OrbiMed-linked entity sells Sionna shares at ~$44.6

Sionna Therapeutics director-affiliated entity records stock sales linked to OrbiMed funds.

Rhea-AI Filing Summary

Sionna Therapeutics director-affiliated entity records stock sales linked to OrbiMed funds. An investment vehicle, OrbiMed Private Investments VIII, LP, associated with reporting person Peter A. Thompson and OrbiMed Advisors, sold 1,890 shares of Sionna Therapeutics common stock at $44.57 on February 2, 2026.

The same entity sold an additional 29,063 shares at $44.58 on February 3, 2026, leaving 3,530,702 shares of Sionna common stock indirectly beneficially owned after the transactions. The filing notes that the reporting person and related OrbiMed entities disclaim beneficial ownership except to the extent of any pecuniary interest.

Insider Trade Summary

Net Seller: 30,953 shares

Net Sell 2 txns

Insider Thompson Peter A.

Role Director

Sold 30,953 shs ($1.38M)

Type	Security	Shares	Price	Value
Sale	Common Stock	29,063	$44.58	$1.30M
Sale	Common Stock	1,890	$44.57	$84K

Holdings After Transaction: Common Stock — 3,530,702 shares (Indirect, See footnotes)

Footnotes (2)

1. F1. These securities are held of record by OrbiMed Private Investments VIII, LP ("OPI VIII"). OrbiMed Capital GP VIII LLC ("GP VIII") is the general partner of OPI VIII and OrbiMed Advisors LLC ("OrbiMed Advisors") is the managing member of GP VIII. By virtue of such relationships, GP VIII and OrbiMed Advisors may be deemed to have voting and investment power with respect to the shares held by OPI VIII and as a result may be deemed to have beneficial ownership of such shares. OrbiMed Advisors exercises investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho, and W. Carter Neild, each of whom disclaims beneficial ownership of the shares held by OPI VIII. The Reporting Person is a member of OrbiMed Advisors.
2. F2. Each of the Reporting Person, OrbiMed Advisors, and GP VIII disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), except to the extent of its pecuniary interest therein, if any. This report shall not be deemed an admission that any such entity or person is a beneficial owner of such securities for purposes of Section 16 of the Exchange Act, or for any other purpose.

FAQ

What insider-related stock sales were reported for Sionna Therapeutics (SION)?

The filing reports two stock sales by an OrbiMed-affiliated investment vehicle. It sold 1,890 Sionna Therapeutics shares at $44.57 on February 2, 2026, and 29,063 shares at $44.58 on February 3, 2026, as indirectly reported by director Peter A. Thompson.

Who is associated with the Sionna Therapeutics (SION) Form 4 transactions?

The transactions relate to OrbiMed Private Investments VIII, LP, whose interests are managed through OrbiMed Capital GP VIII LLC and OrbiMed Advisors LLC. Director Peter A. Thompson is a member of OrbiMed Advisors and reports the transactions in an indirect capacity with ownership disclaimers.

How many Sionna Therapeutics (SION) shares were sold in total in this Form 4?

The OrbiMed-affiliated entity reported total sales of 30,953 Sionna Therapeutics common shares. It sold 1,890 shares on February 2, 2026, and 29,063 shares on February 3, 2026, at prices of $44.57 and $44.58 per share, respectively, according to the disclosure.

How many Sionna Therapeutics (SION) shares remain held after the reported sales?

After the February 3, 2026 transaction, the OrbiMed-affiliated investment vehicle indirectly held 3,530,702 Sionna Therapeutics common shares. This amount is reported as indirectly beneficially owned, subject to detailed ownership and pecuniary-interest disclaimers described in the footnotes to the filing.

Does Peter A. Thompson directly own the Sionna Therapeutics (SION) shares reported?

The shares are held of record by OrbiMed Private Investments VIII, LP. The filing states that Peter A. Thompson, OrbiMed Advisors, and OrbiMed Capital GP VIII LLC disclaim beneficial ownership of the reported securities, except to the extent of any pecuniary interest they may have.

What do the ownership disclaimers mean in the Sionna Therapeutics (SION) Form 4?

The footnotes explain that OrbiMed entities may be deemed to share voting and investment power over the shares, but each party, including Peter A. Thompson, disclaims beneficial ownership under Exchange Act rules, except for any economic interest, limiting interpretation of the holdings as personal ownership.

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Accepted by SEC EDGAR 02/04/2026 - 07:43 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).

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^*

Thompson Peter A.

(Last) (First) (Middle)

C/O SIONNA THERAPEUTICS, INC.

21 HICKORY DRIVE SUITE 500

(Street)

WALTHAM MA 02451

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Sionna Therapeutics, Inc. [ SION ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

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

3. Date of Earliest Transaction (Month/Day/Year)
02/02/2026

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

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	02/02/2026		S		1,890	D	$44.57	3,559,765	I	See footnotes(1)(2)
Common Stock	02/03/2026		S		29,063	D	$44.58	3,530,702	I	See footnotes(1)(2)

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

Explanation of Responses:

1. These securities are held of record by OrbiMed Private Investments VIII, LP ("OPI VIII"). OrbiMed Capital GP VIII LLC ("GP VIII") is the general partner of OPI VIII and OrbiMed Advisors LLC ("OrbiMed Advisors") is the managing member of GP VIII. By virtue of such relationships, GP VIII and OrbiMed Advisors may be deemed to have voting and investment power with respect to the shares held by OPI VIII and as a result may be deemed to have beneficial ownership of such shares. OrbiMed Advisors exercises investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho, and W. Carter Neild, each of whom disclaims beneficial ownership of the shares held by OPI VIII. The Reporting Person is a member of OrbiMed Advisors.

2. Each of the Reporting Person, OrbiMed Advisors, and GP VIII disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), except to the extent of its pecuniary interest therein, if any. This report shall not be deemed an admission that any such entity or person is a beneficial owner of such securities for purposes of Section 16 of the Exchange Act, or for any other purpose.

	/s/ Peter A. Thompson	02/04/2026
	** 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.
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