respective transferees, pledgees, distributees, donees, and successors) acquired these shares from us pursuant to an Agreement and Plan of Reorganization, dated May 16, 2021, by and among us, Zeus Merger Sub I, Inc., Zeus Merger Sub II, LLC, Zipwhip, Inc. (“Zipwhip”), and Fortis Advisors LLC, as the Stockholder Representative.

The selling stockholders may offer and sell or otherwise dispose of the shares of Class A common stock described in this prospectus from time to time through public or private transactions at prevailing market prices, at prices related to prevailing market prices, or at privately negotiated prices. The selling stockholders will bear all underwriting fees, commissions, and discounts, if any, attributable to the sales of shares and any transfer taxes. We will bear all other costs, expenses, and fees in connection with the registration of the shares. See “Plan of Distribution” for more information about how the selling stockholders may sell or dispose of their shares of Class A common stock.

We will not receive any proceeds from the sale of the shares by the selling stockholders.

Our Class A common stock is listed on the New York Stock Exchange under the trading symbol “TWLO.” On July 30, 2021, the last reported sale price of our Class A common stock was $373.59 per share.

Investing in our Class A common stock involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “Risk Factors” on page 4 of this prospectus, as well as under similar headings in the other documents that are incorporated by reference into this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is August 2, 2021.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS

This prospectus is part of an automatic registration statement on Form S-3 that we filed with the Securities and Exchange Commission (“SEC”), using a “shelf” registration process as a “well-known seasoned issuer” as defined in Rule 405 under the Securities Act of 1933, as amended (the “Securities Act”). You should rely only on the information contained, or incorporated by reference, in this prospectus and any accompanying prospectus supplement, and any free writing prospectus we authorize for use in connection with the applicable offering. We have not authorized anyone to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. You should assume that the information in this prospectus, any accompanying prospectus supplement, the documents incorporated by reference herein or therein, and any free writing prospectus we have authorized for use in connection with the applicable offering is accurate or complete only as of their respective dates, regardless of the time of delivery of this prospectus, the accompanying prospectus supplement, and any authorized free writing prospectus. Our business, financial condition, results of operations, and prospects may have changed since those dates.

In this prospectus, as permitted by law, we “incorporate by reference” information from other documents that we file with the SEC. This means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be a part of this prospectus and any accompanying prospectus and should be read with the same care. When we update the information contained in documents that have been incorporated by reference by making future filings with the SEC, the information included or incorporated by reference in this prospectus is considered to be automatically updated and superseded. In other words, in case of a conflict or inconsistency between information contained in this prospectus and information in any accompanying prospectus supplement or incorporated by reference into this prospectus, you should rely on the information contained in the document that was filed later. See “Incorporation of Certain Information by Reference” in this prospectus.

This prospectus and the accompanying prospectus supplement do not constitute an offer to sell or the solicitation of an offer to buy any securities other than the securities described in the accompanying prospectus supplement or an offer to sell or the solicitation of an offer to buy such securities in any circumstances in which such offer or solicitation is unlawful.

Unless the context otherwise requires, the terms “Twilio,” “the Company,” “we,” “us,” and “our” in this prospectus refer to Twilio Inc. and its consolidated subsidiaries.

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RISK FACTORS

Investing in our Class A common stock involves a high degree of risk. Before deciding whether to purchase our Class A common stock, you should consider carefully the risks and uncertainties discussed under the section titled “Risk Factors” contained in our most recent Annual Report on Form 10-K, as updated by our subsequent Quarterly Reports on Form 10-Q and other filings we make with the SEC, which are incorporated by reference into this prospectus in their entirety, together with other information in this prospectus and the documents incorporated by reference. The risks described in these documents are not the only ones we face, but those that we consider to be material. There may be other unknown or unpredictable economic, business, competitive, regulatory, or other factors that could have material adverse effects on our future results. Past financial performance may not be a reliable indicator of future performance, and historical trends should not be used to anticipate results or trends in future periods. If any of these risks actually occurs, our business, financial condition, results of operations, or cash flow could be seriously harmed. This could cause the trading price of our securities to decline, resulting in a loss of all or part of your investment. Please also read carefully the section below titled “Special Note Regarding Forward-Looking Statements.”

