<SEC-DOCUMENT>0000950170-25-019900.txt : 20250213
<SEC-HEADER>0000950170-25-019900.hdr.sgml : 20250213
<ACCEPTANCE-DATETIME>20250213161502
ACCESSION NUMBER:		0000950170-25-019900
CONFORMED SUBMISSION TYPE:	SCHEDULE 13G
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20250213
DATE AS OF CHANGE:		20250213

SUBJECT COMPANY:	

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Septerna, Inc.
		CENTRAL INDEX KEY:			0001984086
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		ORGANIZATION NAME:           	03 Life Sciences
		IRS NUMBER:				843891440
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SCHEDULE 13G
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	005-94678
		FILM NUMBER:		25620444

	BUSINESS ADDRESS:	
		STREET 1:		250 EAST GRAND AVENUE, SUITE 65
		CITY:			SOUTH SAN FRANCISCO
		STATE:			CA
		ZIP:			94080
		BUSINESS PHONE:		650-338-3533

	MAIL ADDRESS:	
		STREET 1:		250 EAST GRAND AVENUE, SUITE 65
		CITY:			SOUTH SAN FRANCISCO
		STATE:			CA
		ZIP:			94080

FILED BY:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Third Rock Ventures V, L.P.
		CENTRAL INDEX KEY:			0001778071
		ORGANIZATION NAME:           	
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SCHEDULE 13G

	BUSINESS ADDRESS:	
		STREET 1:		29 NEWBURY STREET, 3RD FLOOR
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
		BUSINESS PHONE:		617-585-2000

	MAIL ADDRESS:	
		STREET 1:		29 NEWBURY STREET, 3RD FLOOR
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
</SEC-HEADER>
<DOCUMENT>
<TYPE>SCHEDULE 13G
<SEQUENCE>1
<FILENAME>primary_doc.xml
<TEXT>
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    <submissionType>SCHEDULE 13G</submissionType>
    <filerInfo>
      <filer>
        <filerCredentials>
          <cik>0001778071</cik>
          <ccc>XXXXXXXX</ccc>
        </filerCredentials>
      </filer>
      <liveTestFlag>LIVE</liveTestFlag>



    </filerInfo>
  </headerData>
  <formData>
    <coverPageHeader>
      <securitiesClassTitle>Common Stock, $0.001 par value per share</securitiesClassTitle>
      <eventDateRequiresFilingThisStatement>12/31/2024</eventDateRequiresFilingThisStatement>
      <issuerInfo>
        <issuerCik>0001984086</issuerCik>
        <issuerName>Septerna, Inc.</issuerName>
        <issuerCusip>81734D104</issuerCusip>
        <issuerPrincipalExecutiveOfficeAddress>
          <street1 xmlns="http://www.sec.gov/edgar/common">250 East Grand Avenue</street1>
          <street2 xmlns="http://www.sec.gov/edgar/common">Suite 65</street2>
          <city xmlns="http://www.sec.gov/edgar/common">South San Francisco</city>
          <stateOrCountry xmlns="http://www.sec.gov/edgar/common">CA</stateOrCountry>
          <zipCode xmlns="http://www.sec.gov/edgar/common">094080</zipCode>
        </issuerPrincipalExecutiveOfficeAddress>
      </issuerInfo>
      <designateRulesPursuantThisScheduleFiled>
        <designateRulePursuantThisScheduleFiled>Rule 13d-1(d)</designateRulePursuantThisScheduleFiled>
      </designateRulesPursuantThisScheduleFiled>
    </coverPageHeader>
    <coverPageHeaderReportingPersonDetails>


      <reportingPersonName>Third Rock Ventures V, L.P.</reportingPersonName>
      <memberGroup>b</memberGroup>
      <citizenshipOrOrganization>DE</citizenshipOrOrganization>
      <reportingPersonBeneficiallyOwnedNumberOfShares>
        <soleVotingPower>0</soleVotingPower>
        <sharedVotingPower>6215591</sharedVotingPower>
        <soleDispositivePower>0</soleDispositivePower>
        <sharedDispositivePower>6215591</sharedDispositivePower>
      </reportingPersonBeneficiallyOwnedNumberOfShares>
      <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>6215591</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>
      <aggregateAmountExcludesCertainSharesFlag>N</aggregateAmountExcludesCertainSharesFlag>
      <classPercent>14.0</classPercent>
      <typeOfReportingPerson>PN</typeOfReportingPerson>
    </coverPageHeaderReportingPersonDetails>
    <coverPageHeaderReportingPersonDetails>


