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Fair Value Measurements (Tables) | 12 Months Ended
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Dec. 31, 2025
Fair Value Disclosures [Abstract] |
Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities | The following table sets forth the carrying amount and fair value of Octave’s financial assets and liabilities as of December 31, 2025 and 2024, including the level within the fair value hierarchy at which fair value measurements are categorized. As required by the Fair Value Measurement Topic of the ASC, financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement.
|  | December 31, 2025: |  | December 31, 2024:
|  | Carrying Amount |  | Total Fair Value |  | Fair Value Measurements Categorized as: |  | Carrying Amount |  | Total Fair Value |  | Fair Value Measurements Categorized as:
Level 1 |  | Level 2 |  | Level 3 |  | Level 1 |  | Level 2 |  | Level 3
Financial assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal obligations |  | $ | 11,590 |  |  | $ | 11,590 |  |  | $ | — |  |  | $ | 11,590 |  |  | $ | — |  |  | $ | 14,083 |  |  | $ | 14,083 |  |  | $ | — |  |  | $ | 14,083 |  |  | $ | — |
Corporate obligations |  | 66,573 |  |  | 66,573 |  |  | — |  |  | 66,573 |  |  | — |  |  | 89,192 |  |  | 89,192 |  |  | — |  |  | 89,192 |  |  | — |
U.S. government obligations |  | 35,424 |  |  | 35,424 |  |  | 35,424 |  |  | — |  |  | — |  |  | 40,995 |  |  | 40,995 |  |  | 40,995 |  |  | — |  |  | — |
Residential mortgage-backed securities |  | 1,597 |  |  | 1,597 |  |  | — |  |  | 1,597 |  |  | — |  |  | 2,446 |  |  | 2,446 |  |  | — |  |  | 2,446 |  |  | — |
Commercial mortgage-backed securities |  | 3,341 |  |  | 3,341 |  |  | — |  |  | 3,341 |  |  | — |  |  | 2,101 |  |  | 2,101 |  |  | — |  |  | 2,101 |  |  | — |
Collateralized debt obligations |  | 1,975 |  |  | 1,975 |  |  | — |  |  | 1,975 |  |  | — |  |  | 3,142 |  |  | 3,142 |  |  | — |  |  | 3,142 |  |  | — |
Other asset-backed securities |  | 1,795 |  |  | 1,795 |  |  | — |  |  | 1,795 |  |  | — |  |  | 5,061 |  |  | 5,061 |  |  | — |  |  | 5,061 |  |  | — |
Fixed maturity securities, pledged as collateral: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short term investments |  | 146,442 |  |  | 146,442 |  |  | 146,442 |  |  | — |  |  | — |  |  | 127,601 |  |  | 127,601 |  |  | 127,601 |  |  | — |  |  | — |
Other investments (1) |  | 24,971 |  |  | 7,454 |  |  | — |  |  | — |  |  | — |  |  | 28,294 |  |  | 7,499 |  |  | — |  |  | — |  |  | — |
Cash, cash equivalents and restricted cash |  | 68,440 |  |  | 68,440 |  |  | 68,440 |  |  | — |  |  | — |  |  | 47,275 |  |  | 47,275 |  |  | 47,275 |  |  | — |  |  | — |
Other assets-Loans |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 3,434 |  |  | 3,434 |  |  | — |  |  | — |  |  | 3,434 |
Total financial assets |  | $ | 362,148 |  |  | $ | 344,631 |  |  | $ | 250,306 |  |  | $ | 86,871 |  |  | $ | — |  |  | $ | 363,624 |  |  | $ | 342,829 |  |  | $ | 215,871 |  |  | $ | 116,025 |  |  | $ | 3,434 |
Financial liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term debt, including accrued interest |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 152,560 |  |  | $ | 152,560 |  |  | $ | — |  |  | $ | — |  |  | $ | 152,560 |
Long term debt, including accrued interest |  | 118,901 |  |  | 121,343 |  |  | — |  |  | — |  |  | 121,343 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Derivative liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FX forward contracts |  | 8 |  |  | 8 |  |  | — |  |  | 8 |  |  | — |  |  | 317 |  |  | 317 |  |  | — |  |  | 317 |  |  | — |
Total financial liabilities |  | $ | 118,909 |  |  | $ | 121,351 |  |  | $ | — |  |  | $ | 8 |  |  | $ | 121,343 |  |  | $ | 152,877 |  |  | $ | 152,877 |  |  | $ | — |  |  | $ | 317 |  |  | $ | 152,560 |
(1)Excluded from the fair value measurement categories in the table above are investment funds of $7,454 and $7,499 as of December 31, 2025 and 2024, respectively, which are measured using NAV as a practical expedient. Also excluded from the fair value measurements in the table above are equity securities with a carrying value of $17,517 and $20,618 as of December 31, 2025 and 2024, respectively, that do not have readily determinable fair values and have carrying amounts determined using the measurement alternative.