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, as well as the documents we have filed with the SEC that are incorporated by reference in this prospectus, contain “forward-looking statements” within the meaning of Section 27A of the Securities Act, and Section 21E of the Exchange Act. These statements relate to future events or to our future operating or financial performance and involve known and unknown risks, uncertainties, and other factors that may cause our actual results, performance, or achievements to be materially different from any future results, performances, or achievements expressed or implied by the forward-looking statements. All statements other than statements of historical facts contained in this prospectus, including statements regarding our future results of operations and financial condition, business strategy, and plans and objectives of management for future operations, are forward-looking statements. In some cases, forward-looking statements may be identified by words such as “anticipate,” “believe,” “continue,” “could,” “design,” “estimate,” “expect,” “intend,” “may,” “plan,” “potentially,” “predict,” “project,” “should,” “will,” or the negative of these terms or other similar expressions.

We have based these forward-looking statements largely on our current expectations and projections about future events and financial trends that we believe may affect our financial condition, results of operations, business strategy, and financial needs. These forward-looking statements are subject to a number of known and unknown risks, uncertainties, and assumptions, including risks described in the section titled “Risk Factors” and elsewhere in this prospectus and in our most recent Annual Report on Form 10-K, as updated by our subsequent Quarterly Reports on Form 10-Q and other filings we make with the SEC, which are incorporated by reference into this prospectus in their entirety, together with other information in this prospectus and the documents incorporated by reference. These factors include, among other things:

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These risks are not exhaustive. Other sections of this prospectus may include additional factors that could harm our business and financial performance. Moreover, we operate in a very competitive and rapidly changing environment. New risk factors emerge from time to time, and it is not possible for management to predict all risk factors nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ from those contained in, or implied by, any forward-looking statements.

We intend to continue to evaluate and consider potential strategic transactions, including acquisitions of companies of similar or larger size than Zipwhip, and such acquisitions may include the issuance of our Class A common stock as consideration, resulting in dilution to existing stockholders. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, joint ventures or investments we may make.

You should not rely upon forward-looking statements as predictions of future events. We cannot assure you that the events and circumstances reflected in the forward-looking statements will be achieved or occur.

Although we believe that the expectations reflected in the forward-looking statements are reasonable, we cannot guarantee future results, levels of activity, performance, or achievements. Except as required by law, we undertake no obligation to update publicly any forward-looking statements for any reason after the date of this prospectus or to conform these statements to actual results or to changes in our expectations.

In addition, statements that “we believe” and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this prospectus, and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all relevant information. These statements are inherently uncertain and investors are cautioned not to unduly rely upon these statements.

You should read this prospectus and the documents that we reference in this prospectus and have filed as exhibits to the registration statement of which this prospectus is a part with the understanding that our actual future results, levels of activity, performance, and achievements may be different from what we expect. We qualify all of our forward-looking statements by these cautionary statements.

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USE OF PROCEEDS

All of the shares of Class A common stock being offered hereby are being sold by the selling stockholders identified in this prospectus. We will not receive any proceeds from the sale of the Class A common stock by the selling stockholders. We will be responsible for the out-of-pocket costs, expenses and fees incurred in connection with the registration of the shares to be sold by the selling stockholders, including registration, listing fees, printers and accounting fees, and fees and disbursements of counsel (collectively, the “Registration Expenses”). Other than Registration Expenses, the selling stockholders will be responsible for underwriting discounts, commissions, placement agent fees, or other similar expenses payable with respect to sales of shares.

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DESCRIPTION OF CAPITAL STOCK

General

As of the date of this prospectus, our authorized capital stock consists of shares, all with a par value of $0.001 per share, of which:

A description of the material terms and provisions of our amended and restated certificate of incorporation and second amended and restated bylaws affecting the rights of holders of our capital stock is set forth below. The description is intended as a summary, and is qualified in its entirety by reference to our amended and restated certificate of incorporation and our second amended and restated bylaws which are incorporated by reference into the registration statement of which this prospectus is a part.

Class A and Class B Common Stock

Except with respect to voting, conversion, and transfer rights as described below and as otherwise expressly provided in our amended and restated certificate of incorporation or required by applicable law, shares of Class A common stock and Class B common stock have the same rights and privileges and rank equally, share ratably, and are identical in all respects as to all matters.

Dividend Rights

Subject to preferences that may apply to any shares of preferred stock outstanding at the time, the holders of Class A and Class B common stock are entitled to receive dividends out of funds legally available if the board of directors, in its discretion, determines to issue dividends and then only at the times and in the amounts that the board of directors may determine.

