Sec Form 4/A Filing - Smith R Sharon @ OCTAVE SPECIALTY GROUP INC - 2025-09-29

FORM 4/A Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Smith R Sharon 2. Issuer Name and Ticker or Trading Symbol OCTAVE SPECIALTY GROUP INC [ OSG] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Exec VP & Group COO (Last) (First) (Middle) OCTAVE SPECIALTY GROUP, INC., 40 WALL STREET, 55TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 09/29/2025 (Street) NEW YORK, NY10005 4. If Amendment, Date Original Filed (MM/DD/YY) 10/01/2025 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 09/29/2025 C 145,135 ( 1 ) A $ 0 219,842 D Common Stock 09/29/2025 F 70,680 ( 2 ) D $ 9.72 149,162 D Common Stock 09/30/2025 M 3,235 ( 3 ) A $ 0 152,397 D Common Stock 09/30/2025 F 3,235 ( 4 ) D $ 8.34 149,162 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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 7. Title and Amount of Underlying Securities (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 of Derivative Security: 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 Deferred Share Units ( 5 ) 09/29/2025 C 145,135 ( 1 ) ( 1 ) Common Stock 145,135 $ 0 0 D Deferred Share Units ( 5 ) 09/30/2025 A 76,206 ( 6 ) ( 6 ) Common Stock 76,206 $ 0 76,206 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Smith R Sharon OCTAVE SPECIALTY GROUP, INC. 40 WALL STREET, 55TH FLOOR NEW YORK, NY10005 Exec VP & Group COO Signatures William White, attorney-in-fact 03/03/2026 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Upon the closing of the sale of Ambac Assurance Corporation by Ambac Financial Group to an entity owned by funds managed by Oaktree Capital Management, L.P., a change of control was triggered causing the Reporting Person's Deferred Share Units ("DSUs") to vest and settle. ( 2 )Represents the corrected amount of DSUs that were converted into shares of common stock and withheld by the Company to satisfy certain tax withholding obligations. ( 3 )On September 30, 2025 the Compensation Committee of the Board of Directors of Ambac Financial Group approved the acceleration of the Reporting Person's 2023 and 2024 Performance Stock Unit awards in connection with the change of control referred to in footnote 1. The reporting person acquired shares of common stock of Ambac Financial Group, Inc. (the "Company") upon the simultaneous vesting and settlement of the reporting person's 2023 and 2024 Long Term Incentive Plan PSU awards. ( 4 )Represents the corrected aggregate amount of PSUs that were converted into shares of common stock and withheld by the Company to satisfy certain tax withholding obligations. ( 5 )Each DSU represents a contingent right to receive one share of common stock of the Company. ( 6 )Represents the aggregate amount of performance stock units ("PSUs") that were converted into an equivalent number of DSUs pursuant to the Company's Executive Stock Deferral Plan, which was designed to enable participants to elect to defer the settlement and income taxation of PSU and restricted stock unit awards in accordance with Section 409A of the Internal Revenue Code of 1986, as amended.

Remarks: This amended Form 4 was filed to correct an error in the calculation of the number of shares required to be withheld by the Company to satisfy certain tax withholding obligations.

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).

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