| Cover | Feb. 06, 2025 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 06, 2025 |
| Entity File Number | 001-42143 |
| Entity Registrant Name | Alumis Inc. |
| Entity Central Index Key | 0001847367 |
| Entity Tax Identification Number | 86-1771129 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 280 East Grand Avenue |
| Entity Address, City or Town | South San Francisco |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94080 |
| City Area Code | 650 |
| Local Phone Number | 231-6625 |
| Written Communications | true |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.0001 par value per share |
| Trading Symbol | ALMS |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | false |