Voting Rights

Holders of our Class A common stock are entitled to one vote for each share of Class A common stock held on all matters submitted to a vote of stockholders and holders of our Class B common stock are entitled to 10 votes for each share of Class B common stock held on all matters submitted to a vote of stockholders. Holders of shares of our Class A common stock and Class B common stock vote together as a single class on all matters (including the election of directors) submitted to a vote of stockholders, unless otherwise required by law. We have not provided for cumulative voting for the election of directors in our amended and restated certificate of incorporation. Our amended and restated certificate of incorporation and second amended and restated bylaws provide for a classified board of directors consisting of three classes of approximately equal size, each serving staggered three-year terms.

No Preemptive or Similar Rights

Our Class A and Class B common stock are not entitled to preemptive rights, and are not subject to conversion, redemption or sinking fund provisions, except for the conversion provisions with respect to the Class B common stock described below.

Liquidation Rights

If we become subject to a liquidation, dissolution or winding-up, the assets legally available for distribution to our stockholders would be distributable ratably among the holders of our Class A and Class B common stock and any participating preferred stock outstanding at that time, subject to prior satisfaction of all outstanding debt and

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liabilities and the preferential rights of and the payment of liquidation preferences, if any, on any outstanding shares of preferred stock.

Fully Paid and Non-Assessable

All of the outstanding shares of our common stock are fully paid and non-assessable.

Subdivisions and Combinations

If we subdivide or combine in any manner outstanding shares of Class A common stock or Class B common stock, then the outstanding shares of all common stock will be subdivided or combined in the same proportion and manner.

Conversion

Each outstanding share of Class B common stock is convertible at any time at the option of the holder into one share of Class A common stock. In addition, each share of Class B common stock will convert automatically into one share of Class A common stock upon any transfer, whether or not for value, except for certain permitted transfers described in our amended and restated certificate of incorporation, including transfers to family members, trusts solely for the benefit of the stockholder or their family members, and partnerships, corporations, and other entities exclusively owned by the stockholder or their family members. Once converted or transferred and converted into Class A common stock, the Class B common stock will not be reissued.

All the outstanding shares of Class A and Class B common stock will convert automatically into shares of a single class of common stock on the earlier of June 28, 2023 or the date the holders of two-thirds of our Class B common stock elect to convert the Class B common stock to Class A common stock. Following such conversion, each share of common stock will have one vote per share and the rights of the holders of all outstanding common stock will be identical. Once converted into a single class of common stock, the Class A and Class B common stock may not be reissued.

Preferred Stock

The board of directors is authorized, subject to limitations prescribed by Delaware law, to issue preferred stock in one or more series, to establish from time to time the number of shares to be included in each series and to fix the designation, powers, preferences and rights of the shares of each series and any of its qualifications, limitations or restrictions, in each case without further vote or action by our stockholders. The board of directors can also increase or decrease the number of shares of any series of preferred stock, but not below the number of shares of that series then outstanding, without any further vote or action by our stockholders. The board of directors may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of our Class A or Class B common stock. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions and other corporate purposes, could, among other things, have the effect of delaying, deferring or preventing a change in control of Twilio and might adversely affect the market price of Class A common stock and the voting and other rights of the holders of our Class A and Class B common stock. We have no current plan to issue any shares of preferred stock.

Anti-Takeover Provisions

Anti-Takeover Statute

We are governed by the provisions of Section 203 of the Delaware General Corporations Law (“DGCL”), which generally prohibits a publicly held Delaware corporation from engaging in any business combination with any interested stockholder for a period of three years after the date that such stockholder became an interested stockholder, with the following exceptions:

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In general, Section 203 defines a “business combination” to include the following:

In general, Section 203 defines an “interested stockholder” as an entity or person who, together with the person’s affiliates and associates, beneficially owns, or within three years prior to the time of determination of interested stockholder status did own, 15% or more of the outstanding voting stock of the corporation.

Amended and Restated Certificate of Incorporation and Second Amended and Restated Bylaws

Our amended and restated certificate of incorporation and second amended and restated bylaws include a number of provisions that could deter hostile takeovers or delay or prevent changes in control of the Company, as well as changes in the board of directors or management team, including the following:

Board of Directors Vacancies. Our amended and restated certificate of incorporation and second amended and restated bylaws authorize only the board of directors to fill vacant directorships, including newly created seats. In

addition, the number of directors constituting the board of directors is permitted to be set only by a resolution adopted by a majority vote of the entire board of directors. These provisions prevent a stockholder from increasing the size of the board of directors and then gaining control of the board of directors by filling the resulting vacancies with its own nominees. This makes it more difficult to change the composition of the board of directors and will promote continuity of management.

