C4 Therapeutics reports that Sirenia Capital Management and Alex Silverstein collectively beneficially own 23,505,000 shares of Common Stock, representing 9.9% of the class after applying a 9.99% ownership blocker.
The filing states the percentage is calculated using 97,578,175 shares outstanding as of February 23, 2026 and notes that the reported holdings include 14,170,000 shares issuable upon exercise of warrants subject to the 9.99% Blocker; as a result, the Reporting Persons cannot currently exercise all warrants because of that limitation.
Positive
None.
Negative
None.
Insights
Sirenia and its managing member report a near-10% economic position in C4 Therapeutics, limited by a 9.99% exercise blocker.
The filing lists 23,505,000 shares beneficially associated with Sirenia/Silverstein, calculated on an outstanding share base of February 23, 2026 (97,578,175 shares). It explicitly includes 14,170,000 shares issuable on warrant exercise but notes the 9.99% Blocker prevents full exercise.
Cash-flow treatment and planned dispositions are not disclosed in the excerpt; subsequent filings would show any changes in exercised warrants or transfers that affect percentage ownership.
The Schedule 13G reflects passive reporting mechanics and a contractual ownership limit tied to the Reported Warrants.
The statement is filed under joint filing procedures and includes a Joint Filing Agreement as Exhibit 99.1. The language clarifies calculation methodology and the operative qualifier: the 9.99% Blocker governs exercise capacity.
Regulatory implications are routine for a >5% holding disclosure; filings that would follow an exercise, sale, or amendment would disclose changes in voting/dispositive power.
Key Figures
Beneficially owned shares:23,505,000 sharesPercent of class:9.9%Shares outstanding used for calculation:97,578,175 shares+2 more
5 metrics
Beneficially owned shares23,505,000 sharesReported on cover page as beneficial ownership
Percent of class9.9%Calculated after applying the 9.99% Blocker
Shares outstanding used for calculation97,578,175 sharesOutstanding as of <date>February 23, 2026</date> per issuer 2025 Form 10‑K
Warrants issuable14,170,000 sharesShares issuable upon exercise of the Reported Warrants
CUSIP12529R107CUSIP for C4 Therapeutics Common Stock
Key Terms
9.99% Blocker, Reported Warrants, Schedule 13G
3 terms
9.99% Blockerregulatory
"The Reported Warrants are subject to the 9.99% Blocker"
Reported Warrantsfinancial
"Includes 14,170,000 shares ... issuable upon exercise of the Reported Warrants"
Schedule 13Gregulatory
"This statement is filed by: Sirenia Capital Management LP ... (Schedule 13G context)"
A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
C4 Therapeutics, Inc.
(Name of Issuer)
Common Stock, par value $0.0001 per share
(Title of Class of Securities)
12529R107
(CUSIP Number)
03/31/2026
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
Rule 13d-1(b)
Rule 13d-1(c)
Rule 13d-1(d)
schemaVersion:
SCHEDULE 13G
CUSIP Number(s):
12529R107
1
Names of Reporting Persons
Sirenia Capital Management LP
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
23,505,000.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
23,505,000.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
23,505,000.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
9.9 %
12
Type of Reporting Person (See Instructions)
IA, PN
Comment for Type of Reporting Person: Includes 14,170,000 shares of Common Stock (as defined in Item 2(a)) issuable upon exercise of the Reported Warrants (as defined in Item 4(a)). As more fully described in Item 4, the Reported Warrants are subject to the 9.99% Blocker (as defined in Item 4(a)) and the percentage set forth on row (11) gives effect to the 9.99% Blocker. However, rows (6), (8) and (9) show the number of shares of Common Stock that would be issuable upon the full exercise of the Reported Warrants and does not give effect to the 9.99% Blocker. Therefore, the actual number of shares of Common Stock beneficially owned by such Reporting Person, after giving effect to the 9.99% Blocker, is less than the number of securities reported on rows (6), (8) and (9).
SCHEDULE 13G
CUSIP Number(s):
12529R107
1
Names of Reporting Persons
Alex Silverstein
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
23,505,000.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
23,505,000.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
23,505,000.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
9.9 %
12
Type of Reporting Person (See Instructions)
HC, IN
Comment for Type of Reporting Person: Includes 14,170,000 shares of Common Stock issuable upon exercise of the Reported Warrants. As more fully described in Item 4, the Reported Warrants are subject to the 9.99% Blocker and the percentage set forth on row (11) gives effect to the 9.99% Blocker. However, rows (6), (8) and (9) show the number of shares of Common Stock that would be issuable upon the full exercise of the Reported Warrants and does not give effect to the 9.99% Blocker. Therefore, the actual number of shares of Common Stock beneficially owned by such Reporting Person, after giving effect to the 9.99% Blocker, is less than the number of securities reported on rows (6), (8) and (9).
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
C4 Therapeutics, Inc.
(b)
Address of issuer's principal executive offices:
490 Arsenal Way, Suite 120, Watertown, MA 02472
Item 2.
