FastAPI 0.149.0–0.151.0 stable releases change empty forms, files and JSON null

GitHub releases and PyPI uploads are confirmed. Version 0.149.0 treats empty scalar values in form models as missing; 0.150.0 treats unselected file inputs as missing. Named zero-byte files remain valid. Version 0.151.0 distinguishes explicit JSON null from omission: omit a value to request its default. Review input validation and code relying on defaults before upgrading.

Announced2026-10-20