Dual Class Common Stock. As described above in “—Class A and Class B Common Stock—Voting Rights,” our amended and restated certificate of incorporation provides for a dual class common stock structure pursuant to which holders of our Class B common stock have the ability to control the outcome of matters requiring stockholder approval, even if they own significantly less than a majority of the shares of the outstanding Class A and Class B common stock, including the election of directors and significant corporate transactions, such as a merger or other sale of the Company or its assets. Current investors, executives and employees have the ability to exercise significant influence over those matters.

Classified Board. Our amended and restated certificate of incorporation and second amended and restated bylaws provide that the board of directors be classified into three classes of directors, each of which hold office for a

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three-year term. In addition, directors may only be removed from the board of directors for cause. The existence of a classified board could delay a potential acquiror from obtaining majority control of the board of directors, and the prospect of that delay might deter a potential acquiror.

Stockholder Action; Special Meeting of Stockholders. Our amended and restated certificate of incorporation provides that our stockholders may not take action by written consent, but may only take action at annual or special meetings of stockholders. As a result, a holder controlling a majority of our capital stock would not be able to amend our second amended and restated bylaws or remove directors without holding a meeting of stockholders called in accordance with our second amended and restated bylaws. Our second amended and restated bylaws further provide that special meetings of stockholders may be called only by a majority of the board of directors, the chairman of the board of directors, our Chief Executive Officer or our President, thus prohibiting a stockholder from calling a special meeting. These provisions might delay the ability of our stockholders to force consideration of a proposal or for stockholders controlling a majority of our capital stock to take any action, including the removal of directors.

Advance Notice Requirements for Stockholder Proposals and Director Nominations. Our second amended and restated bylaws provide advance notice procedures for stockholders seeking to bring business before our annual meeting of stockholders or to nominate candidates for election as directors at our annual meeting of stockholders. Our second amended and restated bylaws also specify certain requirements regarding the form and content of a stockholder’s notice. These provisions might preclude our stockholders from bringing matters before our annual meeting of stockholders or from making nominations for directors at our annual meeting of stockholders if the proper procedures are not followed. These provisions may also discourage or deter a potential acquiror from conducting a solicitation of proxies to elect the acquiror’s own slate of directors or otherwise attempting to obtain control of Twilio.

No Cumulative Voting. The DGCL provides that stockholders are not entitled to cumulate votes in the election of directors unless a corporation’s certificate of incorporation provides otherwise. Our amended and restated certificate of incorporation does not provide for cumulative voting.

Directors Removed Only for Cause. Our amended and restated certificate of incorporation provides that stockholders may remove directors only for cause.

Amendment of Charter Provisions. Any amendment of the above provisions in our amended and restated certificate of incorporation requires approval by holders of at least two-thirds of the then-outstanding capital stock.

Issuance of Undesignated Preferred Stock. The board of directors has the authority, without further action by our stockholders, to issue up to 100,000,000 shares of undesignated preferred stock with rights and preferences, including voting rights, designated from time to time by the board of directors. The existence of authorized but unissued shares of preferred stock would enable the board of directors to render more difficult or to discourage an attempt to obtain control of Twilio by means of a merger, tender offer, proxy contest or other means.

Choice of Forum. Our second amended and restated bylaws provide that, unless we consent in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware shall be the sole and exclusive forum to bring any state law claims for (i) any derivative action or proceeding brought on our behalf, (ii) any action asserting a claim of, or a claim based on, breach of a fiduciary duty owed by any of our current or former directors, officers, or other employees or stockholders to us or our stockholders, (iii) any action asserting a claim against us or any of our current or former directors, officers, or other employees or stockholders arising pursuant to any provision of the DGCL or our amended and restated certificate of incorporation or second amended and restated bylaws, or (iv) any action asserting a claim against us or any of our current or former directors, officers, or other employees or stockholders governed by the internal affairs doctrine. Unless we consent in writing to the selection of an alternative forum, the United States District Court for the Northern District of California shall be

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the sole and exclusive forum for resolving any complaint asserting a cause of action arising under the Securities Act. Our second amended and restated bylaws also provide that any person or entity purchasing or otherwise acquiring any interest in shares of our capital stock shall be deemed to have notice of and consented to these choice of forum provisions.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A. The transfer agent and registrar’s address is c/o: Shareholder Services, 462 South 4th Street, Suite 1600, Louisville KY 40202.

Listing

Our Class A common stock is listed on the New York Stock Exchange under the symbol “TWLO.”

