The Fix
Upgrade to version 0.13.0 or later.
Based on closed encode/httpx issue #724 · 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%.
@@ -4,6 +4,35 @@ All notable changes to this project will be documented in this file.
The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
+## 0.11.0 (January 9th, 2019)
+
+The 0.11 release reintroduces our sync support, so that `httpx` now supports both a standard thread-concurrency API, and an async API.
fix.md
Option A — Upgrade to fixed release\nUpgrade to version 0.13.0 or later.\nWhen NOT to use: This fix is not suitable for users who require a fully asynchronous API without any synchronous components.\n\n
Why This Fix Works in Production
- Trigger: - Network connection errors are wrapped in `httpx.NetworkError`, rather than exposing lower-level exception types directly.
- Mechanism: The 0.11.0 release reintroduces sync support for the httpx library, allowing both synchronous and asynchronous API usage.
- Why the fix works: The 0.11.0 release reintroduces sync support for the httpx library, allowing both synchronous and asynchronous API usage. (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
- Production symptom (often without a traceback): - Network connection errors are wrapped in `httpx.NetworkError`, rather than exposing lower-level exception types directly.
Proof / Evidence
- GitHub issue: #724
- Fix PR: https://github.com/encode/httpx/pull/737
- 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: 0.63
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Still itching for httpx-native Retry functionality as a 1.0 API feature...”
“Dropping #678, #723 since they're not really a hard requirement here.”
“I think the breaking in this release should not be underestimated from a user perspective”
“Things we could potentially could defer, pass-on, or mitigate: #678, #723”
Failure Signature (Search String)
- - Network connection errors are wrapped in `httpx.NetworkError`, rather than exposing lower-level exception types directly.
- - The per-request `cert`, `verify`, and `trust_env` arguments are escalated from raising errors if used, to no longer being available. These arguments should be used on a
Copy-friendly signature
signature.txt
Failure Signature
-----------------
- Network connection errors are wrapped in `httpx.NetworkError`, rather than exposing lower-level exception types directly.
- The per-request `cert`, `verify`, and `trust_env` arguments are escalated from raising errors if used, to no longer being available. These arguments should be used on a per-client instance instead, or in the top-level API.
Error Message
Signature-only (no traceback captured)
error.txt
Error Message
-------------
- Network connection errors are wrapped in `httpx.NetworkError`, rather than exposing lower-level exception types directly.
- The per-request `cert`, `verify`, and `trust_env` arguments are escalated from raising errors if used, to no longer being available. These arguments should be used on a per-client instance instead, or in the top-level API.
What Broke
Users experienced confusion and potential errors due to the reintroduction of synchronous API after previous async-only versions.
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 suitable for users who require a fully asynchronous API without any synchronous components.
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Option D — Guard side-effects with OnceOnly Guardrail for side-effects
Mitigate duplicate external side-effects under retries/timeouts/agent loops by gating the operation before calling external systems.
- Place OnceOnly between your code/agent and real side-effects (Stripe, emails, CRM, APIs).
- Use a stable key per side-effect (e.g., customer_id + action + idempotency_key).
- Fail-safe: configure fail-open vs fail-closed based on blast radius and spend risk.
Show example snippet (optional)
onceonly.py
from onceonly import OnceOnly
import os
once = OnceOnly(api_key=os.environ["ONCEONLY_API_KEY"], fail_open=True)
# Stable idempotency key per real side-effect.
# Use a request id / job id / webhook delivery id / Stripe event id, etc.
event_id = "evt_..." # replace
key = f"stripe:webhook:{event_id}"
res = once.check_lock(key=key, ttl=3600)
if res.duplicate:
return {"status": "already_processed"}
# Safe to execute the side-effect exactly once.
handle_event(event_id)
When NOT to use: Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.
Fix reference: https://github.com/encode/httpx/pull/737
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 suitable for users who require a fully asynchronous API without any synchronous components.
- Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.
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.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.