Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 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 that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person * RA CAPITAL MANAGEMENT, L.P. 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 __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 200 BERKELEY STREET, 18TH FLOOR, 3. Date of Earliest Transaction (Month/Day/Year) 10/24/2025 (Street) BOSTON, MA 02116 4. If Amendment, Date Original Filed (Month/Day/Year) 6. Individual or Joint/Group Filing (Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) 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 10/24/2025 S 14,116 D $39.5 6,909,249 I See footnotes(1)(2) Common Stock 10/24/2025 S 122,271 D $39.5 747,380 I See footnotes(2)(3) Common Stock 10/24/2025 S 66,672 D $39.5 2,257,826 I See footnotes(2)(4) Common Stock 10/24/2025 S 107,941 D $39.5 219,867 I See footnotes(2)(5) Common Stock 10/28/2025 S 3,624 D $39.58(6) 6,905,625 I See footnotes(1)(2) Common Stock 10/28/2025 S 31,392 D $39.58(6) 715,988 I See footnotes(2)(3) Common Stock 10/28/2025 S 17,118 D $39.58(6) 2,240,708 I See footnotes(2)(4) Common Stock 10/28/2025 S 10,476 D $39.58(6) 209,391 I See footnotes(2)(5)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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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 Underlying Securities (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 of Derivative Security: 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

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X	X
RA Capital Healthcare Fund LP C/O RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X	X
RA Capital Nexus Fund, L.P. C/O RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X
RA Capital Nexus Fund III, L.P. C/O RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X
Kolchinsky Peter C/O RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X	X
Shah Rajeev M. C/O RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA 02116	X	X

Signatures

/s/ Peter Kolchinsky, Manager of RA Capital Management, L.P.		10/28/2025
**Signature of Reporting Person		Date
/s/ Peter Kolchinsky, Manager of RA Capital Healthcare Fund GP, LLC, the General Partner of RA Capital Healthcare Fund, L.P.		10/28/2025
**Signature of Reporting Person		Date
/s/ Peter Kolchinsky, Manager of RA Capital Nexus Fund GP, LLC, the General Partner of RA Capital Nexus Fund, L.P.		10/28/2025
**Signature of Reporting Person		Date
/s/ Peter Kolchinsky, Manager of RA Capital Nexus Fund III GP, LLC, the General Partner of RA Capital Nexus Fund III, L.P.		10/28/2025
**Signature of Reporting Person		Date
/s/ Peter Kolchinsky, individually		10/28/2025
**Signature of Reporting Person		Date
/s/ Rajeev Shah, individually		10/28/2025
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	Held directly by RA Capital Healthcare Fund, L.P. (the "Fund").
(2)	RA Capital Management, L.P. (the "Adviser") is the investment manager for the Fund, RA Capital Nexus Fund, L.P. (the "Nexus Fund"), RA Capital Nexus III Fund, L.P. (the "Nexus Fund III"), and a separately managed account (the "Account"). 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. The Adviser, the Adviser GP, the Fund, the Nexus Fund, the Nexus Fund III, Dr. Kolchinsky and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.
(3)	Held directly by the Nexus Fund.
(4)	Held directly by Nexus Fund III.
(5)	Held directly by the Account.
(6)	The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $39.50 to $39.81 inclusive. The Reporting Persons undertake 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 range set forth in this footnote.
Remarks: Joshua Resnick, a Partner of the Adviser, serves on the Issuer's board of directors.

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