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SELLING STOCKHOLDERS

We have prepared this prospectus to allow the selling stockholders to offer and sell from time to time up to 1,175,923 shares of our Class A common stock for their own account. We are registering the offer and sale of the shares beneficially owned by the selling stockholders to satisfy certain registration obligations in connection with our acquisition of Zipwhip (the “Merger”). Pursuant to the Agreement and Plan of Reorganization, dated May 16, 2021 (the “Merger Agreement”), we have agreed to keep the registration statement of which this prospectus forms a part effective until the earlier of (i) July 14, 2022, (ii) the date on which all of the shares have been sold pursuant to the registration statement or otherwise, (iii) the date on which all of the shares may be transferred pursuant to Rule 144 under the Securities Act or another similar exemption under the Securities Act without manner of sale or volume restrictions, or (iv) the date on which all of the shares cease to be outstanding.

The following table sets forth (i) the name of each selling stockholder, (ii) the number of shares beneficially owned by each of the respective selling stockholders, including the shares over which the selling stockholder has sole or shared voting power or investment power and also any shares that the selling stockholder has the right to acquire within 60 days of such date through the exercise of any options or other rights, (iii) the number of shares that may be offered under this prospectus, and (iv) the number of shares of our Class A common stock beneficially owned by the selling stockholders assuming all of the shares covered hereby are sold. We do not know how long the selling stockholders will hold the shares before selling them, and we currently have no agreements, arrangements, or understandings with the selling stockholders regarding the sale or other disposition of any shares. Except as disclosed in the footnotes to the table below, to our knowledge, none of the selling stockholders listed in the table below has, or during the three years prior to the date of this prospectus has had, any position, office, or other material relationships with us or any of our affiliates.

The information set forth in the table below is based upon information obtained from the selling stockholders. Beneficial ownership of the selling stockholders is determined in accordance with Rule 13d-3(d) under the Exchange Act. The percentage of shares beneficially owned prior to, and after, the offering is based on 165,715,499 shares of Class A common stock and 10,218,422 shares of Class B common stock outstanding as of June 30, 2021, and excludes the issuance of 1,175,923 shares of Class A common stock upon the closing of the Merger on July 14, 2021.

As used in this prospectus, the term “selling stockholders” includes the selling stockholders listed in the table below and any of their transferees, pledgees, distributees, donees and successors.

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PLAN OF DISTRIBUTION

We are registering the shares of Class A common stock held by the selling stockholders to be sold from time to time after the date of this prospectus. We will not receive any of the proceeds from the sale by the selling stockholders of the shares of Class A common stock.

Each selling stockholder of the Class A common stock and any of its transferees, pledgees, distributees, donees, and successors may, from time to time, sell any or all of their securities covered hereby on the principal trading market for the Class A common stock or any other stock exchange, market, or trading facility on which the Class A common stock is traded or in private transactions. These sales may be at fixed or negotiated prices. A selling stockholder may use any one or more of the following methods when selling securities:

The selling stockholders may elect to make a pro rata in-kind distribution of their shares of Class A common stock to their respective members, partners, or stockholders. To the extent that such members, partners, or stockholders are not affiliates of ours, such members, partners, or stockholders would thereby receive freely tradeable shares of our Class A common stock pursuant to the distribution through a registration statement.

The selling stockholders may also sell the shares of Class A common stock under Rule 144 or any other exemption from registration under the Securities Act, if available, rather than under this prospectus.

The selling stockholders also may transfer the shares of Class A common stock in other circumstances, in which case the transferees or other successors in interest will be the selling beneficial owners for purposes of this prospectus.

Broker-dealers engaged by the selling stockholders may arrange for other brokers-dealers to participate in sales. Broker-dealers may receive commissions or discounts from the selling stockholders (or, if any broker-dealer acts as agent for the purchaser of Class A common stock, from the purchaser) in amounts to be negotiated, but, except as set forth in a supplement to this prospectus, in the case of an agency transaction not in excess of a customary brokerage commission in compliance with Financial Industry Regulatory Authority (“FINRA”) Rule 5110; and in the case of a principal transaction a markup or markdown in compliance with FINRA Rule 2121.

