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ORGANIZATION AND DESCRIPTION OF BUSINESS (Details) - USD ($) $ in Thousands |  | 9 Months Ended | 34 Months Ended |
--- | --- | --- | --- | ---
Jun. 24, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Jun. 23, 2024 | Dec. 31, 2024
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |
Cash funding received from Illumina |  | $ 0 | $ 1,244,300 |  |
Cash and cash equivalents |  | 126,892 | $ 853,551 |  | $ 214,234
Short-term marketable securities |  | $ 413,238 |  |  | $ 549,236
Illumina, Inc. |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |
Cash funding received from Illumina | $ 932,300 |  |  |  |
Illumina, Inc. |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |
Percent of shares distributed in spin-off (as a percent) | 85.50% |  |  |  |
Stockholders' equity note, spinoff transaction, number of shares distributed (in shares) | 31,000,000.0 |  |  |  |
SDG Ops, LLC | Illumina, Inc. |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |
Percentage ownership prior to spin-off (as a percent) |  |  |  | 100.00% |
Grail, Inc. | Illumina, Inc. |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |
Shares owned (in shares) | 4,502,126 |  |  |  |
Percentage of shares retained after spin-off (as a percent) | 14.50% | 12.50% |  |  |

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