httpx Rename `concurrency` to `backends`. (Fix)

The Fix

Upgrade to version 0.13.0 or later.

Based on closed encode/httpx issue #659 · 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

@@ -6,7 +6,7 @@
 
 from .auth import Auth, AuthTypes, BasicAuth, FunctionAuth
-from .concurrency.base import ConcurrencyBackend
+from .backends.base import ConcurrencyBackend
 from .config import (

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.13.0 or later.\nWhen NOT to use: This fix is not applicable if the directory structure is intended to remain unchanged.\n\n

Why This Fix Works in Production

Trigger: No immediate production failure, but potential confusion in directory naming could lead to misusage.
Mechanism: Renamed the `concurrency` directory to `backends` for consistency with the Client's argument
Why the fix works: Renamed the `concurrency` directory to `backends` to align with the Client's `backend=...` argument. (first fixed release: 0.13.0).

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

Renamed the `concurrency` directory to `backends` for consistency with the Client's argument
Production symptom (often without a traceback): No immediate production failure, but potential confusion in directory naming could lead to misusage.

Proof / Evidence

GitHub issue: #659
Fix PR: https://github.com/encode/httpx/pull/662
First fixed release: 0.13.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.78

Discussion

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

Jump to Sources Open on GitHub

“I think we should probably rename our concurrency directory to backends, so that it mirrors the backend=... argument on the Client, right?”

Issue thread · issue description · source

Failure Signature (Search String)

No immediate production failure, but potential confusion in directory naming could lead to misusage.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
No immediate production failure, but potential confusion in directory naming could lead to misusage.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
No immediate production failure, but potential confusion in directory naming could lead to misusage.

What Broke

No immediate production failure, but potential confusion in directory naming could lead to misusage.

Why It Broke

Renamed the `concurrency` directory to `backends` for consistency with the Client's argument

Fix Options (Details)

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

Upgrade to version 0.13.0 or later.

When NOT to use: This fix is not applicable if the directory structure is intended to remain unchanged.

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/662

First fixed release: 0.13.0

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

When NOT to Use This Fix

This fix is not applicable if the directory structure is intended to remain unchanged.

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
0.13.0	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.