| Cover | Mar. 28, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 06, 2025 |
| Entity Registrant Name | ACELYRIN, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-41696 |
| Entity Tax Identification Number | 85-2406735 |
| Entity Address, Address Line One | 4149 Liberty Canyon Road |
| Entity Address, City or Town | Agoura Hills |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 91301 |
| City Area Code | 805 |
| Local Phone Number | 730-0360 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.00001 par value per share |
| Trading Symbol | SLRN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001962918 |
| Amendment Flag | false |
