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Commitments and Contingent Liabilities - Operating Leases (Details) | 1 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2024 ft² | Jul. 31, 2023 USD ($) ft² | Jan. 31, 2023 USD ($) ft² | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | Sep. 30, 2025 USD ($) | Jan. 31, 2025 USD ($) | Aug. 31, 2022 USD ($) ft²
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Lease space | ft² | 22,000 |  |  |  |  |  |  | 55,000
Tenant improvement allowance provided by lessor |  |  |  |  |  |  |  | $ 17,200,000
Tenant improvement allowance received |  |  |  | $ 16,700,000 | $ 500,000 |  |  |
Future lease payments |  |  | $ 37,900,000 |  |  | $ 54,879,000 | $ 1,900,000 |
Gross fixed payments |  |  | 54,600,000 |  |  |  |  |
Lease incentives receivable |  |  | 16,700,000 |  |  |  |  | $ 16,700,000
Lease liability |  |  | $ 14,100,000 |  |  | $ 37,797,000 | $ 1,800,000 |
Weighted-average incremental borrowing rate | 11.40% |  | 11.40% |  |  | 11.60% | 7.90% |
Renewal term |  |  |  |  |  |  |  | 3 years
Lessee, Operating Lease, Lease Not yet Commenced, Existence of Option to Extend [true false] | true |  |  |  |  |  |  |
Lease not yet commenced, renewal term | 2 years |  |  |  |  |  |  |
ACELYRIN |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Lease space | ft² |  | 22,365 | 10,012 |  |  |  |  |
Term of lease |  | 60 months | 65 months |  |  |  |  |
Renewal term |  | 5 years | 3 years |  |  |  |  |
Monthly rent payments |  | $ 150,000 | $ 30,500 |  |  |  |  |
Percentage increase in monthly rent payments |  | 3.50% | 3.00% |  |  |  |  |

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