      <reportingPersonName>Third Rock Ventures GP V, L.P.</reportingPersonName>
      <memberGroup>b</memberGroup>
      <citizenshipOrOrganization>DE</citizenshipOrOrganization>
      <reportingPersonBeneficiallyOwnedNumberOfShares>
        <soleVotingPower>0</soleVotingPower>
        <sharedVotingPower>6215591</sharedVotingPower>
        <soleDispositivePower>0</soleDispositivePower>
        <sharedDispositivePower>6215591</sharedDispositivePower>
      </reportingPersonBeneficiallyOwnedNumberOfShares>
      <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>6215591</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>
      <aggregateAmountExcludesCertainSharesFlag>N</aggregateAmountExcludesCertainSharesFlag>
      <classPercent>14.0</classPercent>
      <typeOfReportingPerson>PN</typeOfReportingPerson>
    </coverPageHeaderReportingPersonDetails>
    <coverPageHeaderReportingPersonDetails>


      <reportingPersonName>TRV GP V, LLC</reportingPersonName>
      <memberGroup>b</memberGroup>
      <citizenshipOrOrganization>DE</citizenshipOrOrganization>
      <reportingPersonBeneficiallyOwnedNumberOfShares>
        <soleVotingPower>0</soleVotingPower>
        <sharedVotingPower>6215591</sharedVotingPower>
        <soleDispositivePower>0</soleDispositivePower>
        <sharedDispositivePower>6215591</sharedDispositivePower>
      </reportingPersonBeneficiallyOwnedNumberOfShares>
      <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>6215591</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>
      <aggregateAmountExcludesCertainSharesFlag>N</aggregateAmountExcludesCertainSharesFlag>
      <classPercent>14.0</classPercent>
      <typeOfReportingPerson>OO</typeOfReportingPerson>
    </coverPageHeaderReportingPersonDetails>
    <coverPageHeaderReportingPersonDetails>


      <reportingPersonName>Third Rock Ventures VI, L.P.</reportingPersonName>
      <memberGroup>b</memberGroup>
      <citizenshipOrOrganization>DE</citizenshipOrOrganization>
      <reportingPersonBeneficiallyOwnedNumberOfShares>
        <soleVotingPower>0</soleVotingPower>
        <sharedVotingPower>3152456</sharedVotingPower>
        <soleDispositivePower>0</soleDispositivePower>
        <sharedDispositivePower>3152456</sharedDispositivePower>
      </reportingPersonBeneficiallyOwnedNumberOfShares>
      <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>3152456</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>
      <aggregateAmountExcludesCertainSharesFlag>N</aggregateAmountExcludesCertainSharesFlag>
      <classPercent>7.1</classPercent>
      <typeOfReportingPerson>PN</typeOfReportingPerson>
    </coverPageHeaderReportingPersonDetails>
    <coverPageHeaderReportingPersonDetails>


      <reportingPersonName>Third Rock Ventures GP VI, L.P.</reportingPersonName>
      <memberGroup>b</memberGroup>
      <citizenshipOrOrganization>DE</citizenshipOrOrganization>
      <reportingPersonBeneficiallyOwnedNumberOfShares>
        <soleVotingPower>0</soleVotingPower>
        <sharedVotingPower>3152456</sharedVotingPower>
        <soleDispositivePower>0</soleDispositivePower>
        <sharedDispositivePower>3152456</sharedDispositivePower>
      </reportingPersonBeneficiallyOwnedNumberOfShares>
      <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>3152456</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>
      <aggregateAmountExcludesCertainSharesFlag>N</aggregateAmountExcludesCertainSharesFlag>
      <classPercent>7.1</classPercent>
      <typeOfReportingPerson>PN</typeOfReportingPerson>
    </coverPageHeaderReportingPersonDetails>
    <coverPageHeaderReportingPersonDetails>


