Sionna Therapeutics (SION) insider OrbiMed reports share sales

Rhea-AI Filing Summary

OrbiMed-affiliated funds reported open-market sales of Sionna Therapeutics, Inc. common stock. OrbiMed-related entity OrbiMed Private Investments VIII, LP sold 48,546 shares on May 7, 2026 at $44.61 per share, 59,767 shares on May 8, 2026 at $44.58 per share, and 184,639 shares on May 11, 2026 at $46.22 per share.

All sales were executed as open-market transactions pursuant to a Rule 10b5-1 trading plan. Following these transactions, the OrbiMed-affiliated holder reported owning 2,671,822 shares of Sionna Therapeutics common stock indirectly.

Insider Trade Summary 10b5-1

Net Seller: 292,952 shares ($13,364,065)

Net Sell 3 txns

Insider ORBIMED ADVISORS LLC, OrbiMed Capital GP VIII LLC

Role null | null

Sold 292,952 shs ($13.36M)

Type	Security	Shares	Price	Value
Sale	Common Stock	184,639	$46.22	$8.53M
Sale	Common Stock	59,767	$44.58	$2.66M
Sale	Common Stock	48,546	$44.61	$2.17M

Holdings After Transaction: Common Stock — 2,671,822 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. This report on Form 4 is jointly filed by OrbiMed Advisors and GP VIII. Each of the Reporting Persons 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. The Reporting Persons have designated a representative, Peter A. Thompson, a member of OrbiMed Advisors, to serve on the Issuer's board of directors. 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 May 7, 2026: 48,546 shares at $44.61 Shares sold May 8, 2026: 59,767 shares at $44.58 Shares sold May 11, 2026: 184,639 shares at $46.22 +2 more

5 metrics

Shares sold May 7, 2026 48,546 shares at $44.61 Open-market sale of Sionna Therapeutics common stock

Shares sold May 8, 2026 59,767 shares at $44.58 Open-market sale of Sionna Therapeutics common stock

Shares sold May 11, 2026 184,639 shares at $46.22 Open-market sale of Sionna Therapeutics common stock

Total shares sold 292,952 shares Net shares sold across three transactions

Shares held after transactions 2,671,822 shares Indirect holdings of Sionna Therapeutics common stock

Key Terms

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

5 terms

10b5-1 plan financial

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

A 10b5-1 plan is a pre-arranged strategy that allows company insiders to buy or sell their shares at predetermined times and prices, even while they are aware of confidential information. It acts like a scheduled appointment for trading, helping ensure transactions happen transparently and legally, which can reassure investors that trades are not based on insider knowledge.

beneficial ownership financial

"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

"for purposes of Section 16 of the Exchange Act, or for any other purpose."

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.

Rule 16a-1(a) regulatory

"for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934."

Form 4 Insider Transactions: What Each Field Means →

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^*

ORBIMED ADVISORS LLC

(Last) (First) (Middle)

601 LEXINGTON AVENUE

54TH FLOOR

(Street)

NEW YORK NEW YORK 10022

(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)
05/07/2026

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	05/07/2026		S		48,546(1)	D	$44.61	2,916,228	I	See footnotes((2)(3)
Common Stock	05/08/2026		S		59,767(1)	D	$44.58	2,856,461	I	See footnotes((2)(3)
Common Stock	05/11/2026		S		184,639(1)	D	$46.22	2,671,822	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

1. Name and Address of Reporting Person^*

ORBIMED ADVISORS LLC

(Last) (First) (Middle)

601 LEXINGTON AVENUE

54TH FLOOR

(Street)

NEW YORK NEW YORK 10022

(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^*

OrbiMed Capital GP VIII LLC

(Last) (First) (Middle)

601 LEXINGTON AVENUE

54TH FLOOR

(Street)

NEW YORK NEW YORK 10022-4629

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

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

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.

3. This report on Form 4 is jointly filed by OrbiMed Advisors and GP VIII. Each of the Reporting Persons 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. The Reporting Persons have designated a representative, Peter A. Thompson, a member of OrbiMed Advisors, to serve on the Issuer's board of directors. 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/ Carl L. Gordon, Member of OrbiMed Advisors LLC	05/11/2026
	/s/ Carl L. Gordon, Member of OrbiMed Capital GP VIII LLC	05/11/2026
	** 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)

FAQ

What insider activity did OrbiMed report for Sionna Therapeutics (SION)?

OrbiMed-affiliated entities reported selling Sionna Therapeutics common stock in three open-market transactions. The sales totaled 292,952 shares over several days, with prices in the mid-$40 range, and were conducted under a pre-arranged Rule 10b5-1 trading plan.

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

The insider filings show sales of 48,546, 59,767, and 184,639 Sionna Therapeutics shares. Reported average prices were $44.61, $44.58, and $46.22 per share, respectively, reflecting open-market transactions around the mid-$40s price level on the disclosed trade dates.

How many Sionna Therapeutics (SION) shares does the OrbiMed affiliate hold after the sales?

After completing the reported transactions, the OrbiMed-affiliated holder reported owning 2,671,822 Sionna Therapeutics common shares indirectly. This figure represents the remaining position following the three open-market sales disclosed in the Form 4 insider filing.

Were the Sionna Therapeutics (SION) insider sales made under a Rule 10b5-1 plan?

Yes. A footnote states the securities were sold pursuant to a Rule 10b5-1 trading plan. Such plans are pre-arranged instructions for trading, designed to allow insiders to sell shares over time without making ad hoc timing decisions.

Who is the selling holder in the Sionna Therapeutics (SION) Form 4 filing?

The securities are held of record by OrbiMed Private Investments VIII, LP. OrbiMed Capital GP VIII LLC is its general partner and OrbiMed Advisors LLC is the managing member, which may be deemed to share voting and investment power over the reported Sionna Therapeutics shares.

Do the OrbiMed reporting persons claim full beneficial ownership of Sionna Therapeutics (SION) shares?

The reporting persons disclaim beneficial ownership of the reported Sionna Therapeutics securities except to the extent of any pecuniary interest. They state the Form 4 should not be considered an admission of beneficial ownership for Section 16 or other purposes.