X0609 4 2026-10-03 0 0000874501 OCTAVE SPECIALTY GROUP INC OSG 0001380820 LeBlanc Claude false C/O OCTAVE SPECIALTY GROUP, INC. 40 WALL STREET, 55TH FLOOR NEW YORK NY 10005 1 1 0 0 Chief Executive Officer 0 Common Stock 2026-10-03 4 M 0 15229 A 1080463 D Common Stock 2026-10-03 4 F 0 8421 4.60 D 1072042 D Common Stock 2026-10-03 4 M 0 11628 A 1083670 D Common Stock 2026-10-03 4 F 0 11638 4.60 D 1072032 D Restricted Stock Units 2026-10-03 4 M 0 15229 0 D Common Stock 15229 465603 D Restricted Stock Units 2026-10-03 4 M 0 232816 0 D Common Stock 232816 232787 D Deferred Share Units 2026-10-03 4 M 0 221188 0 A Common Stock 221188 418731 D The reporting person acquired shares of common stock Octave Specialty Group, Inc. (the "Company") upon the vesting and settlement of a portion of the reporting person's restricted stock unit ("RSU") awards as part of their 2025 Long Term Incentive Plan. Represents the amount of RSUs that were converted into shares of common stock and withheld by the Company to satisfy certain tax withholding obligations. Each RSU represents a contingent right to receive one share of the Company's common stock. Represents the aggregate amount of RSUs that vested. Each deferred share unit ("DSU") represents a contingent right to receive one share of common stock of the Company. Represents the aggregate amount of RSUs 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 RSU and Performance Stock Unit awards in accordance with Section 409A of the Internal Revenue Code of 1986, as amended. Reid Powell, attorney-in-fact 2026-10-06