# AN-2026-0799: FastAPI 0.131.0 (Feb 22, 2026): ORJSONResponse and UJSONResponse deprecated: "ORJSONResponse is deprecated, FastAPI now serializes data directly to JSON bytes via Pydantic"

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- id: AN-2026-0799 (version 1; cite https://breakwire.org/claim/AN-2026-0799/v/1)
- kind: deprecation · status: active · review: editor
- source: <https://fastapi.tiangolo.com/release-notes/#:~:text=Deprecate%20ORJSONResponse%20and%20UJSONResponse>
- more sources: <https://github.com/fastapi/fastapi/blob/0.162.0/fastapi/responses.py#L39-L80> <https://pypi.org/project/fastapi/0.131.0/>
- event date: 2026-02-22
- services: fastapi, python
- affected: pypi:fastapi >=0.131.0
- severity: low
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. FastAPI release notes (opened 2026-11-04): 0.130.0 (2026-02-22) serializes JSON responses with Pydantic (in Rust) when there is a Pydantic return type or response model; 0.131.0 (2026-02-22) Breaking Changes: deprecate ORJSONResponse and UJSONResponse.  [✓0 ✗0]
1. FastAPI source (0.162.0 responses.py) marks both classes @deprecated with FastAPIDeprecationWarning: "ORJSONResponse is deprecated, FastAPI now serializes data directly to JSON bytes via Pydantic when a return type or response model is set ..." (same text for UJSONResponse). Reproduced 2026-11-04: instantiating ORJSONResponse warns, and without orjson installed it then fails with "orjson must be installed to use ORJSONResponse".  [✓0 ✗0]

## Fix
```text
Drop `default_response_class=ORJSONResponse` / `UJSONResponse` and declare a return type or `response_model` so FastAPI serializes via Pydantic; return plain dicts/models. Remove orjson/ujson from requirements if nothing else uses them.
```

## Error signatures
- substring: `ORJSONResponse is deprecated, FastAPI now serializes data directly to JSON` (fastapi/responses.py @deprecated (0.162.0); reproduced)
- substring: `UJSONResponse is deprecated, FastAPI now serializes data directly to JSON` (fastapi/responses.py @deprecated (0.162.0))

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0799/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary sources opened 2026-11-04 (FastAPI release notes + 0.162.0 source, Starlette release notes + 1.10.0 source; messages reproduced on fastapi 0.162.0 / starlette 1.10.0)