      <reportingPersonName>TRV GP VI, LLC</reportingPersonName>
      <memberGroup>b</memberGroup>
      <citizenshipOrOrganization>DE</citizenshipOrOrganization>
      <reportingPersonBeneficiallyOwnedNumberOfShares>
        <soleVotingPower>0</soleVotingPower>
        <sharedVotingPower>3152456</sharedVotingPower>
        <soleDispositivePower>0</soleDispositivePower>
        <sharedDispositivePower>3152456</sharedDispositivePower>
      </reportingPersonBeneficiallyOwnedNumberOfShares>
      <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>3152456</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>
      <aggregateAmountExcludesCertainSharesFlag>N</aggregateAmountExcludesCertainSharesFlag>
      <classPercent>7.1</classPercent>
      <typeOfReportingPerson>OO</typeOfReportingPerson>
    </coverPageHeaderReportingPersonDetails>
    <items>
      <item1>
        <issuerName>Septerna, Inc.</issuerName>
        <issuerPrincipalExecutiveOfficeAddress>250 East Grand AvenueSouth San Francisco, CA 94080</issuerPrincipalExecutiveOfficeAddress>
      </item1>
      <item2>
        <filingPersonName>(i) Third Rock Ventures V, L.P. ("TRV V");

(ii) Third Rock Ventures GP V, L.P. ("TRV GP V"), which is the sole general partner of TRV V;

(iii) TRV GP V, LLC ("TRV GP V LLC"), which is the sole general partner of TRV GP V;

(iv) Third Rock Ventures VI, L.P. ("TRV VI");

(v)  Third Rock Ventures GP VI, L.P. ("TRV GP VI"), which is the sole general partner of TRV VI; and

(vi) TRV GP VI, LLC ("TRV GP VI LLC"), which is the sole general partner of TRV GP VI.</filingPersonName>
        <principalBusinessOfficeOrResidenceAddress>The address of the principal business office of each of the Reporting Persons is Third Rock Ventures, LLC, 201 Brookline Ave, Suite 1401, Boston, MA 02215.</principalBusinessOfficeOrResidenceAddress>
        <citizenship>Each of TRV V, TRV GP V, TRV VI and TRV GP VI is a Delaware limited partnership.Each of TRV GP V LLC and TRV GP VI LLC is a Delaware limited liability company.</citizenship>
      </item2>
      <item3>
        <notApplicableFlag>Y</notApplicableFlag>
      </item3>
      <item4>
        <amountBeneficiallyOwned>(i) TRV V directly owns 6,215,591 shares of Common Stock (the "V Shares")
(ii) TRV GP V is the general partner of TRV V and may be deemed to beneficially own the V Shares.
(iii) TRV GP V LLC is the general partner of TRV GP V and may be deemed to beneficially own the V Shares.
(iv) TRV VI directly owns 3,152,456 shares of Common Stock (the "VI Shares").
(v)  TRV GP VI is the general partner of TRV VI and may be deemed to beneficially own the VI Shares.
(vi) TRV GP VI LLC is the general partner of TRV GP VI and may be deemed to beneficially own the VI Shares.