In connection with the sale of the Class A common stock or interests therein, the selling stockholders may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn engage in short sales of the Class A common stock in the course of hedging the positions they assume. The selling stockholders

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may also sell Class A common stock short and deliver these shares to close out their short positions, or loan or pledge the securities to broker-dealers that in turn may sell these shares. The selling stockholders may also enter into option or other transactions with broker-dealers or other financial institutions or create one or more derivative securities which require the delivery to such broker-dealer or other financial institution of securities offered by this prospectus, which securities such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

The selling stockholders and any broker-dealers or agents that are involved in selling the securities may be deemed to be “underwriters” within the meaning of the Securities Act in connection with such sales. In such event, any commissions received by such broker-dealers or agents and any profit on the resale of the shares of Class A common stock purchased by them may be deemed to be underwriting commissions or discounts under the Securities Act. Each selling stockholder has informed us that it does not have any written or oral agreement or understanding, directly or indirectly, with any person to distribute the shares of Class A common stock.

We are required to pay certain fees and expenses incurred by us incident to the registration of the shares of Class A common stock. We have agreed to indemnify the selling stockholders against certain losses, claims, damages, and liabilities, including liabilities under the Securities Act.

The resale securities will be sold only through registered or licensed brokers or dealers if required under applicable state securities laws. In addition, in certain states, the resale securities covered hereby may not be sold unless they have been registered or qualified for sale in the applicable state or an exemption from the registration or qualification requirement is available and is complied with.

Under applicable rules and regulations under the Exchange Act, any person engaged in the distribution of the resale shares of Class A common stock may not simultaneously engage in market making activities with respect to the Class A common stock for the applicable restricted period, as defined in Regulation M, prior to the commencement of the distribution. In addition, the selling stockholders will be subject to applicable provisions of the Exchange Act and the rules and regulations thereunder, including Regulation M, which may limit the timing of purchases and sales of the Class A common stock by the selling stockholders or any other person. We will make copies of this prospectus available to the selling stockholders and have informed them of the need to deliver a copy of this prospectus to each purchaser at or prior to the time of the sale (including by compliance with Rule 172 under the Securities Act).

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LEGAL MATTERS

Fenwick & West LLP, New York, will pass upon the validity of the shares of Class A common stock offered by this prospectus.

EXPERTS

The consolidated financial statements of Twilio Inc. as of December 31, 2020 and 2019, and for each of the years in the three-year period ended December 31, 2020, and management’s assessment of the effectiveness of internal control over financial reporting as of December 31, 2020 have been incorporated by reference herein in reliance on the reports of KPMG LLP, an independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

The audit report on the effectiveness of internal control over financial reporting as of December 31, 2020, contains an explanatory paragraph that states that the Company acquired Segment.io, Inc. (“Segment”) during fiscal 2020, and management excluded from its assessment of the effectiveness of the Company’s internal control over financial reporting as of December 31, 2020, Segment’s internal control over financial reporting associated with $253.6 million, or 3%, of the Company’s total assets and $23.0 million, or 1%, of consolidated revenues included in the consolidated financial statements as of and for the year ended December 31, 2020. KPMG LLP’s audit of internal control over financial reporting of the Company also excluded an evaluation of the internal control over financial reporting of Segment.

KPMG LLP’s report on the Company’s consolidated financial statements refers to the change in method of accounting for leases on the adoption of Financial Accounting Standards Board’s Accounting Standards Codification (ASC) Topic 842, Leases, as of January 1, 2019.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus is part of the registration statement on Form S-3 we filed with the SEC under the Securities Act and does not contain all the information set forth or incorporated by reference in the registration statement. Whenever a reference is made in this prospectus to any of our contracts, agreements, or other documents, the reference may not be complete and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other documents incorporated by reference into this prospectus for a copy of such contract, agreement, or other document. Because we are subject to the information and reporting requirements of the Exchange Act, we file annual, quarterly, and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC’s website at http://www.sec.gov. Our Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K, including any amendments to those reports, and other information that we file with or furnish to the SEC pursuant to Section 13(a) or 15(d) of the Exchange Act can also be accessed free of charge on the Investor Relations section of our website, which is located at www.investors.twilio.com. These filings will be available as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC.

Our website address is www.twilio.com. Information contained on or accessible through our website is not a part of this prospectus and is not incorporated by reference herein, and the inclusion of our website address in this prospectus is an inactive textual reference only.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus. Information in this prospectus supersedes

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information incorporated by reference that we filed with the SEC prior to the date of this prospectus, while information that we file later with the SEC will automatically update and supersede the information in this prospectus. We incorporate by reference into this prospectus and the registration statement of which this prospectus is a part the information or documents listed below that we have filed with the SEC (Commission File No. 001-37806):

We also incorporate by reference any future filings (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items unless such Form 8-K expressly provides to the contrary) made with the SEC pursuant to Sections 13(a), 13(c), 14, or 15(d) of the Exchange Act that are filed after the date of the initial registration statement and prior to the effectiveness of the registration statement or that are filed after the effective date of the registration statement of which this prospectus is a part and prior to the termination of the offering of securities offered pursuant to this prospectus. Any information in such future filings updates and supplements the information provided in this prospectus. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later filed document modify or replace such earlier statements.

