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Investments | 12 Months Ended
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Dec. 31, 2024
Investments, Debt and Equity Securities [Abstract] |
Investments | 6. INVESTMENTS Ambac’s invested assets are primarily comprised of (i) fixed maturity securities classified as either available-for-sale, (ii) interests in pooled investment funds which are reported within Other investments on the Consolidated Balance Sheets and (iii) preferred equity investments which are reported within Other investments on the Consolidated Balance Sheets. Interests in pooled investment funds are limited partner interests and are reported using the equity method. Fixed Maturity Securities The amortized cost and estimated fair value of available-for-sale investments, at December 31, 2024 and 2023 were as follows:
|  | December 31, 2024 |  | December 31, 2023
|  | Amortized Cost |  | Allowance for Credit Losses |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Estimated Fair Value |  | Amortized Cost |  | Allowance for Credit Losses |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Estimated Fair Value
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal obligations |  | $ | 14,646 |  |  | $ | — |  |  | $ | 7 |  |  | $ | 570 |  |  | $ | 14,083 |  |  | $ | 9,394 |  |  | — |  |  | 13 |  |  | 696 |  |  | 8,711 |
Corporate obligations |  | 92,990 |  |  | — |  |  | 107 |  |  | 3,905 |  |  | 89,192 |  |  | 92,694 |  |  | — |  |  | 262 |  |  | 4,965 |  |  | 87,991 |
U.S. government obligations |  | 41,706 |  |  | — |  |  | 98 |  |  | 809 |  |  | 40,995 |  |  | 39,091 |  |  | — |  |  | 364 |  |  | 933 |  |  | 38,522 |
Residential mortgage-backed securities |  | 2,475 |  |  | — |  |  | — |  |  | 29 |  |  | 2,446 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Commercial mortgage-backed securities |  | 2,127 |  |  | — |  |  | 8 |  |  | 34 |  |  | 2,101 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Collateralized debt obligations |  | 3,131 |  |  | — |  |  | 13 |  |  | 2 |  |  | 3,142 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Other asset-backed securities |  | 5,049 |  |  | — |  |  | 14 |  |  | 2 |  |  | 5,061 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
|  | 162,124 |  |  | — |  |  | 247 |  |  | 5,351 |  |  | 157,020 |  |  | 141,179 |  |  | — |  |  | 639 |  |  | 6,594 |  |  | 135,224 |
Short-term |  | 127,588 |  |  | — |  |  | 13 |  |  | — |  |  | 127,601 |  |  | 200,506 |  |  | — |  |  | 4 |  |  | — |  |  | 200,510 |
Total available-for-sale investments |  | $ | 289,712 |  |  | $ | — |  |  | $ | 260 |  |  | $ | 5,351 |  |  | $ | 284,621 |  |  | 341,685 |  |  | $ | — |  |  | $ | 643 |  |  | $ | 6,594 |  |  | $ | 335,734 |
The amortized cost and estimated fair value of available-for-sale investments, at December 31, 2024, by contractual maturity, were as follows:
|  | Amortized Cost |  | Estimated Fair Value
Due in one year or less |  | $ | 158,357 |  |  | $ | 158,056 |
Due after one year through five years |  | 62,715 |  |  | 61,169 |
Due after five years through ten years |  | 54,882 |  |  | 51,688 |
Due after ten years |  | 976 |  |  | 958 |
|  | 276,930 |  |  | 271,871 |
Residential mortgage-backed securities |  | 2,475 |  |  | 2,446 |
Commercial mortgage-backed securities |  | 2,127 |  |  | 2,101 |
Collateralized debt obligations |  | 3,131 |  |  | 3,142 |
Other asset-backed securities |  | 5,049 |  |  | 5,061 |
Total |  | $ | 289,712 |  |  | $ | 284,621 |
Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay certain obligations with or without call or prepayment penalties. Unrealized Losses on Fixed Maturity Securities The following table shows gross unrealized losses and fair values of Ambac’s available-for-sale investments, which at December 31, 2024, did not have an allowance for credit losses under the CECL standard. This information is aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position, at December 31, 2024 and 2023:
