httpx When using proxy the request downgrades to HTTP/1

The Fix

Upgrade to version 0.21.2 or later.

Based on closed encode/httpx issue #1992 · 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%.

Jump to Verify Open PR/Commit

@@ -138,19 +138,36 @@ def __init__(
             )
         else:
-            self._pool = httpcore.HTTPProxy(
-                proxy_url=httpcore.URL(
-                    scheme=proxy.url.raw_scheme,

repro.py

Name: httpx
Version: 0.21.1
Summary: The next generation HTTP client.
Home-page: https://github.com/encode/httpx
Author: Tom Christie
Author-email: [email protected]

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.21.2 or later.\nWhen NOT to use: This fix should not be used if the application requires strict HTTP/1 behavior.\n\n

Why This Fix Works in Production

Trigger: Same problem in httpx 0.21.1. I try the socks5 and http proxy, and they all failed. But I can get normal http2 response via Chrome using proxy. So weird.
Mechanism: The library did not support HTTP/2 for requests made through proxies
Why the fix works: Adds HTTP/2 support for tunnelled proxy cases, addressing the issue where requests downgrade to HTTP/1 when using a proxy. (first fixed release: 0.21.2).

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 library did not support HTTP/2 for requests made through proxies
Production symptom (often without a traceback): Same problem in httpx 0.21.1. I try the socks5 and http proxy, and they all failed. But I can get normal http2 response via Chrome using proxy. So weird.

Proof / Evidence

GitHub issue: #1992
Fix PR: https://github.com/encode/httpx/pull/2009
First fixed release: 0.21.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.69

Discussion

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

Jump to Sources Open on GitHub

“Same problem in httpx 0.21.1. I try the socks5 and http proxy, and they all failed. But I can get normal http2 response via Chrome…”

@knu-code · 2021-12-30 · source

“@yofeng2021 Yes, same with me. I was able to load proxy via chrome and the request went through HTTP/2. I think the issue stands with…”

@biplovdahal · 2021-12-30 · source

Failure Signature (Search String)

Same problem in httpx 0.21.1. I try the socks5 and http proxy, and they all failed. But I can get normal http2 response via Chrome using proxy. So weird.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Same problem in httpx 0.21.1. I try the socks5 and http proxy, and they all failed. But I can get normal http2 response via Chrome using proxy. So weird.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Same problem in httpx 0.21.1. I try the socks5 and http proxy, and they all failed. But I can get normal http2 response via Chrome using proxy. So weird.

Minimal Reproduction

repro.py

Name: httpx
Version: 0.21.1
Summary: The next generation HTTP client.
Home-page: https://github.com/encode/httpx
Author: Tom Christie
Author-email: [email protected]

Environment

httpx: 0.21.1

What Broke

Requests downgraded to HTTP/1 when using a proxy, causing performance issues.

Why It Broke

The library did not support HTTP/2 for requests made through proxies

Fix Options (Details)

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

Upgrade to version 0.21.2 or later.

When NOT to use: This fix should not be used if the application requires strict HTTP/1 behavior.

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

Fix reference: https://github.com/encode/httpx/pull/2009

First fixed release: 0.21.2

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

When NOT to Use This Fix

This fix should not be used if the application requires strict HTTP/1 behavior.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

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
0.21.2	Fixed

Related Issues

No related fixes found.

Cluster: httpx:configuration-error All hubs All clusters

Related clusters: Data consistency Other Timeout

Sources

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

httpx When using proxy the request downgrades to HTTP/1 (Fix)