You can request a copy of these filings, at no cost, by writing or telephoning us at the following address or telephone number:

Twilio Inc.

Attn: General Counsel

101 Spear Street, First Floor

San Francisco, CA 94105

(415) 390-2337

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PART II

INFORMATION NOT REQUIRED IN THE PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution

The following table sets forth an estimate of the fees and expenses, other than the underwriting discounts and commissions, payable by us in connection with the issuance and distribution of the securities being registered. All the amounts shown are estimates, except for the SEC registration fee.

Item 15. Indemnification of Directors and Officers

Section 145 of the DGCL authorizes a court to award, or a corporation’s board of directors to grant, indemnity to directors and officers in terms sufficiently broad to permit such indemnification under certain circumstances for liabilities, including reimbursement for expenses incurred, arising under the Securities Act. Our amended and restated certificate of incorporation provides for indemnification of our directors, officers, employees, and other agents to the maximum extent permitted by the DGCL, and our second amended and restated bylaws provide for indemnification of our directors, officers, employees, and other agents to the maximum extent permitted by the DGCL.

We have entered into indemnification agreements with our directors and officers, whereby we have agreed to indemnify our directors and officers to the fullest extent permitted by law, including indemnification against expenses and liabilities incurred in legal proceedings to which the director or officer was, or is threatened to be made, a party by reason of the fact that such director or officer is or was a director, officer, employee or agent of Twilio provided that such director or officer acted in good faith and in a manner that the director or officer reasonably believed to be in, or not opposed to, the best interest of Twilio.

We maintain insurance policies that indemnify our directors and officers against various liabilities arising under the Securities Act and the Exchange Act, that might be incurred by any director or officer in his or her capacity as such.

Item 16. Exhibits

II-1

Item 17. Undertakings

provided, however, that paragraphs (a)(1)(i), (a)(1)(ii) and (a)(1)(iii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the Commission by the registrant pursuant to Section 13 or Section 15(d) of the Securities Exchange Act of 1934 that are incorporated by reference in the registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of the registration statement.

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SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of San Francisco, State of California, on August 2, 2021.

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints Jeffrey Lawson, Khozema Shipchandler and Karyn Smith, and each of them, as his or her true and lawful attorney-in-fact and agent with full power of substitution and resubstitution, for such individual in any and all capacities, to sign any and all amendments to this Registration Statement (including post-effective amendments), and to file the same, with all exhibits thereto and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done in connection therewith, as fully for all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or any of them, or the individual’s substitute, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed by the following persons on behalf of the Company and in the capacities and on the dates indicated.

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Exhibit 5.1

August 2, 2021

Twilio Inc.

375 Beale Street, Suite 300

San Francisco, CA 94105

Ladies and Gentlemen:

At your request, we have examined the Registration Statement on Form S-3 (the “Registration Statement”) filed by Twilio Inc., a Delaware corporation (the “Company”), with the Securities and Exchange Commission (the “Commission”) on August 2, 2021, in connection with the registration for resale under the Securities Act of 1933, as amended (the “Securities Act”), of up to an aggregate of 1,175,923 shares of the Company’s Class A common stock, $0.001 par value per share (the “Common Stock”), issued and outstanding and to be sold by certain selling stockholders (the “Selling Stockholders”) in connection with that certain Agreement and Plan of Merger dated as of May 16, 2021 by and among the Company, certain wholly owned subsidiaries of the Company, Zipwhip, Inc. and Fortis Advisors LLC, solely in its capacity as the Selling Stockholders’ agent.

In connection with our opinion expressed below we such matters of fact as we have deemed necessary in order to render the opinion set forth herein, which included examination of the following:

In our examination of documents for purposes of this opinion, we have assumed, and express no opinion as to, the authenticity and completeness of all documents submitted to us as originals, the conformity to originals and completeness of all documents submitted to us as copies, the legal capacity of all persons or entities executing the same (other than the Company), the lack of any undisclosed termination, modification, waiver or amendment to any document reviewed by us and the due authorization, execution and delivery of all such documents by the selling stockholders where due authorization, execution and delivery are prerequisites to the effectiveness thereof. The Company’s capital stock is uncertificated. We assume that the issued Stock will not be reissued by the Company in uncertificated form until any previously issued stock certificate representing such issued Stock have been surrendered to the Company in accordance with DGCL Section 158 and that the Company will properly register the transfer of the Stock to the purchasers of such Stock on the Company’s record of uncertificated securities.

