Statement of Changes in Beneficial Ownership - Form 4

Ownership Submission

FORM 4 Check this box if no longer subject to Section 16, Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person * Third Rock Ventures V, L.P. 2. Issuer Name and Ticker or Trading Symbol Septerna, Inc. [SEPN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O THIRD ROCK VENTURES, LLC , 201 BROOKLINE AVE, SUITE 1401 3. Date of Earliest Transaction (Month/Day/Year) (Street) BOSTON MA 02215 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Join/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code 4. Securities Acquired (A) or Disposed of (D) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) 6. Ownership Form: Direct (D) or Indirect (I) 7. Nature of Indirect Beneficial Ownership Code V Amount (A) or (D) Price

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivate Security	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code	5. Number of Derivative Securities Acquired (A) or Disposed of (D)	6. Date Exercisable and Expiration Date	7. Title and Amount of Securities Underlying Derivative Security	8. Price of Derivative Security	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s)	10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)	11. Nature of Indirect Beneficial Ownership
Code	V	(A)	(D)	Date Exercisable	Expriation Date	Title	Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address	Relationships
Director	10% Owner	Officer	Other
Third Rock Ventures V, L.P. C/O THIRD ROCK VENTURES, LLC 201 BROOKLINE AVE, SUITE 1401 BOSTON, MA02215
Third Rock Ventures GP V, LP C/O THIRD ROCK VENTURES, LLC 201 BROOKLINE AVE, SUITE 1401 BOSTON, MA02215
TRV GP V, LLC C/O THIRD ROCK VENTURES, LLC 201 BROOKLINE AVE, SUITE 1401 BOSTON, MA02215
Third Rock Ventures VI, L.P. C/O THIRD ROCK VENTURES, LLC 201 BROOKLINE AVE, SUITE 1401 BOSTON, MA02215
Third Rock Ventures GP VI, L.P. C/O THIRD ROCK VENTURES, LLC 201 BROOKLINE AVE, SUITE 1401 BOSTON, MA02215
TRV GP VI, LLC C/O THIRD ROCK VENTURES, LLC 201 BROOKLINE AVE, SUITE 1401 BOSTON, MA02215

Signatures

/s/ Kevin Gillis, Chief Operating Officer of TRV GP V, LLC, general partner of Third Rock Ventures GP V, L.P., general partner of Third Rock Ventures V, L.P.	2024-10-28
**Signature of Reporting Person	Date
/s/ Kevin Gillis, Chief Operating Officer of TRV GP V, LLC, general partner of Third Rock Ventures GP V, L.P.	2024-10-28
**Signature of Reporting Person	Date
/s/ Kevin Gillis, Chief Operating Officer of TRV GP V, LLC	2024-10-28
**Signature of Reporting Person	Date
/s/ Kevin Gillis, Chief Operating Officer of TRV GP VI, LLC, general partner of Third Rock Ventures GP VI, L.P., general partner of Third Rock Ventures VI, L.P.	2024-10-28
**Signature of Reporting Person	Date
/s/ Kevin Gillis, Chief Operating Officer of TRV GP VI, LLC, general partner of Third Rock Ventures GP VI, L.P.	2024-10-28
**Signature of Reporting Person	Date
/s/ Kevin Gillis, Chief Operating Officer of TRV GP VI, LLC	2024-10-28
**Signature of Reporting Person	Date

Explanation of Responses:

(*)	If the form is filed by more than one reporting person, see Instruction 5(b)(v).
(**)	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Upon the closing of the Issuer's initial public offering, each share of Series A Preferred Stock and Series B Preferred Stock (collectively, the "Preferred Stock") automatically converted into Common Stock on a one-for-8.6103 basis without payment of consideration. The Preferred Stock had no expiration date.
(2)	The shares are held directly by Third Rock Ventures V, L.P. ("TRV V"). The general partner of TRV V is Third Rock Ventures GP V, L.P. ("TRV GP V"). The general partner of TRV GP V is TRV GP V, LLC ("TRV GP V LLC"). Each of TRV GP V, and TRV GP V LLC, disclaims beneficial ownership of these shares except to the extent of its pecuniary interest therein, if any, and this report shall not be deemed an admission that it is the beneficial owner of such shares.
(3)	The shares are held directly by Third Rock Ventures VI, L.P. ("TRV VI"). The general partner of TRV VI is Third Rock Ventures GP VI, L.P. ("TRV GP VI"). The general partner of TRV GP VI is TRV GP VI, LLC ("TRV GP VI LLC"). Each of TRV GP VI, and TRV GP VI LLC, disclaims beneficial ownership of these shares except to the extent of its pecuniary interest therein, if any, and this report shall not be deemed an admission that it is the beneficial owner of such shares.
(4)	Each of Reporting Persons disclaims the existence of a Section 13(d) "group" as between the TRV V related parties and the TRV VI related parties and this report shall not be deemed an admission that any of such parties is or may be part of such a group with any of the other parties.

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