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REVENUE FROM CONTRACTS WITH CUSTOMERS - Narrative (Details) |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
Dec. 03, 2024 USD ($) performanceObligation | Dec. 12, 2021 USD ($) | Jul. 31, 2025 USD ($) | Feb. 28, 2025 USD ($) | Sep. 30, 2025 USD ($) | Sep. 30, 2024 USD ($) | Mar. 31, 2022 USD ($) | Sep. 30, 2025 USD ($) | Sep. 30, 2024 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2024 USD ($)
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  | $ 14,262,000 | $ 388,000 |  | $ 243,676,000 | $ 508,000 |  |
Accounts receivable |  |  |  |  | 3,492,000 |  |  | 3,492,000 |  |  | $ 2,742,000
License revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  | 10,000,000 | 0 |  | 205,355,000 | 0 |  |
Takeda Pharmaceuticals U.S.A., Inc. | License revenue |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Upfront license fee | $ 200,000,000.0 |  |  |  |  |  |  |  |  |  |
Reimbursement from limited partnership investment | 51,400,000 |  |  |  |  |  |  |  |  |  |
Revenue, remaining performance obligation, variable consideration |  |  |  |  | 34,900,000 |  |  | 34,900,000 |  |  |
Takeda Pharmaceuticals U.S.A., Inc. | License and Know-How |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Upfront license fee | 195,400,000 |  |  |  |  |  |  |  |  |  |
Takeda Pharmaceuticals U.S.A., Inc. | Transition Services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Upfront license fee | $ 56,100,000 |  |  |  |  |  |  |  |  |  |
Hansoh Agreement | Hansoh Shanghai Healthtech Co Ltd |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total revenue |  | $ 18,000,000.0 |  |  |  |  | $ 18,000,000.0 |  |  |  |
Revenue, remaining performance obligation, development milestones, variable consideration |  |  |  |  | 23,500,000 |  |  | 23,500,000 |  |  |
Revenue, remaining performance obligation, sales milestones, variable consideration amount |  |  |  |  | 144,000,000.0 |  |  | $ 144,000,000.0 |  |  |
Upfront license fee |  |  |  |  |  |  |  |  | 3,000,000.0 | $ 20,000,000.0 |
Withholding taxes from upfront fee |  |  |  |  |  |  |  |  | 300,000 | $ 2,000,000.0 |
License Agreement | Maximum |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Term of the TSA | fifteen |  |  |  |  |  |  |  |  |  |
License Agreement | Minimum |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Term of the TSA | six |  |  |  |  |  |  |  |  |  |
License Agreement | Hansoh Shanghai Healthtech Co Ltd |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Expiration period |  |  |  |  |  |  |  | 10 years |  |  |
License Agreement | Takeda Pharmaceuticals U.S.A., Inc. |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  | $ 10,000,000.0 |  |  |  |  | $ 10,000,000.0 |  |  |
Expiration period |  |  |  |  |  |  |  | 10 years |  |  |
License agreement upfront fee |  |  |  | $ 200,000,000.0 |  |  |  |  |  |  |
Potential milestone, development based milestones |  |  |  |  | 80,000,000.0 |  |  | $ 80,000,000.0 |  |  |
Potential milestone payments, commercial-based milestones | $ 280,000,000.0 |  |  |  | 280,000,000.0 |  |  | 280,000,000.0 |  |  |
Potential milestone payments, sales-based milestones | $ 740,000,000.0 |  |  |  | 740,000,000.0 |  |  | 740,000,000.0 |  |  |
Number of performance obligations | performanceObligation | 2 |  |  |  |  |  |  |  |  |  |
Accounts receivable |  |  |  |  | 3,400,000 |  |  | 3,400,000 |  |  | 0
Unearned revenue, current |  |  |  |  | 200,000 |  |  | 200,000 |  |  | $ 0
Tech Transfer Agreement | Manufacturing Technology Transfer Agreement |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Service revenue |  |  |  |  | 0 | 3,500 |  | 100,000 | 100,000 |  |
Supply Agreement | Clinical Product Supply Agreement |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Upfront license fee |  |  |  |  | $ 100,000 | $ 400,000 |  | $ 100,000 | $ 400,000 |  |

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