OrbiMed fund tied to Sionna (SION) director sells 85,918 shares

Rhea-AI Filing Summary

Sionna Therapeutics director-affiliated fund reports share sale. An entity associated with director Peter A. Thompson, OrbiMed Private Investments VIII, LP, sold 85,918 shares of Sionna Therapeutics common stock in an open-market transaction at $44.86 per share pursuant to a Rule 10b5-1 plan. Following the sale, the entity continues to hold 2,469,959 shares indirectly. OrbiMed-related entities and the reporting person may be deemed to have beneficial ownership through control relationships but each disclaims beneficial ownership beyond any pecuniary interest.

Insider Trade Summary 10b5-1

Net Seller: 85,918 shares ($3,854,281)

Net Sell 1 txn

Insider Thompson Peter A.

Role null

Sold 85,918 shs ($3.85M)

Type	Security	Shares	Price	Value
Sale	Common Stock	85,918	$44.86	$3.85M

Holdings After Transaction: Common Stock — 2,469,959 shares (Indirect, See footnotes)

Footnotes (1)

1. These securities were sold pursuant to a 10b5-1 plan. 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. 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.

Key Figures

Shares sold: 85,918 shares Sale price per share: $44.86/share Shares held after sale: 2,469,959 shares +2 more

5 metrics

Shares sold 85,918 shares Open-market sale on 2026-07-07

Sale price per share $44.86/share Open-market transaction

Shares held after sale 2,469,959 shares Indirect holdings following transaction

Net shares sold 85,918 shares Net sell direction in this filing

Sell transactions 1 transaction Non-derivative open-market sale

Key Terms

Rule 10b5-1 plan, beneficial ownership, pecuniary interest, Section 16, +1 more

5 terms

Rule 10b5-1 plan regulatory

"These securities were sold pursuant to a 10b5-1 plan."

A Rule 10b5-1 plan is a prearranged, written schedule that lets corporate insiders buy or sell company stock at set times or amounts, even if they later learn material nonpublic information. Think of it like setting an automatic thermostat for trades: it creates a clear record that trades were planned in advance, reducing the risk of insider-trading accusations and helping investors trust that insider transactions are routine rather than based on secret information.

beneficial ownership regulatory

"may be deemed to have beneficial ownership of such shares."

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 pecuniary interest therein, if any."

Section 16 regulatory

"beneficial owner of such securities for purposes of Section 16 of the Exchange Act"

Section 16 is a U.S. securities law rule that governs the trading and disclosure obligations of company insiders — typically officers, directors and large shareholders — to promote transparency and deter unfair profit-taking. It requires insiders to publicly report their stock trades and allows companies or the issuer to reclaim quick, short-term profits from certain insider trades, like a scoreboard and a refund policy that help investors see and limit possible insider advantage.

voting and investment power financial

"may be deemed to have voting and investment power with respect to the shares"

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Form 4 Insider Transactions: What Each Field Means →

Available on EDGAR 07/09/2026 - 04:48 PM Accepted by SEC EDGAR 07/09/2026 - 04:47 PM Learn about SEC filing dates

FAQ

What did the Sionna Therapeutics (SION) Form 4 filing report?

The Form 4 reports an open-market sale of 85,918 Sionna Therapeutics common shares at $44.86 each by OrbiMed Private Investments VIII, LP, an entity associated with director Peter A. Thompson, under a pre-established Rule 10b5-1 trading plan.

Who actually sold Sionna Therapeutics (SION) shares in this Form 4?

The sale was made by OrbiMed Private Investments VIII, LP, not directly by Peter A. Thompson. OrbiMed Capital GP VIII LLC and OrbiMed Advisors LLC are affiliated entities that may be deemed to have voting and investment power over the shares held by this fund.

How many Sionna Therapeutics (SION) shares were sold and at what price?

The filing shows 85,918 shares of Sionna Therapeutics common stock were sold in an open-market transaction at a price of $44.86 per share. This transaction was executed pursuant to a Rule 10b5-1 trading plan established in advance.

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

After the transaction, OrbiMed Private Investments VIII, LP is reported as holding 2,469,959 Sionna Therapeutics common shares indirectly. This post-transaction balance reflects the remaining position attributed to the fund in the Form 4 filing.

Was the Sionna Therapeutics (SION) share sale part of a pre-planned program?

Yes. The footnotes state that the securities were sold pursuant to a Rule 10b5-1 plan. Such plans are pre-arranged trading programs that allow insiders or related entities to sell shares according to predetermined instructions, reducing the role of short-term discretion.

Does Peter A. Thompson claim full beneficial ownership of the Sionna (SION) shares?

No. The filing states that Peter A. Thompson, OrbiMed Advisors, and OrbiMed Capital GP VIII LLC each disclaim beneficial ownership of the reported securities, except to the extent of any pecuniary interest. The report is not an admission of beneficial ownership under Section 16.

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 MASSACHUSETTS 02451

(City) (State) (Zip)

UNITED STATES

(Country)

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)

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
07/07/2026

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

X	Form filed by One Reporting Person
	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	07/07/2026		S		85,918(1)	D	$44.86	2,469,959	I	See footnotes(2)(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

Explanation of Responses:

1. These securities were sold pursuant to a 10b5-1 plan.

2. 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.

3. 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	07/09/2026
	** 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)