Summary of Changes in Level 3 Fair Value Category | The following tables present the changes in the Level 3 fair value category for the periods presented in 2025, 2024 and 2023. Octave classifies financial instruments in Level 3 of the fair value hierarchy when there is reliance on at least one significant unobservable input to the valuation model. In addition to these unobservable inputs, the valuation models for Level 3 financial instruments typically also rely on a number of inputs that are readily observable either directly or indirectly. Thus, the gains and losses presented below include changes in the fair value related to both observable and unobservable inputs.
Level-3 Financial Assets and Liabilities Accounted for at Fair Value |  |  |  |  |  |  |  |
Year Ended |  | December 31, 2025 |  | December 31, 2024 |  | December 31, 2023
|  | Investments |  | Derivatives |  | Total |  | Investments |  | Derivatives |  | Total |  | Investments |  | Derivatives |  | Total
Balance, beginning of period |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 13,920 |  |  | $ | 656 |  |  | $ | 14,576 |  |  | $ | 12,341 |  |  | $ | 935 |  |  | $ | 13,276 |
Total gains/(losses) realized and unrealized: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Included in earnings |  | — |  |  | — |  |  | — |  |  | 6,016 |  |  | (656) |  |  | 5,360 |  |  | — |  |  | (279) |  |  | (279) |
Included in other comprehensive income |  | — |  |  | — |  |  | — |  |  | 125 |  |  |  |  | 125 |  |  | 784 |  |  | — |  |  | 784 |
Purchases |  | — |  |  | — |  |  | — |  |  | — |  |  |  |  | — |  |  | 795 |  |  | — |  |  | 795 |
Issuances |  | — |  |  | — |  |  | — |  |  | — |  |  |  |  | — |  |  | — |  |  | — |  |  | — |
Sales |  | — |  |  | — |  |  | — |  |  | — |  |  |  |  | — |  |  | — |  |  | — |  |  | — |
Settlements |  | — |  |  | — |  |  | — |  |  | (20,061) |  |  |  |  | (20,061) |  |  | — |  |  | — |  |  | — |
Balance, end of period |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 13,920 |  |  | $ | 656 |  |  | $ | 14,576 |
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | (656) |  |  | $ | (656) |  |  | $ | — |  |  | $ | (279) |  |  | $ | (279) |
The amount of total gains/(losses) included in other comprehensive income attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 784 |  |  | $ | — |  |  | $ | 784 |
Summary of Gains and Losses (Realized and Unrealized) Relating to Level 3 Assets and Liabilities Included in Earnings | Gains and losses (realized and unrealized) relating to Level 3 assets and liabilities included in earnings for the affected periods are reported as follows:
|  | Net Investment Income |  |  |  |  |  |  |  | Net Gains (Losses) on Derivative Contracts |
Year Ended December 31, 2025 |  |  |  |  |  |  |  |  |  |  |
Total gains (losses) included in earnings for the period |  | $ | — |  |  |  |  |  |  |  |  | $ | — |  |
Changes in unrealized gains (losses) relating to financial instruments still held at the reporting date |  | — |  |  |  |  |  |  |  |  | — |  |
Year Ended December 31, 2024 |  |  |  |  |  |  |  |  |  |  |
Total gains (losses) included in earnings for the period |  | $ | 6,016 |  |  |  |  |  |  |  |  | $ | (656) |  |
Changes in unrealized gains (losses) relating to financial instruments still held at the reporting date |  | — |  |  |  |  |  |  |  |  | (656) |  |
Year Ended December 31, 2023 |  |  |  |  |  |  |  |  |  |  |
Total gains (losses) included in earnings for the period |  | $ | — |  |  |  |  |  |  |  |  | $ | (278) |  |
Changes in unrealized gains (losses) relating to financial instruments still held at the reporting date |  | — |  |  |  |  |  |  |  |  | (278) |  |

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