# EDGAR Filing Document

**Accession Number:** 0001622229
**File Stem:** 0001104659-26-038056
**Filing Date:** 2026-3
**Character Count:** 10819
**Document Hash:** a67611ebbf279d0f2da302e3f3b4192f
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-26-038056.hdr.sgml**: 20260331

**ACCESSION NUMBER**: 0001104659-26-038056

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13D/A

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20260331

**DATE AS OF CHANGE**: 20260331

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Cogent Biosciences, Inc.
- **CENTRAL INDEX KEY:** 0001622229
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 465308248
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-90431
- **FILM NUMBER:** 26824373

**BUSINESS ADDRESS:**
- **STREET 1:** 275 WYMAN STREET
- **STREET 2:** 3RD FLOOR
- **CITY:** WALTHAM
- **STATE:** MA
- **ZIP:** 02451
- **BUSINESS PHONE:** 617-945-5576

**MAIL ADDRESS:**
- **STREET 1:** 275 WYMAN STREET
- **STREET 2:** 3RD FLOOR
- **CITY:** WALTHAM
- **STATE:** MA
- **ZIP:** 02451

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Unum Therapeutics Inc.
- **DATE OF NAME CHANGE:** 20180402

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Unum Therapeutics, Inc.
- **DATE OF NAME CHANGE:** 20141014
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Fairmount Funds Management LLC
- **CENTRAL INDEX KEY:** 0001802528

**ORGANIZATION NAME:**
- **EIN:** 364841215
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A

**BUSINESS ADDRESS:**
- **STREET 1:** 200 BARR HARBOR DRIVE
- **STREET 2:** SUITE 400
- **CITY:** WEST CONSHOHOCKEN
- **STATE:** PA
- **ZIP:** 19428
- **BUSINESS PHONE:** 267-262-5300

**MAIL ADDRESS:**
- **STREET 1:** 200 BARR HARBOR DRIVE
- **STREET 2:** SUITE 400
- **CITY:** WEST CONSHOHOCKEN
- **STATE:** PA
- **ZIP:** 19428

### UNITED STATES 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)*

**—**

*(CUSIP Number)*

**Ms. Erin O'Connor**<br>Fairmount Funds Management LLC<br>200 Barr Harbor Drive, Suite 400<br>West Conshohocken PA 19428<br>(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)*

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Fairmount Funds Management LLC** | Name of reporting person<br>**Fairmount Funds Management LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**15356918.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**15356918.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**15356918.00** | Aggregate amount beneficially owned by each reporting person<br>**15356918.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**8.6%** | Percent of class represented by amount in Row (11)<br>**8.6%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IA** | Type of Reporting Person (See Instructions)<br>**IA** | |

---

**Comment for 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.

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Fairmount Healthcare Fund II GP LLC** | Name of reporting person<br>**Fairmount Healthcare Fund II GP LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**15356918.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**15356918.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**15356918.00** | Aggregate amount beneficially owned by each reporting person<br>**15356918.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**8.6%** | Percent of class represented by amount in Row (11)<br>**8.6%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

**Comment for 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.

**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, MA, 02451

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 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.

### 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.

**Reporting Person:** Fairmount Funds Management LLC

**Signature:** /s/ Peter Harwin

**Name/Title:** Peter Harwin, Managing Member

**Date:** 03/31/2026

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.

**Reporting Person:** Fairmount Healthcare Fund II GP LLC

**Signature:** /s/ Peter Harwin

**Name/Title:** Peter Harwin, Managing Member

**Date:** 03/31/2026