uvicorn Having a Hard Time Replacing Default Server Header

The Fix

Upgrade to version 0.11.4 or later.

Based on closed Kludex/uvicorn issue #243 · 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%.

Open PR/Commit

@@ -2,13 +2,13 @@
 import h11
 import pytest
+
+from tests.response import Response
 from uvicorn.config import Config

fix.md

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 the default Server header is required for compliance.\n\n

Why This Fix Works in Production

Trigger: I feel like messing with that will require constant vigilance as the upstream changes.
Mechanism: The default Server header in Uvicorn responses was hardcoded and not configurable
Why the fix works: Merged PR #302 which adds functionality to override the default Server header in Uvicorn responses. (first fixed release: 0.11.4).

Production impact:

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

The default Server header in Uvicorn responses was hardcoded and not configurable
Production symptom (often without a traceback): I feel like messing with that will require constant vigilance as the upstream changes.

Proof / Evidence

GitHub issue: #243
Fix PR: https://github.com/encode/uvicorn/pull/302
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: 0.73

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“> I feel like messing with that will require constant vigilance as the upstream changes. That is true, it's not perfect. Hopefully this issue will…”

@antirais · 2019-03-07 · confirmation · source

“PR has been merged which resolves this issue.”

@Jitsusama · 2019-03-15 · confirmation · source

“I think we should support a -h/--header interface to allow developers to explicitly set particular headers (and to override the default "Server" one) Should all…”

@lovelydinosaur · 2019-02-14 · source

“@tomchristie; that sounds wonderful! Would you also supply an API method/parameter to do this?”

@Jitsusama · 2019-02-14 · source

Failure Signature (Search String)

I feel like messing with that will require constant vigilance as the upstream changes.
Hey @tomchristie; I'm taking a look now. Should tests for this go in `tests/protocols/test_http.py`? I can't find any other place that really makes sense.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
I feel like messing with that will require constant vigilance as the upstream changes.
Hey @tomchristie; I'm taking a look now. Should tests for this go in `tests/protocols/test_http.py`? I can't find any other place that really makes sense.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
I feel like messing with that will require constant vigilance as the upstream changes.
Hey @tomchristie; I'm taking a look now. Should tests for this go in `tests/protocols/test_http.py`? I can't find any other place that really makes sense.

What Broke

Responses always included 'Server: uvicorn' header, limiting customization.

Why It Broke

The default Server header in Uvicorn responses was hardcoded and not configurable

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Upgrade to version 0.11.4 or later.

When NOT to use: This fix should not be used if the default Server header is required for compliance.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/encode/uvicorn/pull/302

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 the default Server header is required for compliance.

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.

Cluster: uvicorn:configuration-error All hubs All clusters

Related clusters: Data consistency Race condition SSL handshake

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

uvicorn Having a Hard Time Replacing Default Server Header (Fix)