urllib3 Support `Content-Encoding: x-gzip` (Fix)

The Fix

pip install urllib3==2.1.0

Based on closed urllib3/urllib3 issue #3174 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Open PR/Commit

@@ -0,0 +1 @@
@@ -0,0 +1 @@
+Fixed decoding Gzip-encoded responses which specified ``x-gzip`` content-encoding.
diff --git a/src/urllib3/response.py b/src/urllib3/response.py
index 367ccfe425..37936f9397 100644

fix.md

Option A — Upgrade to fixed release\npip install urllib3==2.1.0\nWhen NOT to use: Do not use this fix if you require strict adherence to content encoding standards without exceptions.\n\n

Why This Fix Works in Production

Trigger: I'm using an API that returns a gzipped response, but the reported `Content-Encoding` is `x-gzip` rather than `gzip`, so urllib3 fails to decompress it.
Mechanism: urllib3 fails to decompress responses with 'x-gzip' content encoding due to lack of handling
Why the fix works: Treats 'x-gzip' content encoding as equivalent to 'gzip', allowing urllib3 to decompress responses correctly. (first fixed release: 2.1.0).

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

urllib3 fails to decompress responses with 'x-gzip' content encoding due to lack of handling
Production symptom (often without a traceback): I'm using an API that returns a gzipped response, but the reported `Content-Encoding` is `x-gzip` rather than `gzip`, so urllib3 fails to decompress it.

Proof / Evidence

GitHub issue: #3174
Fix PR: https://github.com/urllib3/urllib3/pull/3176
First fixed release: 2.1.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.71

Discussion

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

Jump to Sources Open on GitHub

“https://github.com/urllib3/urllib3/blob/7d0648b53cf4159e7f3ebb8353cb642942ec93e6/src/urllib3/response.py#L207-L220 could be trivially updated to say, after we get past the MultiDecoder return do a if mode.startswith("x-"):\n\t\tmode = mode[2:] and then we don'”

@sigmavirus24 · 2023-11-02 · source

“FWIW, I don't think it's a good idea to blindly assume that x-foo is the same as foo, since there is no guarantee that will…”

@SpecLad · 2023-11-03 · source

“@jeremycline has submitted a PR for this issue.”

@sethmlarson · 2023-11-03 · source

Failure Signature (Search String)

I'm using an API that returns a gzipped response, but the reported `Content-Encoding` is `x-gzip` rather than `gzip`, so urllib3 fails to decompress it.
Unfortunately, I can't find a public server that would produce such responses, so I can't provide a simple reproducer.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
I'm using an API that returns a gzipped response, but the reported `Content-Encoding` is `x-gzip` rather than `gzip`, so urllib3 fails to decompress it.
Unfortunately, I can't find a public server that would produce such responses, so I can't provide a simple reproducer.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
I'm using an API that returns a gzipped response, but the reported `Content-Encoding` is `x-gzip` rather than `gzip`, so urllib3 fails to decompress it.
Unfortunately, I can't find a public server that would produce such responses, so I can't provide a simple reproducer.

What Broke

Responses with 'x-gzip' content encoding are not decompressed, leading to incorrect data handling.

Why It Broke

urllib3 fails to decompress responses with 'x-gzip' content encoding due to lack of handling

Fix Options (Details)

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

pip install urllib3==2.1.0

When NOT to use: Do not use this fix if you require strict adherence to content encoding standards without exceptions.

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

Fix reference: https://github.com/urllib3/urllib3/pull/3176

First fixed release: 2.1.0

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not use this fix if you require strict adherence to content encoding standards without exceptions.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.

Version Compatibility Table

Version	Status
2.1.0	Fixed

Related Issues

No related fixes found.

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Sources

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