SCHEDULE 13D

CUSIP Number(s):

19240Q201

Name of reporting person

Fairmount Funds Management LLC

Check the appropriate box if a member of a Group (See Instructions)

(a)

(b)

SEC use only

Source of funds (See Instructions)

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

Checkbox not checked

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 15,356,918.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 15,356,918.00

Aggregate amount beneficially owned by each reporting person

15,356,918.00

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

Checkbox not checked

Percent of class represented by amount in Row (11)

8.6 %

Type of Reporting Person (See Instructions)

Comment for Type of Reporting Person:

The securities beneficially owned consist of (a) 5,503,418 shares of common stock, $0.001 par value ("Common Stock"), and (b) 9,853,500 shares of Common Stock issuable upon conversion of 39,414 shares of Series A Convertible Preferred Stock, par value $0.001 per share (the "Series A Preferred Stock") directly held by Fairmount Healthcare Fund II L.P. ("Fund II"). Row 13 is based on 179,162,320 shares of Common Stock outstanding as of March 31, 2026, consisting of (i) 162,308,820 shares of Common Stock outstanding as of February 17, 2026, as reported in the Company's most recent Annual Report on Form 10-K, (ii) 7,000,000 shares of Common Stock issued upon the conversion of 28,000 shares of Series A Preferred Stock held by Fund II on March 31, 2026 and (ii) 9,853,500 shares of Common Stock underlying the 39,414 shares of Series A Preferred Stock owned by Fund II.

SCHEDULE 13D

CUSIP Number(s):

19240Q201

Name of reporting person

Fairmount Healthcare Fund II GP LLC

Check the appropriate box if a member of a Group (See Instructions)

(a)

(b)

SEC use only

Source of funds (See Instructions)

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

Checkbox not checked

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 15,356,918.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 15,356,918.00

Aggregate amount beneficially owned by each reporting person

15,356,918.00

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

Checkbox not checked

Percent of class represented by amount in Row (11)

8.6 %

Type of Reporting Person (See Instructions)

Comment for Type of Reporting Person:

The securities beneficially owned consist of (a) 5,503,418 shares of Common Stock, and (b) 9,853,500 shares of Common Stock issuable upon conversion of 39,414 shares of Series A Convertible Preferred Stock directly held by Fund II. Row 13 is based on 179,162,320 shares of Common Stock outstanding as of March 31, 2026, consisting of (i) 162,308,820 shares of Common Stock outstanding as of February 17, 2026, as reported in the Company's most recent Annual Report on Form 10-K, (ii) 7,000,000 shares of Common Stock issued upon the conversion of 28,000 shares of Series A Preferred Stock held by Fund II on March 31, 2026 and (ii) 9,853,500 shares of Common Stock underlying the 39,414 shares of Series A Preferred Stock owned by Fund II.

SCHEDULE 13D

Item 1.

Security and Issuer

(a)

Title of Class of Securities:

Common Stock, $0.001 par value

(b)

Name of Issuer:

Cogent Biosciences, Inc.

(c)

Address of Issuer's Principal Executive Offices:

275 Wyman Street, 3rd Floor, Waltham, MASSACHUSETTS , 02451.

Item 1 Comment:

This Amendment No. 10 amends and supplements the statement on Schedule 13D originally filed with the Securities and Exchange Commission on July 6, 2020, Amendment No. 1 filed on June 21, 2022, Amendment No. 2 filed on June 13, 2023, Amendment No. 3 filed on February 16, 2024, Amendment No. 4 filed on March 27, 2024, Amendment No. 5 filed on April 1, 2024, Amendment No. 6 filed on June 13, 2024, Amendment No. 7 filed on July 14, 2025, Amendment No. 8 filed on November 17, 2025 and Amendment No. 9 filed on January 22, 2026 (as amended, the "Statement" or the "Schedule 13D") by the Reporting Persons with respect to the Common Stock of Cogent Biosciences, Inc. (the "Company"). Unless otherwise defined herein, capitalized terms used in this Amendment No. 10 shall have the meanings ascribed to them in the Statement. Unless amended or supplemented below, the information in the Statement remains unchanged.

Item 3.

Source and Amount of Funds or Other Consideration

Item 3 of the Schedule 13D is hereby amended and supplemented as follows: On March 31, 2026, Fund II delivered to the Company a notice of conversion pursuant to Section 6.4 of the Certificate of Designations of Preferences, Rights and Limitations of Series A Non-Voting Convertible Preferred Stock (the "Certificate of Designations") to convert 28,000 shares of Series A Preferred Stock into 7,000,000 shares of Common Stock, in accordance with the terms of the Certificate of Designations. The conversion was effected for no cash consideration pursuant to the Certificate of Designations.

Item 5.

Interest in Securities of the Issuer

(a)

The information in rows 11 and 13 of each of the cover pages (including the explanatory note in the "Comments") of this Amendment No. 10 is incorporated by reference herein.

(b)

The information in rows 7 through 10 of each of the cover pages of this Amendment No. 10 is incorporated by reference herein. In aggregate, the Reporting Persons have voting and dispositive power over 15,356,918 shares of Common Stock, which is comprised of (a) 5,503,418 shares of Common Stock and (b) 9,853,500 shares of Common Stock currently issuable upon conversion of 39,414 shares of Series A Preferred Stock.

(c)

Item 5(c) of the Schedule 13D is hereby supplemented as follows: On March 31, 2026, Fund II sold in a block trade a total of 7,000,000 shares of Common Stock at a price of $34.66 per share.

Item 7.

Material to be Filed as Exhibits.

99.1 Joint Filing Agreement (incorporated by reference to Exhibit 99.1 to the Schedule 13D filed with the SEC on November 17, 2025)

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Fairmount Funds Management LLC

Signature:	/s/ Peter Harwin
Name/Title:	Peter Harwin, Managing Member
Date:	03/31/2026

Signature:	/s/ Tomas Kiselak
Name/Title:	Tomas Kiselak, Managing Member
Date:	03/31/2026

Fairmount Healthcare Fund II GP LLC

Signature:	/s/ Peter Harwin
Name/Title:	Peter Harwin, Managing Member
Date:	03/31/2026

Signature:	/s/ Tomas Kiselak
Name/Title:	Tomas Kiselak, Managing Member
Date:	03/31/2026