# AN-2026-0798: FastAPI 0.146.0 (Oct 18, 2026): FastAPI(root_path=...) deprecated: "The `root_path` parameter is deprecated. Configure the server's root path instead"

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- id: AN-2026-0798 (version 1; cite https://breakwire.org/claim/AN-2026-0798/v/1)
- kind: deprecation · status: active · review: editor
- source: <https://fastapi.tiangolo.com/release-notes/#:~:text=Deprecate%20the%20root_path%20parameter%20in%20FastAPI>
- more sources: <https://github.com/fastapi/fastapi/blob/0.162.0/fastapi/applications.py#L938-L945> <https://pypi.org/project/fastapi/0.146.0/>
- event date: 2026-10-18
- services: fastapi, python
- affected: pypi:fastapi >=0.146.0
- 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), 0.146.0 (2026-10-18) Breaking Changes: the root_path parameter in FastAPI() is deprecated; configure the server with fastapi run --root-path /api/v1 instead.  [✓0 ✗0]
1. FastAPI source (0.162.0 applications.py) warns with FastAPIDeprecationWarning "The `root_path` parameter is deprecated. Configure the server's root path instead, for example with `fastapi run --root-path /api/v1`." - reproduced 2026-11-04 with FastAPI(root_path='/api').  [✓0 ✗0]

## Fix
```text
Remove `root_path=` from `FastAPI(...)` and set it on the server: `fastapi run --root-path /api/v1` or `uvicorn main:app --root-path /api/v1` (or have the proxy send the prefix). The warning does not break the app unless tests run with warnings as errors.
```

## Error signatures
- substring: `The 'root_path' parameter is deprecated. Configure the server's root path instead` (fastapi/applications.py docstring + warnings.warn (0.162.0); reproduced)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0798/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)