The Fix
Upgrade to version 0.13.0 or later.
Based on closed encode/httpx issue #787 · 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%.
@@ -399,6 +399,22 @@ client = httpx.Client(timeout=timeout)
```
+## Pool limit configuration
+
+You can control the connection pool size using the `pool_limits` keyword
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 connection pool limiting feature is not required.\n\n
Why This Fix Works in Production
- Trigger: We'll want to include how the pool timeout ties in too.
- Mechanism: Lack of documentation for connection pool limiting in the HTTPX library
- Why the fix works: Documents the connection pool limiting feature in the HTTPX library, including configuration options and default values. (first fixed release: 0.13.0).
- 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
- Lack of documentation for connection pool limiting in the HTTPX library
- Production symptom (often without a traceback): We'll want to include how the pool timeout ties in too.
Proof / Evidence
- GitHub issue: #787
- Fix PR: https://github.com/encode/httpx/pull/942
- 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: 0.83
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Closed via https://github.com/encode/httpx/pull/942”
“:-1: on limits = (int, int) from me. I much prefer to be explicit, and don't want to remember "Is it the soft limit first,…”
“> We should possible also be dropping the tuple-style on timeout = , then? > Other places where we use this style: Ah! I hadn't…”
“> I much prefer to be explicit, and don't want to remember "Is it the soft limit first, or the hard? Fair comment”
Failure Signature (Search String)
- We'll want to include how the pool timeout ties in too.
- And in the timeout section:
Copy-friendly signature
Failure Signature
-----------------
We'll want to include how the pool timeout ties in too.
And in the timeout section:
Error Message
Signature-only (no traceback captured)
Error Message
-------------
We'll want to include how the pool timeout ties in too.
And in the timeout section:
What Broke
Users are unaware of how to configure connection pool limits, leading to potential performance issues.
Why It Broke
Lack of documentation for connection pool limiting in the HTTPX library
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
Upgrade to version 0.13.0 or later.
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/942
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 connection pool limiting feature is not required.
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.
- Add a TLS smoke test that performs a real handshake in CI (include CA bundle validation and hostname checks).
- Alert on handshake failures by error string and endpoint to catch cert/CA changes quickly.
Version Compatibility Table
| Version | Status |
|---|---|
| 0.13.0 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.