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

OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response... 0.5

(Print or Type Responses)

1. Name and Address of Reporting Person * Fairmount Funds Management LLC 2. Issuer Name and Ticker or Trading Symbol Korsana Biosciences, Inc. [KRSA] 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 BARR HARBOR DRIVE, SUITE 400 3. Date of Earliest Transaction (Month/Day/Year) 09/09/2026 (Street) WEST CONSHOHOCKEN, PA 19428 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

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
	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 control number.		SEC 1474 (9-02)

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

Stock Option (Right to Buy)

$26.2

09/09/2026

A

48,445

(1)

09/09/2036

Common Stock

48,445

$ 0

48,445

I(2)

By: Tomas Kiselak

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Fairmount Funds Management LLC 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN, PA 19428	X	X
Fairmount Healthcare Fund II L.P. 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN, PA 19428	X	X
Fairmount Healthcare Co-Invest VI L.P. 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN, PA 19428	X	X
Kiselak Tomas 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN, PA 19428	X	X
Harwin Peter Evan 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN, PA 19428	X	X

Signatures

/s/ Peter Harwin, Managing Member of Fairmount Funds Management LLC		09/10/2026
**Signature of Reporting Person		Date
/s/ Peter Harwin, Managing Member of Fairmount Healthcare Fund II L.P.		09/10/2026
**Signature of Reporting Person		Date
/s/ Peter Harwin, Managing Member of Fairmount Healthcare Co-Invest VI L.P.		09/10/2026
**Signature of Reporting Person		Date
/s/ Tomas Kiselak		09/10/2026
**Signature of Reporting Person		Date
/s/ Peter Harwin		09/10/2026
**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)	This option represents a right to purchase 48,445 shares of the Issuer's common stock. This option will vest in equal monthly installments through September 9, 2029, subject to the Reporting Person's continued service to the Issuer on each such vesting date.
(2)	Fairmount Funds Management LLC ("Fairmount") is the investment manager for Fairmount Healthcare Fund II L.P. ("Fund II") and Fairmount Healthcare Co-Invest VI L.P. ("Co-Invest"). Peter Harwin and Tomas Kiselak are the managers of Fairmount. Under Mr. Kiselak's arrangement with Fairmount, Mr. Kiselak holds the option for one or more investment vehicles managed by Fairmount (each, a "Fairmount Fund"). Mr. Kiselak is obligated to turn over to Fairmount any net cash or stock received from the option for the benefit of such Fairmount Fund. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.
Remarks: Fairmount, Fund II and Co-Invest may each be deemed a director by deputization of the Issuer by virtue of the fact that Tomas Kiselak serves on the board of directors of the Issuer and is a manager of Fairmount.

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure. Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB number.