The Fix
Upgrade to version 0.11.4 or later.
Based on closed Kludex/uvicorn issue #89 · PR/commit linked
Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.
@@ -172,6 +172,32 @@ def app(scope):
[email protected]("protocol_cls", [HttpToolsProtocol, H11Protocol])
+def test_pipelined_requests(protocol_cls):
+ def app(scope):
Option A — Upgrade to fixed release\nUpgrade to version 0.11.4 or later.\nWhen NOT to use: This fix should not be used if pipelining is not required or if it introduces unexpected behavior.\n\n
Why This Fix Works in Production
- Trigger: Clients experienced delays and failed requests due to lack of pipelining support.
- Mechanism: Pipelining support was temporarily dropped in the httptools implementation due to lack of request/response cycle management
- Why the fix works: Adds support for HTTP pipelining in the httptools implementation, allowing multiple requests to be handled in a single connection. (first fixed release: 0.11.4).
- If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.
Why This Breaks in Prod
- Pipelining support was temporarily dropped in the httptools implementation due to lack of request/response cycle management
- Production symptom (often without a traceback): Clients experienced delays and failed requests due to lack of pipelining support.
Proof / Evidence
- GitHub issue: #89
- Fix PR: https://github.com/kludex/uvicorn/pull/115
- First fixed release: 0.11.4
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.82
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“We've temporarily dropped pipelining support from the httptools implementation, although everythings in place in order to support it. Need to: Keep track of queued request/response cycles if a new cycle starts before the existing one has fi”
Failure Signature (Search String)
- Clients experienced delays and failed requests due to lack of pipelining support.
Copy-friendly signature
Failure Signature
-----------------
Clients experienced delays and failed requests due to lack of pipelining support.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
Clients experienced delays and failed requests due to lack of pipelining support.
What Broke
Clients experienced delays and failed requests due to lack of pipelining support.
Why It Broke
Pipelining support was temporarily dropped in the httptools implementation due to lack of request/response cycle management
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
Upgrade to version 0.11.4 or later.
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Fix reference: https://github.com/kludex/uvicorn/pull/115
First fixed release: 0.11.4
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix should not be used if pipelining is not required or if it introduces unexpected behavior.
Did This Fix Work in Your Case?
Quick signal helps us prioritize which fixes to verify and improve.
Prevention
- Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
- Pin production dependencies and upgrade only with a reproducible test that hits the failing path.
Version Compatibility Table
| Version | Status |
|---|---|
| 0.11.4 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.