<SEC-DOCUMENT>0001447669-21-000078.txt : 20210301
<SEC-HEADER>0001447669-21-000078.hdr.sgml : 20210301
<ACCEPTANCE-DATETIME>20210301183655
ACCESSION NUMBER:		0001447669-21-000078
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20210225
FILED AS OF DATE:		20210301
DATE AS OF CHANGE:		20210301

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Hu George
		CENTRAL INDEX KEY:			0001386396

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-37806
		FILM NUMBER:		21700327

	MAIL ADDRESS:	
		STREET 1:		C/O SALESFORCE.COM
		STREET 2:		1 MARKET STREET, SUITE 300
		CITY:			SAN FRANCISCO
		STATE:			CA
		ZIP:			94105

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TWILIO INC
		CENTRAL INDEX KEY:			0001447669
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-PREPACKAGED SOFTWARE [7372]
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		375 BEALE ST
		STREET 2:		SUITE 300
		CITY:			San Francisco
		STATE:			CA
		ZIP:			94105
		BUSINESS PHONE:		650-270-2199

	MAIL ADDRESS:	
		STREET 1:		375 BEALE ST
		STREET 2:		SUITE 300
		CITY:			San Francisco
		STATE:			CA
		ZIP:			94105
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_161464179215862.xml
<DESCRIPTION>FORM 4
<TEXT>
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    <periodOfReport>2021-02-25</periodOfReport>

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    <issuer>
        <issuerCik>0001447669</issuerCik>
        <issuerName>TWILIO INC</issuerName>
        <issuerTradingSymbol>TWLO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001386396</rptOwnerCik>
            <rptOwnerName>Hu George</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TWILIO INC.</rptOwnerStreet1>
            <rptOwnerStreet2>101 SPEAR STREET, FIRST FLOOR</rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94105</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Operating Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-02-25</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionAmounts>
                <transactionShares>
                    <value>9742</value>
                    <footnoteId id="F1"/>
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                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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                    <value>D</value>
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    <derivativeTable>
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                </transactionShares>
                <transactionPricePerShare>
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            <exerciseDate>
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            <expirationDate>
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                <underlyingSecurityTitle>
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            <exerciseDate>
                <footnoteId id="F4"/>
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            <expirationDate>
                <value>2030-02-21</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>58559.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
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            <expirationDate>
                <value>2028-02-19</value>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>96214.0</value>
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                <sharesOwnedFollowingTransaction>
                    <value>96214</value>
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                    <value>D</value>
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            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
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                <footnoteId id="F6"/>
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            <expirationDate>
                <value>2024-02-27</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>185000.0</value>
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                <sharesOwnedFollowingTransaction>
                    <value>185000</value>
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                    <value>D</value>
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                <value>Employee Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>31.72</value>
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            <exerciseDate>
                <footnoteId id="F7"/>
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            <expirationDate>
                <value>2024-02-27</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>185000.0</value>
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            </underlyingSecurity>
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                <sharesOwnedFollowingTransaction>
                    <value>185000</value>
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                    <value>D</value>
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        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>111.32</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F8"/>
            </exerciseDate>
            <expirationDate>
                <value>2029-01-30</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>73798.0</value>
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        </derivativeHolding>
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            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>31.72</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F9"/>
            </exerciseDate>
            <expirationDate>
                <value>2024-02-27</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>29782.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>29782</value>
                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
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        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>31.72</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F10"/>
            </exerciseDate>
            <expirationDate>
                <value>2024-02-27</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>185000.0</value>
                </underlyingSecurityShares>
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                <sharesOwnedFollowingTransaction>
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                <directOrIndirectOwnership>
                    <value>D</value>
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        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The shares reported in this transaction represent Restricted Stock Units (&quot;RSUs&quot;). Each RSU represents the contingent right to receive one share of the Issuer's Class A common stock. The RSUs shall vest as follows: 33% of the RSUs shall vest in equal quarterly installments between the first and second anniversaries of December 31, 2020, 33% of the RSUs shall vest in equal quarterly installments between the second and third anniversaries of December 31, 2020 and 34% of the RSUs shall vest in equal quarterly installments between the third and fourth anniversaries of December 31, 2020, subject to the Reporting Person's continued service to the Issuer through each vesting date.</footnote>
        <footnote id="F2">A portion of these shares represent RSUs. Each RSU represents a contingent right to receive one share of Issuer's Class A common stock.</footnote>
        <footnote id="F3">The shares subject to the stock option vest as follows: 33% of the stock option shall vest in equal quarterly installments between the first and second anniversaries of December 31, 2020, 33% of the stock option shall vest in equal quarterly installments between the second and third anniversaries of December 31, 2020 and 34% of the stock option shall vest in equal quarterly installments between the third and fourth anniversaries of December 31, 2020, subject to the Reporting Person's continued service to the Issuer through each vesting date.</footnote>
        <footnote id="F4">The shares subject to the stock option vest as follows: 33% of the stock option shall vest in equal quarterly installments between the first and second anniversaries of December 31, 2019, 33% of the stock option shall vest in equal quarterly installments between the second and third anniversaries of December 31, 2019 and 34% of the stock option shall vest in equal quarterly installments between the third and fourth anniversaries of December 31, 2019, subject to the Reporting Person's continued service to the Issuer through each vesting date.</footnote>
        <footnote id="F5">The shares subject to this option vest in 48 equal monthly installments, with the first installment on March 15, 2018, subject to the Reporting Person's continuous service to the Issuer through each vesting date.</footnote>
        <footnote id="F6">The shares subject to the stock option vest as follows: 50% of the stock option vested on March 31, 2018 and the remaining shares subject to the stock option shall vest in 24 equal monthly installments thereafter, subject to the Reporting Person's continued service to the Issuer through each vesting date.</footnote>
        <footnote id="F7">The shares subject to the stock option vest as follows: 50% of the stock option vested on June 30, 2019 and the remaining shares subject to the stock option shall vest in 24 equal monthly installments thereafter, subject to the Reporting Person's continued service to the Issuer through each vesting date.</footnote>
        <footnote id="F8">The stock option vests as follows: 33% of the stock option shall vest on December 31, 2020, 33% of the stock option shall vest on December 31, 2021 and 34% of the stock option shall vest on December 31, 2022, subject to the Reporting Person's continued service to the Issuer through each vesting date.</footnote>
        <footnote id="F9">The shares subject to the stock option vest as follows: 25% of the stock option vested on February 28, 2018 and the remaining shares subject to the stock option shall vest in equal monthly installments over the following three years, subject to the Reporting Person's continued service to the Issuer through each vesting date.</footnote>
        <footnote id="F10">The shares subject to the stock option vest as follows: 50% of the stock option vested on December 31, 2018 and the remaining shares subject to the stock option shall vest in 24 equal monthly installments thereafter, subject to the Reporting Person's continued service to the Issuer through each vesting date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Karyn Smith as attorney in fact for Reporting Person</signatureName>
        <signatureDate>2021-03-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
