# Uvicorn 0.52.1 — Version 0.52.1

- Product: Uvicorn (https://whatsnew.fyi/product/uvicorn)
- Vendor: Encode
- Date: 2026-08-01
- Version: 0.52.1
- Original notes: https://github.com/Kludex/uvicorn/releases/tag/0.52.1
- Permalink: https://whatsnew.fyi/product/uvicorn/releases/0.52.1

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

---

- **fixed** — Complete the closing handshake on server-initiated WebSocket closes in the websockets-sansio and wsproto implementations, waiting for the client's close reply with a 10 second timeout instead of resetting the connection
- **fixed** — Add missing write flow control to the websockets-sansio implementation, preventing data truncation on server-initiated closes with large in-flight payloads
- **fixed** — Handle connection loss while a WebSocket write is waiting on backpressure
- **fixed** — Remove duplicate Content-Type and Content-Length headers from WebSocket denial responses on the websockets-sansio implementation, and deliver non-UTF-8 denial bodies intact

###### Fixed

* Complete the closing handshake on server-initiated WebSocket closes in the `websockets-sansio` and `wsproto` implementations, waiting for the client's close reply with a 10 second timeout instead of resetting the connection (#3053)
* Add missing write flow control to the `websockets-sansio` implementation, preventing data truncation on server-initiated closes with large in-flight payloads (#3048)
* Handle connection loss while a WebSocket write is waiting on backpressure (#3050)
* Remove duplicate `Content-Type` and `Content-Length` headers from WebSocket denial responses on the `websockets-sansio` implementation, and deliver non-UTF-8 denial bodies intact (#3041)

**Full Changelog**: https://github.com/Kludex/uvicorn/compare/0.52.0...0.52.1