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cccc-202602260001662579false00016625792026-02-262026-02-26

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 26, 2026

C4 THERAPEUTICS, INC.

(Exact name of Registrant as Specified in Its Charter)

Delaware 001-39567 47-5617627

(State or Other Jurisdiction of Incorporation) (Commission File Number) (IRS Employer Identification No.)

490 Arsenal Way,   Suite 120 Watertown,  MA 02472

(Address of Principal Executive Offices) (Zip Code)

Registrant’s Telephone Number, Including Area Code: (617) 231-0700 Not Applicable (Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

o Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class Trading Symbol(s) Name of each exchange on which registered

Common Stock, $0.0001 par value per share

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The Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company o If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

Item 2.02 Results of Operations and Financial Condition. On February 26, 2026, C4 Therapeutics, Inc. (the “Company”) issued a press release announcing its financial results and business highlights for the quarter and fiscal year ended December 31, 2025. A copy of the press release is being furnished as Exhibit 99.1 to this Current Report on Form 8-K. The information contained in Item 2.02 of this Current Report on Form 8-K and Exhibit 99.1 attached hereto is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Item 9.01 Financial Statements and Exhibits. (d) Exhibits. The exhibits shall be deemed to be filed or furnished, depending on the relevant item requiring such exhibit, in accordance with the provisions of Item 601 of Regulation S-K (17 CFR 229.601) and Instruction B.2 to this form.

Exhibit Number Description

99.1 Press release issued February 26, 2026

104 Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

C4 Therapeutics, Inc.

Date: February 26, 2026 By: /s/ Kendra R. Adams

Kendra R. Adams

Chief Financial Officer and Treasurer

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 6, 2025

C4 THERAPEUTICS, INC.

(Exact name of Registrant as Specified in Its Charter)

Delaware001-3956747-5617627 (State or Other Jurisdiction of Incorporation) (Commission File Number)(IRS Employer Identification No.)

490 Arsenal Way,   Suite 120 Watertown,  MA 02472 (Address of Principal Executive Offices)(Zip Code)

Registrant’s Telephone Number, Including Area Code: (617) 231-0700 Not Applicable (Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

oWritten communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) oSoliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) oPre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) oPre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each classTrading Symbol(s) Name of each exchange on which registered Common Stock, $0.0001 par value per shareCCCCThe Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company o If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

Item 2.02 Results of Operations and Financial Condition. On November 6, 2025, C4 Therapeutics, Inc. (the “Company”) issued a press release announcing its financial results and business highlights for the quarter ended September 30, 2025. A copy of the press release is being furnished as Exhibit 99.1 to this Current Report on Form 8-K. The information contained in Item 2.02 of this Current Report on Form 8-K and Exhibit 99.1 attached hereto is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended (the “Securities Act”), or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Item 9.01 Financial Statements and Exhibits. (d) Exhibits. The exhibits shall be deemed to be filed or furnished, depending on the relevant item requiring such exhibit, in accordance with the provisions of Item 601 of Regulation S-K (17 CFR 229.601) and Instruction B.2 to this form.

Exhibit Number Description 99.1Press release issued November 6, 2025

104Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

C4 Therapeutics, Inc.

Date: November 6, 2025 By:/s/ Jolie M. Siegel Jolie M. Siegel Chief Legal Officer and Secretary

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 7, 2025

C4 THERAPEUTICS, INC.

(Exact name of Registrant as Specified in Its Charter)

Delaware001-3956747-5617627 (State or Other Jurisdiction of Incorporation) (Commission File Number)(IRS Employer Identification No.)

490 Arsenal Way,   Suite 120 Watertown,  MA 02472 (Address of Principal Executive Offices)(Zip Code)

Registrant’s Telephone Number, Including Area Code: (617) 231-0700 Not Applicable (Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

oWritten communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) oSoliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) oPre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) oPre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each classTrading Symbol(s) Name of each exchange on which registered Common Stock, $0.0001 par value per shareCCCCThe Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company o If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

Item 2.02 Results of Operations and Financial Condition. On August 7, 2025, C4 Therapeutics, Inc. (the “Company”) issued a press release announcing its financial results and business highlights for the quarter ended June 30, 2025. A copy of the press release is being furnished as Exhibit 99.1 to this Current Report on Form 8-K. The information contained in Item 2.02 of this Current Report on Form 8-K and Exhibit 99.1 attached hereto is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended (the “Securities Act”), or the Exchange Act, except as expressly set forth by specific reference in such a filing.

Item 7.01 Regulation FD Disclosure. On August 7, 2025, the Company posted a corporate presentation on its website at https://ir.c4therapeutics.com/events-presentations. A copy of the presentation is furnished herewith as Exhibit 99.2 to this Current Report on Form 8-K. The information contained in Item 7.01 of this Current Report on Form 8-K and Exhibit 99.2 attached hereto is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Exchange Act, or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act or the Exchange Act, except as expressly set forth by specific reference in such a filing. The furnishing of this information hereby shall not be deemed an admission as to the materiality of any such information.

Item 8.01 Other Events. On August 7, 2025, the Company provided the following updates from its Phase 1 clinical trial of cemsidomide: •Completed enrollment and dose escalation for the Phase 1 trial of cemsidomide in multiple myeloma (“MM”) and non-Hodgkin’s Lymphoma (“NHL”). As of the data cutoff date of July 23, 2025, cemsidomide continued to demonstrate a well-tolerated profile and compelling response rates in MM and NHL, with an overall response rate in the MM cemsidomide plus dexamethasone arm of 40% at the 75 μg and 50% at the 100 μg dose levels. The highest dose level studied in both indications was 100 μg once daily. •By year-end 2025, Company expects to align with the FDA on a recommended Phase 2 dose based on the existing Phase 1 MM data, and remains on track to initiate registrational development of cemsidomide in early 2026. The next phase of development will evaluate cemsidomid