# AN-2026-0831: uvicorn 0.50.0 (Jul 4, 2026): --ws auto defaults to websockets-sansio; legacy --ws websockets emits UvicornDeprecationWarning

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- id: AN-2026-0831 (version 1; cite https://breakwire.org/claim/AN-2026-0831/v/1)
- kind: deprecation · status: active · review: editor
- source: <https://github.com/Kludex/uvicorn/blob/0.50.0/uvicorn/protocols/websockets/websockets_impl.py#:~:text=websockets%20implementation%20is%20deprecated>
- more sources: <https://raw.githubusercontent.com/Kludex/uvicorn/0.50.0/uvicorn/protocols/websockets/websockets_impl.py> <https://uvicorn.dev/release-notes/#0500-july-4-2026> <https://raw.githubusercontent.com/Kludex/uvicorn/master/docs/release-notes.md>
- event date: 2026-07-04
- services: uvicorn, python, fastapi
- affected: pypi:uvicorn >=0.50.0
- 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. uvicorn 0.50.0 (July 4, 2026) release notes: --ws auto now picks the websockets-sansio implementation; the legacy websockets implementation is deprecated (#2985).  [✓0 ✗0]
1. Importing uvicorn.protocols.websockets.websockets_impl on uvicorn 0.54.0 emits UvicornDeprecationWarning: "The `websockets` implementation is deprecated, and `--ws websockets` will point at the `websockets-sansio` implementation in a future release. Use `--ws websockets-sansio` or `--ws auto` to switch now." Reproduced 2026-11-04.  [✓0 ✗0]

## Fix
```text
Prefer `--ws auto` (default) or `--ws websockets-sansio`. Pin `--ws websockets` only as a short-term bridge.
```

## Error signatures
- substring: `The 'websockets' implementation is deprecated, and '--ws websockets' will point at the` (uvicorn 0.50.0+/0.54.0 websockets_impl.py UvicornDeprecationWarning; reproduced 2026-11-04)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0831/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary sources opened 2026-11-04 (uvicorn source + release notes; Alembic changelog; unique source_url fragments)