{"cik":1782303,"taxonomy":"us-gaap","tag":"ShareBasedCompensation","label":"Share-based Payment Arrangement, Noncash Expense","description":"Amount of noncash expense for share-based payment arrangement.","entityName":"BOUNDLESS BIO, INC.","units":{"USD":[{"start":"2023-01-01","end":"2023-03-31","val":615000,"accn":"0000950170-24-058188","fy":2024,"fp":"Q1","form":"10-Q","filed":"2024-05-13","frame":"CY2023Q1"},{"start":"2023-01-01","end":"2023-06-30","val":1542000,"accn":"0000950170-24-095421","fy":2024,"fp":"Q2","form":"10-Q","filed":"2024-08-12"},{"start":"2023-01-01","end":"2023-09-30","val":2425000,"accn":"0000950170-24-123291","fy":2024,"fp":"Q3","form":"10-Q","filed":"2024-11-07"},{"start":"2023-01-01","end":"2023-12-31","val":3336000,"accn":"0000950170-25-045725","fy":2024,"fp":"FY","form":"10-K","filed":"2025-03-27","frame":"CY2023"},{"start":"2024-01-01","end":"2024-03-31","val":1328000,"accn":"0000950170-24-058188","fy":2024,"fp":"Q1","form":"10-Q","filed":"2024-05-13"},{"start":"2024-01-01","end":"2024-03-31","val":1328000,"accn":"0000950170-25-067496","fy":2025,"fp":"Q1","form":"10-Q","filed":"2025-05-09","frame":"CY2024Q1"},{"start":"2024-01-01","end":"2024-06-30","val":3463000,"accn":"0000950170-24-095421","fy":2024,"fp":"Q2","form":"10-Q","filed":"2024-08-12"},{"start":"2024-01-01","end":"2024-06-30","val":3463000,"accn":"0000950170-25-102391","fy":2025,"fp":"Q2","form":"10-Q","filed":"2025-08-05"},{"start":"2024-01-01","end":"2024-09-30","val":5508000,"accn":"0000950170-24-123291","fy":2024,"fp":"Q3","form":"10-Q","filed":"2024-11-07"},{"start":"2024-01-01","end":"2024-09-30","val":5508000,"accn":"0001193125-25-265714","fy":2025,"fp":"Q3","form":"10-Q","filed":"2025-11-05"},{"start":"2024-01-01","end":"2024-12-31","val":7516000,"accn":"0000950170-25-045725","fy":2024,"fp":"FY","form":"10-K","filed":"2025-03-27"},{"start":"2024-01-01","end":"2024-12-31","val":7516000,"accn":"0001193125-26-097543","fy":2025,"fp":"FY","form":"10-K","filed":"2026-03-09","frame":"CY2024"},{"start":"2025-01-01","end":"2025-03-31","val":1797000,"accn":"0000950170-25-067496","fy":2025,"fp":"Q1","form":"10-Q","filed":"2025-05-09"},{"start":"2025-01-01","end":"2025-03-31","val":1797000,"accn":"0001193125-26-213321","fy":2026,"fp":"Q1","form":"10-Q","filed":"2026-05-08","frame":"CY2025Q1"},{"start":"2025-01-01","end":"2025-06-30","val":3490000,"accn":"0000950170-25-102391","fy":2025,"fp":"Q2","form":"10-Q","filed":"2025-08-05"},{"start":"2025-01-01","end":"2025-09-30","val":4793000,"accn":"0001193125-25-265714","fy":2025,"fp":"Q3","form":"10-Q","filed":"2025-11-05"},{"start":"2025-01-01","end":"2025-12-31","val":6125000,"accn":"0001193125-26-097543","fy":2025,"fp":"FY","form":"10-K","filed":"2026-03-09","frame":"CY2025"},{"start":"2026-01-01","end":"2026-03-31","val":1371000,"accn":"0001193125-26-213321","fy":2026,"fp":"Q1","form":"10-Q","filed":"2026-05-08","frame":"CY2026Q1"}]}}