Fairmount Funds trims Cogent Biosciences (COGT) position after 7M-share block sale

Rhea-AI Filing Summary

Fairmount Funds Management LLC and affiliates report updated ownership in Cogent Biosciences after converting preferred stock and selling shares. They beneficially own 15,356,918 shares of common stock, representing 8.6% of the company. This includes 5,503,418 common shares and 9,853,500 shares currently issuable upon conversion of 39,414 shares of Series A Convertible Preferred Stock.

On March 31, 2026, Fairmount Healthcare Fund II L.P. converted 28,000 shares of Series A Preferred Stock into 7,000,000 common shares for no cash consideration under the Certificate of Designations, then sold 7,000,000 common shares in a block trade at $34.66 per share. The ownership percentage is based on 179,162,320 common shares outstanding as of March 31, 2026.

Insights

Equity ownership and block-trade analyst

Large holder updates Cogent stake after preferred conversion and 7M-share block sale.

Fairmount-related entities now report beneficial ownership of 15,356,918 Cogent Biosciences common shares, equal to 8.6% of the company. The position combines 5,503,418 existing common shares with 9,853,500 shares issuable from 39,414 shares of Series A Convertible Preferred Stock.

On March 31, 2026, Fairmount Healthcare Fund II L.P. converted 28,000 Series A Preferred shares into 7,000,000 common shares for no cash consideration under the Certificate of Designations, then executed a 7,000,000-share block trade at $34.66 per share. Despite this sizable sale, the group remains a significant shareholder with shared voting and dispositive power over the reported shares.

Key Figures

Beneficial ownership: 15,356,918 shares Ownership percentage: 8.6% Common shares held: 5,503,418 shares +5 more

8 metrics

Beneficial ownership 15,356,918 shares Common stock beneficially owned by reporting persons

Ownership percentage 8.6% Percent of Cogent common stock class represented

Common shares held 5,503,418 shares Outstanding Cogent common stock held by Fund II

Shares issuable on conversion 9,853,500 shares Common stock issuable from 39,414 Series A Preferred shares

Block trade size 7,000,000 shares Common shares sold on March 31, 2026

Block trade price $34.66 per share Sale price for 7,000,000-share block trade

Shares outstanding 179,162,320 shares Cogent common stock outstanding as of March 31, 2026

Converted preferred shares 28,000 shares Series A Preferred converted into 7,000,000 common shares

Key Terms

beneficially owned, Series A Convertible Preferred Stock, Certificate of Designations, block trade, +1 more

5 terms

beneficially owned financial

"The securities beneficially owned consist of (a) 5,503,418 shares of common stock"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

Series A Convertible Preferred Stock financial

"9,853,500 shares of Common Stock issuable upon conversion of 39,414 shares of Series A Convertible Preferred Stock"

Series A convertible preferred stock is a class of shares sold in an early funding round that gives investors a mix of protection and upside: it pays a priority claim over common shares if the company is sold or closes, but can be converted into ordinary shares to share in future growth. Think of it like a hybrid between a safer stake and a ticket to ownership; it matters to investors because it affects who controls the company, how future gains are split, and how much their investment is protected from downside.

Certificate of Designations regulatory

"pursuant to Section 6.4 of the Certificate of Designations of Preferences, Rights and Limitations"

block trade financial

"On March 31, 2026, Fund II sold in a block trade a total of 7,000,000 shares"

A block trade is a large, privately arranged sale or purchase of a company's shares or bonds between big investors, often negotiated to avoid upsetting the public market price. Think of it like selling a truckload of goods directly to one buyer instead of unloading it on a busy street — it moves a lot of supply at once and can signal shifting demand, affect immediate liquidity, and influence short-term stock prices.

Schedule 13D regulatory

"This Amendment No. 10 amends and supplements the statement on originally filed"

A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 10)

Cogent Biosciences, Inc.

(Name of Issuer)

Common Stock, $0.001 par value

(Title of Class of Securities)

19240Q201

(CUSIP Number)

Ms. Erin O'Connor
Fairmount Funds Management LLC, 200 Barr Harbor Drive, Suite 400
West Conshohocken, PA, 19428
(267) 262-5300

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

03/31/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): 19240Q201

1

Name of reporting person

Fairmount Funds Management LLC

2

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

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

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

6

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

11

Aggregate amount beneficially owned by each reporting person

15,356,918.00

12

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

13

Percent of class represented by amount in Row (11)

8.6 %

14

Type of Reporting Person (See Instructions)

IA

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

1

Name of reporting person

Fairmount Healthcare Fund II GP LLC

2

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

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

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

6

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

11

Aggregate amount beneficially owned by each reporting person

15,356,918.00

12

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

13

Percent of class represented by amount in Row (11)

8.6 %

14

Type of Reporting Person (See Instructions)

OO

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

FAQ

How many Cogent Biosciences (COGT) shares do Fairmount entities currently beneficially own?

Fairmount-related entities beneficially own 15,356,918 shares of Cogent Biosciences common stock. This total includes 5,503,418 outstanding common shares plus 9,853,500 shares currently issuable upon conversion of 39,414 shares of Series A Convertible Preferred Stock held by Fairmount Healthcare Fund II L.P.

What percentage of Cogent Biosciences (COGT) does Fairmount now hold according to this Schedule 13D amendment?

The reporting persons state they beneficially own 8.6% of Cogent Biosciences’ common stock. This percentage is calculated using 179,162,320 shares outstanding as of March 31, 2026, including existing shares, recent preferred conversions, and shares underlying remaining Series A Preferred Stock.

What transaction did Fairmount Healthcare Fund II L.P. execute on March 31, 2026 involving Cogent Biosciences (COGT)?

On March 31, 2026, Fairmount Healthcare Fund II L.P. sold 7,000,000 Cogent Biosciences common shares in a block trade. The shares were sold at a price of $34.66 per share, following the conversion of 28,000 shares of Series A Preferred Stock into 7,000,000 common shares that same day.

How were Cogent Biosciences (COGT) preferred shares converted in this filing?

On March 31, 2026, 28,000 shares of Cogent’s Series A Non-Voting Convertible Preferred Stock were converted into 7,000,000 common shares. The conversion followed Section 6.4 of the Certificate of Designations and was effected for no cash consideration under the stated terms.

What Cogent Biosciences (COGT) capital structure figure did Fairmount use to compute its 8.6% ownership?

The filing bases the 8.6% ownership on 179,162,320 Cogent Biosciences common shares outstanding as of March 31, 2026. This total reflects 162,308,820 common shares reported as of February 17, 2026 plus additional shares from preferred stock conversions and remaining convertible preferred holdings.

What components make up Fairmount’s Cogent Biosciences (COGT) beneficial ownership position?

Fairmount’s position consists of 5,503,418 Cogent common shares and 9,853,500 common shares issuable upon conversion of 39,414 Series A Convertible Preferred shares. All are attributed to Fairmount Healthcare Fund II L.P., over which the reporting entities share voting and dispositive power under this amendment.