(a)
Name of person filing:
This statement is filed by:
(i) Sirenia Capital Management LP ("Sirenia") with respect to the common stock, par value $0.0001 per share ("Common Stock"), of C4 Therapeutics, Inc. (the "Issuer") held by, and issuable upon exercise of the Reported Warrants held by, SILV Fund, Ltd. (the "Sirenia Fund"), an investment fund it manages; and
(ii) Alex Silverstein ("Mr. Silverstein"), the managing member of Sirenia Capital Management GP LLC, the general partner of Sirenia, with respect to the Common Stock held by, and issuable upon exercise of Reported Warrants held by, the Sirenia Fund.
The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons."
The filing of this statement should not be construed as an admission that any of the foregoing persons or any Reporting Person is, for the purposes of Section 13 of the Securities Exchange Act of 1934, the beneficial owner of the securities reported herein.
Sirenia and Mr. Silverstein have entered into a Joint Filing Agreement, a copy of which is filed with this Schedule 13G as Exhibit 99.1, pursuant to which they have agreed to file this Schedule 13G jointly in accordance with the provisions of Rule 13d-1(k) of the Securities Exchange Act of 1934 (the "Act").
(b)
Address or principal business office or, if none, residence:
The address of the principal business office of Sirenia and Mr. Silverstein is 1674 Meridian Avenue, Suite 320, Miami Beach, FL 33139.
(c)
Citizenship:
Sirenia is a Delaware limited partnership. Mr. Silverstein is a United States citizen.
(d)
Title of class of securities:
Common Stock, par value $0.0001 per share
(e)
CUSIP Number(s):
12529R107
Item 3.
If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)
An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)
An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)
A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)
A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)
A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
(k)
Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.
Ownership
(a)
Amount beneficially owned:
The information required by Item 4(a) is set forth in Row 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
The percentage set forth in this Schedule 13G is calculated based upon an aggregate of 97,578,175 shares of Common Stock outstanding as of February 23, 2026, as reported in the Issuer's Annual Report on Form 10-K for the fiscal year ended December 31, 2025, filed with the Securities and Exchange Commission on February 26, 2026, and assumes the exercise of the warrants (the "Reported Warrants") held by the Sirenia Fund.
Pursuant to the terms of the Reported Warrants, the Reporting Persons cannot exercise any of the Reported Warrants to the extent the Reporting Persons would beneficially own, after any such exercise, more than 9.99% of the outstanding shares of Common Stock (the "9.99% Blocker") and the percentage set forth in Row (11) of the cover page for each of the Reporting Persons gives effect to the 9.99% Blocker. Consequently, at this time, the Reporting Persons are not able to exercise all of such Reported Warrants due to the 9.99% Blocker.
(b)
Percent of class:
9.9%
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
The information required by Item 4(c)(i) is set forth in Row 5 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
(ii) Shared power to vote or to direct the vote:
The information required by Item 4(c)(ii) is set forth in Row 6 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
(iii) Sole power to dispose or to direct the disposition of:
The information required by Item 4(c)(iii) is set forth in Row 7 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
(iv) Shared power to dispose or to direct the disposition of:
The information required by Item 4(c)(iv) is set forth in Row 8 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
Item 5.
Ownership of 5 Percent or Less of a Class.
Not Applicable
Item 6.
Ownership of more than 5 Percent on Behalf of Another Person.
If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required.
See Item 2(a). The Sirenia Fund has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, more than 5 percent of the outstanding Common Stock.
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
Not Applicable
Item 8.
Identification and Classification of Members of the Group.
Not Applicable
Item 9.
Notice of Dissolution of Group.
Not Applicable
Item 10.
Certifications:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.
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.
Sirenia Capital Management LP
Signature:
/s/ Kolby Loft
Name/Title:
Kolby Loft, General Counsel & Chief Compliance Officer
How many C4 Therapeutics shares does Sirenia Capital report owning?
They report 23,505,000 shares beneficially associated with Sirenia and Alex Silverstein. The figure includes shares issuable upon exercise of warrants and is shown on the cover page of the filing.
What percentage of C4 Therapeutics does the filing state the reporting persons own?
The filing states 9.9% of the outstanding Common Stock, calculated using 97,578,175 shares outstanding as of February 23, 2026 from the company’s 2025 Form 10-K.
Why can Sirenia not exercise all warrants at once?
Because of a 9.99% Blocker in the Reported Warrants, which prevents exercise to the extent it would cause beneficial ownership to exceed 9.99% of outstanding shares.
How many shares are issuable upon exercise of the reported warrants?
The filing includes 14,170,000 shares issuable upon exercise of the Reported Warrants, a number shown in the cover-page disclosure and Item 4 explanatory text.
Does the filing disclose who receives proceeds if shares are sold?
The filing identifies the Sirenia Fund as the holder with rights to dividends and proceeds; specific cash-flow treatment of future sales is not described in the excerpt.