|  | December 31, 2024 |  | December 31, 2023
|  | Less Than 12 Months |  | 12 Months or More |  | Total |  | Less Than 12 Months |  | 12 Months or More |  | Total
|  | Fair Value |  | Gross Unrealized Loss |  | Fair Value |  | Gross Unrealized Loss |  | Fair Value |  | Gross Unrealized Loss |  | Fair Value |  | Gross Unrealized Loss |  | Fair Value |  | Gross Unrealized Loss |  | Fair Value |  | Gross Unrealized Loss
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal obligations |  | $ | 6,042 |  |  | $ | 112 |  |  | $ | 6,582 |  |  | $ | 458 |  |  | $ | 12,624 |  |  | $ | 570 |  |  | $ | 732 |  |  | $ | 17 |  |  | $ | 7,015 |  |  | $ | 679 |  |  | $ | 7,747 |  |  | $ | 696 |
Corporate obligations |  | 23,784 |  |  | 269 |  |  | 46,612 |  |  | 3,636 |  |  | 70,396 |  |  | 3,905 |  |  | 12,134 |  |  | 49 |  |  | 59,010 |  |  | 4,916 |  |  | 71,144 |  |  | 4,965 |
U.S. government obligations |  | 15,919 |  |  | 344 |  |  | 14,818 |  |  | 465 |  |  | 30,737 |  |  | 809 |  |  | 6,847 |  |  | 37 |  |  | 20,981 |  |  | 896 |  |  | 27,828 |  |  | 933 |
Residential mortgage-backed securities |  | 2,446 |  |  | 29 |  |  | — |  |  | — |  |  | 2,446 |  |  | 29 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Commercial mortgage-backed securities |  | 738 |  |  | 34 |  |  | — |  |  | — |  |  | 738 |  |  | 34 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Collateralized debt obligations |  | 655 |  |  | 2 |  |  | — |  |  | — |  |  | 655 |  |  | 2 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Other asset-backed securities |  | 1,428 |  |  | 2 |  |  | — |  |  | — |  |  | 1,428 |  |  | 2 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
|  | 51,012 |  |  | 792 |  |  | 68,012 |  |  | 4,559 |  |  | 119,024 |  |  | 5,351 |  |  | 19,713 |  |  | 103 |  |  | 87,006 |  |  | 6,491 |  |  | 106,719 |  |  | 6,594 |
Short-term |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 619 |  |  | — |  |  | — |  |  | — |  |  | 619 |  |  | — |
Total temporarily impaired securities |  | $ | 51,012 |  |  | $ | 792 |  |  | $ | 68,012 |  |  | $ | 4,559 |  |  | $ | 119,024 |  |  | $ | 5,351 |  |  | $ | 20,332 |  |  | $ | 103 |  |  | $ | 87,006 |  |  | $ | 6,491 |  |  | $ | 107,338 |  |  | $ | 6,594 |
Management has determined that the securities in the above table do not have credit impairment as of December 31, 2024 and 2023 based upon (i) no actual or expected principal and interest payment defaults on these securities and (ii) analysis of the creditworthiness of the issuer. Ambac’s assessment about whether a security is credit impaired reflects management’s current judgment regarding facts and circumstances specific to the security and other factors. If that judgment changes, Ambac may record a charge for credit impairment in future periods. The declines in fair value and resultant unrealized losses across asset classes as of December 31, 2024, included in the above table resulted primarily from the impact of increasing interest rates since the securities were purchased. Management has determined that the securities with unrealized losses are not credit impaired. Further discussion of management's assessment with respect to security categories with larger unrealized loss balances is below. Corporate obligations The gross unrealized losses on corporate obligations as of December 31, 2024, resulted primarily from an increase in interest rates since the securities were purchased. Unrealized losses of $3,905 related to 145 investment grade securities with an average unrealized loss equal to 5% of amortized cost at December 31, 2024. Securities that have below investment grade credit ratings or are unrated comprise $0 of the gross unrealized loss at December 31, 2024. Management believes that the full and timely receipt of all principal and interest payment on corporate obligations with unrealized losses as of December 31, 2024, is probable. Investment Income (Loss) Net investment income (loss) was comprised of the following for the affected periods:
