| Document and Entity Information | Nov. 05, 2024 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001786205 |
| Document Type | 8-K |
| Document Period End Date | Nov. 05, 2024 |
| Entity Registrant Name | Arcellx, Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-41259 |
| Entity Tax Identification Number | 47-2855917 |
| Entity Address, Address Line One | 800 Bridge Parkway |
| Entity Address, City or Town | Redwood City |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94065 |
| City Area Code | (240) |
| Local Phone Number | 327-0630 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.001 par value per share |
| Trading Symbol | ACLX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
