# AN-2026-0797: FastAPI 0.145/0.155 (Oct 18-20, 2026): openapi_prefix and the deprecated **extra kwargs on Query/Path/Header/Cookie/Body/Form/File removed; unknown kwargs raise TypeError

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- id: AN-2026-0797 (version 1; cite https://breakwire.org/claim/AN-2026-0797/v/1)
- kind: breaking · status: active · review: editor
- source: <https://fastapi.tiangolo.com/release-notes/#:~:text=Remove%20deprecated%20**extra%20from%20request%20parameters>
- more sources: <https://fastapi.tiangolo.com/release-notes/#:~:text=Remove%20deprecated%20openapi_prefix> <https://pypi.org/project/fastapi/0.155.0/>
- event date: 2026-10-20
- services: fastapi, python
- affected: pypi:fastapi >=0.145.0
- severity: medium
- 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): 0.155.0 (2026-10-20) removed the deprecated **extra keyword arguments from Path, Query, Header, Cookie, Body, Form and File; unknown keyword arguments now raise TypeError; for additional JSON Schema properties replace e.g. Query(custom="value") with Query(json_schema_extra={"custom": "value"}). 0.145.0 (2026-10-18) removed the deprecated openapi_prefix and unused **extra from FastAPI.  [✓0 ✗0]
1. Reproduced 2026-11-04 with fastapi 0.162.0: Query(custom='v') raises TypeError "Query() got an unexpected keyword argument 'custom'", Body(example_x=1) raises "Body() got an unexpected keyword argument 'example_x'", and FastAPI(openapi_prefix='/x') raises "FastAPI.__init__() got an unexpected keyword argument 'openapi_prefix'".  [✓0 ✗0]

## Fix
```text
Move custom schema keys into `json_schema_extra={...}` (e.g. `Query(json_schema_extra={"x-internal": True})`); use `examples=[...]` instead of ad-hoc example kwargs. Replace `openapi_prefix` with a server root path (`fastapi run --root-path /api/v1` or `uvicorn --root-path`). Or pin `fastapi<0.145`.
```

## Outcome reports (0)
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## 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)