<SEC-DOCUMENT>0001447669-22-000124.txt : 20220623
<SEC-HEADER>0001447669-22-000124.hdr.sgml : 20220623
<ACCEPTANCE-DATETIME>20220623162601
ACCESSION NUMBER:		0001447669-22-000124
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20220621
FILED AS OF DATE:		20220623
DATE AS OF CHANGE:		20220623

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			DONIO ELENA A.
		CENTRAL INDEX KEY:			0001219068
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0930

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-37806
		FILM NUMBER:		221035815

	MAIL ADDRESS:	
		STREET 1:		C/O CONCUR TECHNOLOGIES, INC.
		STREET 2:		18400 NE UNION HILL RD.
		CITY:			REDMOND
		STATE:			WA
		ZIP:			98052

	FORMER NAME:	
		FORMER CONFORMED NAME:	DONIO ELENA A
		DATE OF NAME CHANGE:	20120112

	FORMER NAME:	
		FORMER CONFORMED NAME:	DONIO ELENA
		DATE OF NAME CHANGE:	20030214

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TWILIO INC
		CENTRAL INDEX KEY:			0001447669
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-PREPACKAGED SOFTWARE [7372]
		IRS NUMBER:				262574840
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		101 SPEAR STREET
		STREET 2:		FIRST FLOOR
		CITY:			San Francisco
		STATE:			CA
		ZIP:			94105
		BUSINESS PHONE:		415-390-2337

	MAIL ADDRESS:	
		STREET 1:		101 SPEAR STREET
		STREET 2:		FIRST FLOOR
		CITY:			San Francisco
		STATE:			CA
		ZIP:			94105
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_165601594752026.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2022-06-21</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001219068</rptOwnerCik>
            <rptOwnerName>DONIO ELENA A.</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>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President of Revenue</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2022-06-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>298162</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>310616</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>85.17</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2022-06-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>167150</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2032-06-20</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>167150.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>167150</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeHolding>
            <securityTitle>
                <value>Class B Common Stock</value>
                <footnoteId id="F4"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F4"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>18252.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18252</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </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 vest as follows: 1/16 of the RSUs shall vest on the three month anniversary of the Vesting Commencement Date of May 15, 2022, and 1/16 of the RSUs shall vest each quarter thereafter on February 15, May 15, August 15 and November 15, as applicable for the next 15 quarters, 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 option shall vest in 48 equal monthly installments over the following four years beginning one month following the Transaction Date, subject to the Reporting Person's continued service to the Issuer through each vesting date.</footnote>
        <footnote id="F4">Each share of Class B common stock is convertible into one share of Class A common stock at the option of the holder and has no expiration date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Sarah DiLorenzo as attorney in fact for Reporting Person</signatureName>
        <signatureDate>2022-06-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
