STOCK TITAN
  1. Home
  2. Sec-filings
  3. SEPN
  4. [Form 4] Septerna, Inc. Insider Trading Activity

Form 4: Third Rock Ventures reports acquisition/exercise transactions in SEPN

Filing Impact
(Very High)
Filing Sentiment
(Very Negative)
Form Type
4

Rhea-AI Filing Summary

Third Rock Ventures V, L.P. reported acquisition or exercise transactions in a Form 4 filing for SEPN. The filing lists transactions totaling 147,200 shares at a weighted average price of $50.27 per share from August 12, 2026 to August 12, 2026.

Positive

  • None.

Negative

  • None.

Insights

Analyzing...

Insider Third Rock Ventures V, L.P., Third Rock Ventures GP V, LP, TRV GP V, LLC, Third Rock Ventures VI, L.P., Third Rock Ventures GP VI, L.P., TRV GP VI, LLC
Role 10% Owner | 10% Owner | 10% Owner | 10% Owner | 10% Owner | 10% Owner
Sold 147,200 shs ($7.40M)
Type Security Shares Price Value
Sale Common Stock F1, F2, F3 147,059 $50.27 $7.39M
Sale Common Stock F1, F4, F3 141 $51.08 $7K
holding Common Stock F5 -- -- --
Holdings After Transaction: Common Stock — 6,068,391 shares (Direct); Common Stock — 4,211,659 shares (Indirect, By Third Rock Ventures VI, L.P.)
Footnotes (5)
  1. F1. The reported transactions were effected pursuant to a Rule 10b5-1 trading plan dated March 26, 2026, previously adopted by the Reporting Person.
  2. F2. The price reported is a weighted average price. These shares were sold in multiple transactions at prices ranging from $50.05 to $50.81, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (2).
  3. F3. These shares are directly held 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 the 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. F4. The price reported is a weighted average price. These shares were sold in multiple transactions at prices ranging from $51.00 to $51.10, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (4).
  5. F5. 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. Each of Reporting Persons disclaims the existence of a Section 13(d) "group" as between any TRV V related parties and any 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.
Shares sold (block 1) 147,059 shares Open-market sale of Septerna common stock at weighted average price on August 12, 2026
Weighted average price (block 1) $50.27 per share First sale block, trades ranged from $50.05 to $50.81
Price range (block 1) $50.05–$50.81 Individual trade prices for 147,059-share sale block
Shares sold (block 2) 141 shares Additional open-market sale of Septerna common stock on August 12, 2026
Weighted average price (block 2) $51.08 per share Second sale block, trades ranged from $51.00 to $51.10
Price range (block 2) $51.00–$51.10 Individual trade prices for 141-share sale block
Indirect holdings 4,211,659 shares Septerna common stock held indirectly by Third Rock Ventures VI, L.P.
Rule 10b5-1 trading plan regulatory
"reported transactions were effected pursuant to a Rule 10b5-1 trading plan"
A Rule 10b5-1 trading plan is a pre-arranged schedule that allows company insiders to buy or sell stock at specific times, even if they have inside information. It helps prevent accusations of unfair trading by making these transactions look planned and transparent, rather than sneaky or illegal.
weighted average price financial
"The price reported is a weighted average price. These shares were sold"
Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.
pecuniary interest financial
"disclaims beneficial ownership of the shares except to the extent of its pecuniary interest"
Section 13(d) "group" regulatory
"disclaims the existence of a Section 13(d) "group" as between any TRV V related"

FAQ

What insider transactions in SEPN did Third Rock Ventures report on August 12, 2026?
Third Rock Ventures V, L.P. reported two open-market sales of Septerna (SEPN) common stock on August 12, 2026, totaling 147,200 shares across trades executed at weighted average prices near $50–$51 per share.

How many Septerna (SEPN) shares did Third Rock Ventures sell and at what prices?
Third Rock Ventures V, L.P. sold 147,059 SEPN shares at a weighted average of $50.27 and 141 shares at a weighted average of $51.08, with individual trades ranging from $50.05–$50.81 and $51.00–$51.10 respectively.

Was the SEPN insider sale by Third Rock Ventures done under a Rule 10b5-1 plan?
Yes. The reported SEPN transactions were effected pursuant to a Rule 10b5-1 trading plan dated March 26, 2026, previously adopted by the reporting person, and the Form 4 affirms use of a Rule 10b5-1 plan.

How many Septerna (SEPN) shares does Third Rock Ventures VI, L.P. hold after these transactions?
The report lists an indirect holding of 4,211,659 SEPN common shares held by Third Rock Ventures VI, L.P.. Its general partners TRV GP VI, L.P. and TRV GP VI, LLC disclaim beneficial ownership beyond their pecuniary interests.

Who actually holds the SEPN shares involved in Third Rock Ventures’ Form 4?
The sold shares are held directly by Third Rock Ventures V, L.P., whose general partners are Third Rock Ventures GP V, L.P. and TRV GP V, LLC. The large remaining block is held by Third Rock Ventures VI, L.P. through its own general partners.

