CCCC insider reports RSU vesting and 5,644-share tax withholding

Rhea-AI Filing Summary

C4 Therapeutics (CCCC) reported an insider equity change by its Chief Scientific Officer. On 10/28/2025, 19,200 shares of Common Stock were acquired at $0.00 upon vesting of previously disclosed RSUs. To cover taxes, the issuer withheld 5,644 shares at $2.58, which the filing states does not represent a sale by the reporting person. Following these transactions, the officer directly beneficially owned 99,356 shares.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

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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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 for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Mahaney Paige

(Last) (First) (Middle)

C4 THERAPEUTICS, INC.

490 ARSENAL WAY, SUITE 120

(Street)

WATERTOWN MA 02472

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
C4 Therapeutics, Inc. [ CCCC ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Scientific Officer

3. Date of Earliest Transaction (Month/Day/Year)
10/28/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

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	10/28/2025		M(1)	V	19,200	A	$0.00	105,000	D
Common Stock	10/28/2025		F(2)		5,644	D	$2.58	99,356	D

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 Securities Underlying Derivative Security (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: 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

Explanation of Responses:

1. Reflects the acquisition of shares of Common Stock upon vesting of a previously disclosed grant of restricted stock units ("RSUs"). The grant of RSUs was initially reported in Table I of the Form 4 filed by the Reporting Person on October 28, 2024.

2. Represents shares withheld by the Issuer to satisfy tax withholding obligations in connection with the vesting and settlement of RSUs and does not represent a sale by the Reporting Person.

	/s/ Shagha Russell, Attorney-in-Fact	10/30/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* 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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
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FAQ

What did CCCC disclose in this Form 4?

RSU vesting of 19,200 shares and tax withholding of 5,644 shares on 10/28/2025.

How many RSUs vested for the CCCC officer?

19,200 shares of Common Stock vested at $0.00 per share.

How many shares were withheld for taxes and at what price?

The issuer withheld 5,644 shares at $2.58 to satisfy tax obligations.

What is the officer’s beneficial ownership after these transactions?

Direct beneficial ownership is 99,356 shares after the reported transactions.

Does the tax withholding count as a sale by the officer?

No. The filing states the withholding does not represent a sale by the reporting person.

What is the reporting person’s role at CCCC?

The reporting person is the Chief Scientific Officer.

When did the transactions occur?

The transactions took place on 10/28/2025.