We render this opinion only with respect to, and express no opinion herein concerning the application or effect of the laws of any jurisdiction other than, the existing laws of the United States of America and of the Delaware General Corporation Law.

Twilio Inc.

Page 2

August 2, 2021

With respect to our opinion expressed in paragraph (1) below as to the valid existence and good standing of the Company under the laws of the State of Delaware, we have relied solely upon the Certificate of Good Standing and representations made to us by the Company.

In connection with our opinion expressed in paragraphs (2) below, we have assumed that, at or prior to the time of the delivery of any shares of Stock, the Registration Statement will have been declared effective under the Securities Act of 1933, as amended, that the registration will apply to such shares of Stock and will not have been modified or rescinded and that there will not have occurred any change in law affecting the validity of the issuance of such shares of Stock.

This opinion is based upon the customary practice of lawyers who regularly give, and lawyers who regularly advise opinion recipients regarding, opinions of the kind set forth in this opinion letter, including customary practice as described in bar association reports.

In connection with our opinions expressed below, we have assumed that, (i) at or prior to the time of the issuance and delivery of any of the Common Stock by the Company to the Selling Stockholders and as of the date hereof, there will not have occurred any change in the law or the facts affecting the validity of the Common Stock, any change in actions of the Board or the Company’s stockholders, or any amendments to the Charter Documents, and (ii) at the time of the issuance and as of the date hereof, no stop order suspending the Registration Statement’s effectiveness will have been issued and remain in effect, and that the Registration Statement will not have been modified or rescinded. We also have assumed that the issuance and delivery of the Shares by the Company to the Selling Stockholders, immediately prior to the rendition of this opinion, is in compliance by the Company with the terms of the Common Stock and will not result in a violation of any provision of any of the Charter Documents or of any instrument or agreement then binding upon the Company or any restriction imposed by any court or governmental body then having jurisdiction over the Company.

Based upon the foregoing, we are of the opinion that:

We consent to the use of this opinion as an exhibit to the Registration Statement and further consent to all references to us, if any, in the Registration Statement, the prospectus constituting a part thereof and any amendments thereto.

This opinion is intended solely for use in connection with issuance and sale of the Selling Stockholders’ Shares subject to the Registration Statement and is not to be relied upon for any other purpose. This opinion is rendered on, and speaks only as of, the date first written above, based solely on our understanding of facts in existence as of such date after the aforementioned examination. We assume no obligation to advise you of any fact, circumstance, event or change in the law or the facts that may hereafter be brought to our attention, whether or not such occurrence would affect or modify any of the opinions expressed herein.

Very truly yours,

/s/ Fenwick & West LLP

FENWICK & WEST LLP

Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

The Board of Directors

Twilio Inc.:

We consent to the use of our reports dated February 25, 2021, with respect to the consolidated balance sheets of Twilio Inc. as of December 31, 2020 and 2019, the related consolidated statements of operations, comprehensive loss, stockholders’ equity, and cash flows for each of the years in the three-year period ended December 31, 2020, and the related notes (collectively, the “consolidated financial statements”), and the effectiveness of internal control over financial reporting as of December 31, 2020, incorporated herein by reference and to the reference to our firm under the heading “Experts” in the prospectus.

The audit report on the effectiveness of internal control over financial reporting as of December 31, 2020, contains an explanatory paragraph that states that the Company acquired Segment.io (Segment) during fiscal 2020, and management excluded from its assessment of the effectiveness of the Company’s internal control over financial reporting as of December 1, 2020, Segment’s internal control over financial reporting associated with $253.6 million, or 3%, of total assets and $23.0 million, or 1% of total revenues included in the consolidated financial statements of the Company as of and for the year ended December 31, 2020. Our audit of internal control over financial reporting of the Company also excluded an evaluation of the internal control over financial reporting of Segment.

Our report on the consolidated financial statements refers to the change in method of accounting for leases on the adoption of Financial Accounting Standards Board’s Accounting Standards Codification (ASC) Topic 842, Leases, as of January 1, 2019.

/s/ KPMG LLP

Santa Clara, California

August 2, 2021