The Fix
Prevent errors when using aiohttp from a Python 3.14 build that does not include compression.zstd support.
Based on closed aio-libs/aiohttp issue #11603 · 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 @@
@@ -0,0 +1 @@
+Fixed Python 3.14 support when built without ``zstd`` support -- by :user:`JacobHenner`.
diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index f123d1543fe..b64d99fb632 100644
repro.py
import aiohttp
.tox/test/lib/python3.14/site-packages/aiohttp/__init__.py:6: in <module>
from .client import (
.tox/test/lib/python3.14/site-packages/aiohttp/client.py:40: in <module>
from . import hdrs, http, payload
.tox/test/lib/python3.14/site-packages/aiohttp/http.py:7: in <module>
from .http_parser import (
.tox/test/lib/python3.14/site-packages/aiohttp/http_parser.py:29: in <module>
from .compression_utils import (
.tox/test/lib/python3.14/site-packages/aiohttp/compression_utils.py:25: in <module>
import compression.zstd # noqa: I900
^^^^^^^^^^^^^^^^^^^^^^^
/opt/python/3.14/lib/python3.14/compression/zstd/__init__.py:29: in <module>
import _zstd
E ModuleNotFoundError: No module named '_zstd'
verify
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
fix.md
Option A — Apply the official fix\nPrevent errors when using aiohttp from a Python 3.14 build that does not include compression.zstd support.\nWhen NOT to use: This fix should not be used if zstd support is required for functionality.\n\n
Why This Fix Works in Production
- Trigger: import aiohttp
- Mechanism: Prevent errors when using aiohttp from a Python 3.14 build that does not include compression.zstd support.
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
- Shows up under Python 3.14 in real deployments (not just unit tests).
- Surfaces as: import aiohttp
Proof / Evidence
- GitHub issue: #11603
- Fix PR: https://github.com/aio-libs/aiohttp/pull/11611
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.70
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.33
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Related to https://github.com/python/cpython/issues/139707”
“Yeah, we can probably work around that, similar to the <3.14 approach.”
Failure Signature (Search String)
- import aiohttp
Error Message
Stack trace
error.txt
Error Message
-------------
import aiohttp
.tox/test/lib/python3.14/site-packages/aiohttp/__init__.py:6: in <module>
from .client import (
.tox/test/lib/python3.14/site-packages/aiohttp/client.py:40: in <module>
from . import hdrs, http, payload
.tox/test/lib/python3.14/site-packages/aiohttp/http.py:7: in <module>
from .http_parser import (
.tox/test/lib/python3.14/site-packages/aiohttp/http_parser.py:29: in <module>
from .compression_utils import (
.tox/test/lib/python3.14/site-packages/aiohttp/compression_utils.py:25: in <module>
import compression.zstd # noqa: I900
^^^^^^^^^^^^^^^^^^^^^^^
/opt/python/3.14/lib/python3.14/compression/zstd/__init__.py:29: in <module>
import _zstd
E ModuleNotFoundError: No module named '_zstd'
Minimal Reproduction
repro.py
import aiohttp
.tox/test/lib/python3.14/site-packages/aiohttp/__init__.py:6: in <module>
from .client import (
.tox/test/lib/python3.14/site-packages/aiohttp/client.py:40: in <module>
from . import hdrs, http, payload
.tox/test/lib/python3.14/site-packages/aiohttp/http.py:7: in <module>
from .http_parser import (
.tox/test/lib/python3.14/site-packages/aiohttp/http_parser.py:29: in <module>
from .compression_utils import (
.tox/test/lib/python3.14/site-packages/aiohttp/compression_utils.py:25: in <module>
import compression.zstd # noqa: I900
^^^^^^^^^^^^^^^^^^^^^^^
/opt/python/3.14/lib/python3.14/compression/zstd/__init__.py:29: in <module>
import _zstd
E ModuleNotFoundError: No module named '_zstd'
Environment
- Python: 3.14
Fix Options (Details)
Option A — Apply the official fix
Prevent errors when using aiohttp from a Python 3.14 build that does not include compression.zstd support.
When NOT to use: This fix should not be used if zstd support is required for functionality.
Fix reference: https://github.com/aio-libs/aiohttp/pull/11611
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix should not be used if zstd support is required for functionality.
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
- Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
- Pin production dependencies and upgrade only with a reproducible test that hits the failing path.
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.