Year Ended December 31, |  | 2024 |  | 2023 |  | 2022
Fixed maturity securities |  | $ | 4,895 |  |  | $ | 3,696 |  |  | $ | 2,163 |
Short-term investments |  | 10,033 |  |  | 9,287 |  |  | 2,345 |
Investment expense |  | (365) |  |  | (296) |  |  | (139) |
Securities available-for-sale and short-term |  | 14,563 |  |  | 12,687 |  |  | 4,369 |
Fixed maturity securities - trading |  | — |  |  | — |  |  | — |
Other investments |  | (115) |  |  | 472 |  |  | 134 |
Total net investment income (loss) |  | $ | 14,448 |  |  | $ | 13,159 |  |  | $ | 4,503 |
Net investment income (loss) from Other investments primarily represents changes in fair value on equity securities including certain pooled investment funds, and income from investment limited partnerships and other equity interests accounted for under the equity method. Net Investments Gains (Losses), including Impairments The following table details amounts included in net investment gains (losses) and impairments included in earnings for the affected periods:
Year Ended December 31, |  | 2024 |  | 2023 |  | 2022
Gross realized gains on securities |  | $ | 6,020 |  |  | $ | 57 |  |  | $ | 43 |
Gross realized losses on securities |  | (1) |  |  | (38) |  |  | (105) |
Foreign exchange (losses) gains |  | — |  |  | — |  |  | — |
Credit impairments |  | (6,516) |  |  | — |  |  | — |
Intent to sell impairments |  | — |  |  | — |  |  | — |
Net investment gains (losses), including impairments |  | $ | (497) |  |  | $ | 19 |  |  | $ | (62) |
Ambac had an allowance for credit losses $0 and $0 at December 31, 2024 and 2023, respectively. Ambac did not purchase any financial assets with credit deterioration for the years ended December 31, 2024 and 2023. Deposits with Regulators and Other Restrictions Securities carried at $22,861 and $20,748 at December 31, 2024 and 2023, respectively, were deposited by Ambac's insurance subsidiaries with governmental authorities or designated custodian banks as required by laws affecting insurance companies. Invested assets of AAC carried at $800 and reported within assets held-for-sale on Ambac's consolidated balance sheet as of December 31, 2024, were deposited as security in connection with a letter of credit issued for a corporate office lease. The lease will be transferred to Ambac in connection with the AAC sale. Fiduciary funds held by Ambac's insurance distribution subsidiaries, carried at $2,845 and $1,769 at December 31, 2024 and 2023, respectively, are included in invested assets. Other Investments Ambac's investment portfolio includes a limited partnership interest in a private equity fund which seeks to generate long-term capital appreciation through investments in private equity, equity-related and other instruments. The fair value of Ambac's investment in the fund was $7,499 and $5,817 as of December 31, 2024 and 2023, determined using net asset value ("NAV") as a practical expedient. Redemptions may be made quarterly with 90 days notice subject to withdrawal limitations and/or redemption fees which vary with the timing and notification of withdrawal provided by the investor. Ambac's unfunded commitments total $1,724 on this private equity fund at December 31, 2024. Other investments also include preferred equity investments with a carrying value of $20,618 and $12,500 as of December 31, 2024 and 2023, respectively, that do not have readily determinable fair values and are carried at cost, less any impairments as permitted under the Investments — Equity Securities Topic of the ASC. Impairments of $6,516, $0, and $0 were recorded on these investments in the years ended December 31, 2024, 2023 and 2022, respectively. There were no adjustments to fair value to reflect observable price changes in identical or similar investments from the same issuer during the years ended December 31, 2024, 2023 and 2022.
Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities |

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