Septerna (SEPN): RA Capital funds disclose sale of 1.49M common shares

Rhea-AI Filing Summary

RA Capital–affiliated entities reported open-market sales of Septerna, Inc. common stock. On 2026-08-12, RA Capital Healthcare Fund LP and RA Capital Nexus Fund III, L.P. each sold 746,500 shares of Septerna common stock at $42.50 per share, for total reported sales of 1,493,000 shares. The positions are reported as indirectly owned, with RA Capital Management, L.P., its general partner, and principals Peter Kolchinsky and Rajeev Shah disclaiming beneficial ownership beyond their respective pecuniary interests.

Insider Trade Summary

Net Seller: 1,493,000 shares

Net Sell 2 txns

Insider RA CAPITAL MANAGEMENT, L.P., RA Capital Healthcare Fund LP, RA Capital Nexus Fund III, L.P., Kolchinsky Peter, Shah Rajeev M.

Role Director, 10% Owner | Director, 10% Owner | Director | Director, 10% Owner | Director, 10% Owner

Sold 1,493,000 shs ($63.45M)

Type	Security	Shares	Price	Value
Sale	Common Stock F1, F2	746,500	$42.50	$31.73M
Sale	Common Stock F1, F3	746,500	$42.50	$31.73M

Holdings After Transaction: Common Stock — 725,443 shares (Indirect, See footnotes)

Footnotes (3)

1. F1. RA Capital Management, L.P. (the "Adviser") is the investment manager for RA Capital Healthcare Fund, L.P. (the "Fund") and RA Capital Nexus Fund III, L.P. (the "Nexus Fund III"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. Each of the Adviser, the Adviser GP, the Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaims beneficial ownership of any of the reported securities, except to the extent of its or his respective pecuniary interest therein.
2. F2. Held directly by the Fund.
3. F3. Held directly by the Nexus Fund III.

Key Figures

Shares sold by RA Capital Healthcare Fund LP: 746,500 shares Shares sold by RA Capital Nexus Fund III, L.P.: 746,500 shares Total shares sold by RA Capital–affiliated entities: 1,493,000 shares +1 more

4 metrics

Shares sold by RA Capital Healthcare Fund LP 746,500 shares Sale of Septerna common stock on 2026-08-12

Shares sold by RA Capital Nexus Fund III, L.P. 746,500 shares Sale of Septerna common stock on 2026-08-12

Total shares sold by RA Capital–affiliated entities 1,493,000 shares Combined reported sales of Septerna common stock on 2026-08-12

Sale price per share $42.50 Per-share price for each reported common stock sale

Key Terms

beneficial ownership, pecuniary interest, indirectly owned, investment manager

4 terms

beneficial ownership financial

"disclaims beneficial ownership of any of the reported securities"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

pecuniary interest financial

"except to the extent of its or his respective pecuniary interest"

indirectly owned financial

"The positions are reported as indirectly owned, with RA Capital"

investment manager financial

"RA Capital Management, L.P. (the "Adviser") is the investment manager"

FAQ

What insider transactions did SEPN report by RA Capital on this Form 4?

The Form 4 reports that RA Capital Healthcare Fund LP and RA Capital Nexus Fund III, L.P. each sold 746,500 Septerna (SEPN) common shares on 2026-08-12, for combined reported sales of 1,493,000 shares at $42.50 per share.

At what price were the Septerna (SEPN) shares sold by RA Capital entities?

Both reported sales of Septerna (SEPN) common stock were executed at $42.50 per share. The filing identifies these as sales of non-derivative common shares in open-market or private transactions at this per-share price.

How many Septerna (SEPN) shares did each RA Capital fund sell?

RA Capital Healthcare Fund LP and RA Capital Nexus Fund III, L.P. each sold 746,500 Septerna (SEPN) common shares. Together, these related entities reported total sales of 1,493,000 shares on the same transaction date, 2026-08-12.

Are the Septerna (SEPN) shares held directly or indirectly by the reporting persons?

The reported Septerna (SEPN) holdings are shown as indirectly owned. Footnotes explain the shares are held directly by the Fund and Nexus Fund III, with RA Capital Management, L.P. and related parties disclaiming beneficial ownership beyond pecuniary interests.

Did the RA Capital Septerna (SEPN) trades occur under a Rule 10b5-1 plan?

The filing’s Rule 10b5-1 checkbox is not marked as affirming a trading plan. There is no footnote indicating that the Septerna (SEPN) sales were executed pursuant to a pre-arranged Rule 10b5-1 trading plan.

Who is associated with RA Capital’s board representation at Septerna (SEPN)?

The filing notes that Jake Simson, a Partner of the Adviser (RA Capital Management, L.P.), serves on Septerna’s board of directors. This indicates board representation linked to the RA Capital advisory organization.

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 Not now

Form 4 Insider Transactions: What Each Field Means →

Available on EDGAR 08/14/2026 - 05:12 PM Accepted by SEC EDGAR 08/14/2026 - 05:11 PM Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED 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).

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^*

RA CAPITAL MANAGEMENT, L.P.

(Last) (First) (Middle)

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(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)

X	Director	X	10% 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
X	Form 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)
			Code	V	Amount	(A) or (D)	Price
Common Stock	08/12/2026		S		746,500	D	$42.5	4,777,415	I	See footnotes(1)(2)
Common Stock	08/12/2026		S		746,500	D	$42.5	725,443	I	See footnotes(1)(3)

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)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

1. Name and Address of Reporting Person^*

RA CAPITAL MANAGEMENT, L.P.

(Last) (First) (Middle)

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

RA Capital Healthcare Fund LP

(Last) (First) (Middle)

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

RA Capital Nexus Fund III, L.P.

(Last) (First) (Middle)

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

Kolchinsky Peter

(Last) (First) (Middle)

C/O RA CAPITAL MANAGEMENT, L.P.

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

Shah Rajeev M.

(Last) (First) (Middle)

C/O RA CAPITAL MANAGEMENT, L.P.

200 BERKELEY STREET, 18TH FLOOR

(Street)

BOSTON MASSACHUSETTS 02116

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

Explanation of Responses:

1. RA Capital Management, L.P. (the "Adviser") is the investment manager for RA Capital Healthcare Fund, L.P. (the "Fund") and RA Capital Nexus Fund III, L.P. (the "Nexus Fund III"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. Each of the Adviser, the Adviser GP, the Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaims beneficial ownership of any of the reported securities, except to the extent of its or his respective pecuniary interest therein.

2. Held directly by the Fund.

3. Held directly by the Nexus Fund III.

Remarks:

Jake Simson, a Partner of the Adviser, serves on the Issuer's board of directors.

	/s/ Peter Kolchinsky, Manager of RA Capital Management, L.P.	08/14/2026
	/s/ Peter Kolchinsky, Manager of RA Capital Healthcare Fund GP, LLC, the General Partner of RA Capital Healthcare Fund, L.P.	08/14/2026
	/s/ Peter Kolchinsky, Manager of RA Capital Nexus Fund III GP, LLC, the General Partner of RA Capital Nexus Fund III, L.P.	08/14/2026
	/s/ Peter Kolchinsky, individually	08/14/2026
	/s/ Rajeev Shah, individually	08/14/2026
	** Signature of Reporting Person	Date
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)