Each of TRV V, TRV GP V, and TRV GP V LLC, on the one hand, and TRV VI, TRV GP VI and TRV GP VI LLC, on the other hand, disclaim the existence of a "group" for purposes of Rule 13d-5 of the Securities Exchange Act of 1934, as amended, and nothing contained in this report shall be deemed an admission that any such group exists or may exist.</amountBeneficiallyOwned>
        <classPercent>The V shares represent approximately 14.0% of the outstanding shares of Common Stock.The VI shares represent approximately 7.1% of the outstanding shares of Common Stock.The percent of class was calculated based on 44,402,742 shares of common stock issued and outstanding as of November 11, 2024, as disclosed in the Issuer's 10-Q filed with the Securities and Exchange Commission on November 20, 2024.</classPercent>
        <numberOfSharesPersonHas>
          <solePowerOrDirectToVote>TRV V - 0
TRV GP V - 0
TRV GP V LLC - 0
TRV VI  - 0
TRV GP VI - 0
TRV GP VI LLC - 0</solePowerOrDirectToVote>
          <sharedPowerOrDirectToVote>TRV V - 6,215,591 shares
TRV GP V - 6,215,591 shares
TRV GP V LLC - 6,215,591 shares
TRV VI - 3,152,456 shares
TRV GP VI - 3,152,456 shares
TRV GP VI LLC - 3,152,456 shares</sharedPowerOrDirectToVote>
          <solePowerOrDirectToDispose>TRV V - 0
TRV GP V - 0
TRV GP V LLC - 0
TRV VI - 0
TRV GP VI - 0
TRV GP VI LLC - 0</solePowerOrDirectToDispose>
          <sharedPowerOrDirectToDispose>TRV V - 6,215,591 shares
TRV GP V - 6,215,591 shares
TRV GP V LLC - 6,215,591 shares
TRV VI - 3,152,456 shares
TRV GP VI - 3,152,456 shares
TRV GP VI LLC - 3,152,456 shares</sharedPowerOrDirectToDispose>
        </numberOfSharesPersonHas>
      </item4>
      <item5>
        <notApplicableFlag>Y</notApplicableFlag>
      </item5>
      <item6>
        <notApplicableFlag>Y</notApplicableFlag>
      </item6>
      <item7>
        <notApplicableFlag>Y</notApplicableFlag>
      </item7>
      <item8>
        <notApplicableFlag>Y</notApplicableFlag>
      </item8>
      <item9>
        <notApplicableFlag>Y</notApplicableFlag>
      </item9>
      <item10>
        <notApplicableFlag>Y</notApplicableFlag>
      </item10>
    </items>
    <signatureInformation>
      <reportingPersonName>Third Rock Ventures V, L.P.</reportingPersonName>
      <signatureDetails>
        <signature>/s/ Kevin Gillis</signature>
        <title>Kevin Gillis,COO of TRV GP V, LLC, general partner of Third Rock Ventures GP V, L.P., general partner of Third Rock Ventures V, L.P.</title>
        <date>02/13/2025</date>
      </signatureDetails>
    </signatureInformation>
    <signatureInformation>
      <reportingPersonName>Third Rock Ventures GP V, L.P.</reportingPersonName>
      <signatureDetails>
        <signature>/s/ Kevin Gillis</signature>
        <title>Kevin Gillis, COO of TRV GP VI, LLC, general partner of Third Rock Ventures GP VI, L.P</title>
        <date>02/13/2025</date>
      </signatureDetails>
    </signatureInformation>
    <signatureInformation>
      <reportingPersonName>TRV GP V, LLC</reportingPersonName>
      <signatureDetails>
        <signature>/s/ Kevin Gillis</signature>
        <title>Kevin Gillis, Chief Operating Officer of TRV GP V, LLC</title>
        <date>02/13/2025</date>
      </signatureDetails>
    </signatureInformation>
    <signatureInformation>
      <reportingPersonName>Third Rock Ventures VI, L.P.</reportingPersonName>
      <signatureDetails>
        <signature>/s/ Kevin Gillis</signature>
        <title>Kevin Gillis, COO of TRV GP VI, LLC, general partner of Third Rock Ventures GP VI, L.P., general partner of Third Rock Ventures VI, L.P.</title>
        <date>02/13/2025</date>
      </signatureDetails>
    </signatureInformation>
    <signatureInformation>
      <reportingPersonName>Third Rock Ventures GP VI, L.P.</reportingPersonName>
      <signatureDetails>
        <signature>/s/ Kevin Gillis</signature>
        <title>Kevin Gillis, Chief Operating Officer of TRV GP VI, LLC, general partner of Third Rock Ventures GP VI, L.P.</title>
        <date>02/13/2025</date>
      </signatureDetails>
    </signatureInformation>
    <signatureInformation>
      <reportingPersonName>TRV GP VI, LLC</reportingPersonName>
      <signatureDetails>
        <signature>/s/ Kevin Gillis</signature>
        <title>Kevin Gillis, Chief Operating Officer of TRV GP VI, LLC</title>
        <date>02/13/2025</date>
      </signatureDetails>
    </signatureInformation>
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</SEC-DOCUMENT>