Do the Third Rock Ventures entities claim to be a Section 13(d) group in SEPN?
No. The reporting persons state that TRV VI-related entities and TRV V-related entities each disclaim the existence of a Section 13(d) “group” with one another and do not admit to being part of such a group.

AI-generated analysis. How Rhea-AI works. Not financial advice.

See more from StockTitan in Google Search and AI answers. Adds StockTitan as a preferred source · opens Google
Add on Google
Form 4 Insider Transactions: What Each Field Means →
SEC Form 4
FORM 4UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940
OMB APPROVAL
OMB Number:3235-0287
Estimated average burden
hours per response:0.5
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
X
Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.
1. Name and Address of Reporting Person*
Third Rock Ventures V, L.P.
(Last)(First)(Middle)
C/O THIRD ROCK VENTURES, LLC
201 BROOKLINE AVE, SUITE 1401
(Street)
BOSTON MASSACHUSETTS 02215
(City)(State)(Zip)
UNITED STATES
(Country)		2. Issuer Name and Ticker or Trading Symbol
Septerna, Inc. [ SEPN ] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
DirectorX10% Owner
Officer (give title below)Other (specify below)
2a. Foreign Trading Symbol
3. Date of Earliest Transaction (Month/Day/Year)
08/12/2026		6. Individual or Joint/Group Filing (Check Applicable Line)
Form filed by One Reporting Person
XForm filed by More than One Reporting Person
4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year)2A. Deemed Execution Date, if any (Month/Day/Year)3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4)
CodeVAmount(A) or (D)Price
Common Stock08/12/2026S(1)147,059A$50.27(2)6,068,532D(3)
Common Stock08/12/2026S(1)141A$51.08(4)6,068,391D(3)
Common Stock4,211,659IBy Third Rock Ventures VI, L.P.(5)
Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3) 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 (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 6. Date Exercisable and Expiration Date (Month/Day/Year)7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4)
CodeV(A)(D)Date ExercisableExpiration DateTitleAmount or Number of Shares
1. Name and Address of Reporting Person*
Third Rock Ventures V, L.P.
(Last)(First)(Middle)
C/O THIRD ROCK VENTURES, LLC
201 BROOKLINE AVE, SUITE 1401
(Street)
BOSTON MASSACHUSETTS 02215
(City)(State)(Zip)
UNITED STATES
(Country)
Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
Third Rock Ventures GP V, LP
(Last)(First)(Middle)
201 BROOKLINE AVE, SUITE 1401
(Street)
BOSTON MASSACHUSETTS 02215
(City)(State)(Zip)
UNITED STATES
(Country)
Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
TRV GP V, LLC
(Last)(First)(Middle)
201 BROOKLINE AVE, SUITE 1401
(Street)
BOSTON MASSACHUSETTS 02215
(City)(State)(Zip)
UNITED STATES
(Country)
Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
Third Rock Ventures VI, L.P.
(Last)(First)(Middle)
C/O THIRD ROCK VENTURES, LLC
201 BROOKLINE AVE, SUITE 1401
(Street)
BOSTON MASSACHUSETTS 02215
(City)(State)(Zip)
UNITED STATES
(Country)
Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
Third Rock Ventures GP VI, L.P.
(Last)(First)(Middle)
201 BROOKLINE AVE, SUITE 1401
(Street)
BOSTON MASSACHUSETTS 02215
(City)(State)(Zip)
UNITED STATES
(Country)
Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
1. Name and Address of Reporting Person*
TRV GP VI, LLC
(Last)(First)(Middle)
201 BROOKLINE AVE, SUITE 1401
(Street)
BOSTON MASSACHUSETTS 02215
(City)(State)(Zip)
UNITED STATES
(Country)
Relationship of Reporting Person(s) to Issuer
DirectorX10% Owner
Officer (give title below)Other (specify below)
Explanation of Responses:
1. The reported transactions were effected pursuant to a Rule 10b5-1 trading plan dated March 26, 2026, previously adopted by the Reporting Person.
2. The price reported is a weighted average price. These shares were sold in multiple transactions at prices ranging from $50.05 to $50.81, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (2).
3. These shares are directly held 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 the 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. The price reported is a weighted average price. These shares were sold in multiple transactions at prices ranging from $51.00 to $51.10, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (4).
5. 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. Each of Reporting Persons disclaims the existence of a Section 13(d) "group" as between any TRV V related parties and any 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.
/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.08/14/2026
/s/ Kevin Gillis, Chief Operating Officer of TRV GP V, LLC, general partner of Third Rock Ventures GP V, L.P.08/14/2026
/s/ Kevin Gillis, Chief Operating Officer of TRV GP V, LLC08/14/2026
/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.08/14/2026
/s/ Kevin Gillis, Chief Operating Officer of TRV GP VI, LLC, general partner of Third Rock Ventures GP VI, L.P.08/14/2026
/s/ Kevin Gillis, Chief Operating Officer of TRV GP VI, LLC08/14/2026
** Signature of Reporting PersonDate
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)

Source: View Original Filing on SEC EDGAR