The Fix
Upgrade to version 0.7.3 or later.
Based on closed encode/httpx issue #256 · 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%.
@@ -0,0 +1,3 @@
@@ -0,0 +1,3 @@
+from .backend import AsyncioBackend, BackgroundManager, PoolSemaphore, TCPStream
+
+__all__ = ["AsyncioBackend", "BackgroundManager", "PoolSemaphore", "TCPStream"]
repro.py
# < 3.8
reader, writer = await asyncio.open_connection('127.0.0.1', 8888)
# 3.8+
async with asyncio.connect('127.0.0.1', 8888) as stream:
...
# or:
stream = await asyncio.connect('127.0.0.1', 8888)
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 0.7.3 or later.\nWhen NOT to use: This fix is not suitable for environments running Python versions below 3.7.\n\n
Why This Fix Works in Production
- Trigger: This is not a trivial API change, and I don't know if there are plans to back-port `asyncio.connect()` to 3.7 and below.
- Mechanism: Adapts the AsyncioBackend to use the new asyncio.Stream API in Python 3.8, addressing deprecation warnings related to StreamReader and StreamWriter.
- Why the fix works: Adapts the AsyncioBackend to use the new asyncio.Stream API in Python 3.8, addressing deprecation warnings related to StreamReader and StreamWriter. (first fixed release: 0.7.3).
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
- Triggered by an upgrade/regression window: 3.8 breaks; 0.7.3 is the first fixed release.
- Shows up under Python 3.8 in real deployments (not just unit tests).
- Production symptom (often without a traceback): Python 3.8 builds are filled with warnings about asyncio API changes: https://travis-ci.org/encode/httpx/jobs/574559125
Proof / Evidence
- GitHub issue: #256
- Fix PR: https://github.com/encode/httpx/pull/369
- First fixed release: 0.7.3
- Affected versions: 3.8
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.75
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.66
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Let’s wait for this to be confirmed and merged on the Python side, then we can open a separate issue to tackle it. Thanks a…”
“Oh well 🙈 learnt some things along the way at least. Let's see when/if python/cpython#16455 is merged. Thanks for the link @pquentin.”
“It looks like asyncio is reverting the new streaming API: https://bugs.python.org/issue38242. Does that means the work from #369 is going to be irrelevant?”
“So we're going to have to support both eventually, hmm.”
Failure Signature (Search String)
- This is not a trivial API change, and I don't know if there are plans to back-port `asyncio.connect()` to 3.7 and below.
Copy-friendly signature
signature.txt
Failure Signature
-----------------
Python 3.8 builds are filled with warnings about asyncio API changes: https://travis-ci.org/encode/httpx/jobs/574559125
This is not a trivial API change, and I don't know if there are plans to back-port `asyncio.connect()` to 3.7 and below.
Error Message
Signature-only (no traceback captured)
error.txt
Error Message
-------------
Python 3.8 builds are filled with warnings about asyncio API changes: https://travis-ci.org/encode/httpx/jobs/574559125
This is not a trivial API change, and I don't know if there are plans to back-port `asyncio.connect()` to 3.7 and below.
Minimal Reproduction
repro.py
# < 3.8
reader, writer = await asyncio.open_connection('127.0.0.1', 8888)
# 3.8+
async with asyncio.connect('127.0.0.1', 8888) as stream:
...
# or:
stream = await asyncio.connect('127.0.0.1', 8888)
Environment
- Python: 3.8
What Broke
Warnings about deprecated asyncio API lead to confusion and potential runtime errors in production.
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
Upgrade to version 0.7.3 or later.
When NOT to use: This fix is not suitable for environments running Python versions below 3.7.
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/369
First fixed release: 0.7.3
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix is not suitable for environments running Python versions below 3.7.
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 |
|---|---|
| 3.8 | Broken |
| 0.7.3 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.