The Fix
Upgrade to version 0.23.2 or later.
Based on closed encode/httpx issue #2491 · 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%.
@@ -114,7 +114,11 @@ def encode_content(
return headers, ByteStream(body)
- elif isinstance(content, Iterable):
+ elif isinstance(content, Iterable) and not isinstance(content, dict):
+ # `not isinstance(content, dict)` is a bit oddly specific, but it
repro.py
# Look, this error message makes sense...
>> httpx.post("https://www.example.com", content=123)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_api.py", line 304, in post
return request(
^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_api.py", line 100, in request
return client.request(
^^^^^^^^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_client.py", line 808, in request
request = self.build_request(
^^^^^^^^^^^^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_client.py", line 360, in build_request
return Request(
^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_models.py", line 339, in __init__
headers, stream = encode_request(
^^^^^^^^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_content.py", line 205, in encode_request
return encode_content(content)
^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_content.py", line 130, in encode_content
raise TypeError(f"Unexpected type for 'content', {type(content)!r}")
TypeError: Unexpected type for 'content', <class 'int'>
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 0.23.2 or later.\nWhen NOT to use: This fix is not applicable if the content type is valid and expected by the API.\n\n
Why This Fix Works in Production
- Trigger: this raises a `RuntimeError: Attempted to send an sync request with an AsyncClient instance.` (full traceback in the `<details>` below.)
- Mechanism: The content argument was incorrectly accepting a dictionary, leading to a confusing runtime error
- Why the fix works: Raises a TypeError if a dictionary is passed to the content argument, addressing the confusing error message users encounter. (first fixed release: 0.23.2).
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 3.9 in real deployments (not just unit tests).
- The content argument was incorrectly accepting a dictionary, leading to a confusing runtime error
- Surfaces as: this raises a `RuntimeError: Attempted to send an sync request with an AsyncClient instance.` (full traceback in the `<details>` below.)
Proof / Evidence
- GitHub issue: #2491
- Fix PR: https://github.com/encode/httpx/pull/2495
- First fixed release: 0.23.2
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.30
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“> I need to interact with an API that accepts DELETE requests requiring JSON content in the body”
“To improve our UX here we ought to be raising a TypeError if a dictionary is passed in the content=..”
Failure Signature (Search String)
- this raises a `RuntimeError: Attempted to send an sync request with an AsyncClient instance.` (full traceback in the `<details>` below.)
Error Message
Stack trace
error.txt
Error Message
-------------
this raises a `RuntimeError: Attempted to send an sync request with an AsyncClient instance.` (full traceback in the `<details>` below.)
Am I missing the right way for calling the `request()` method with an `AsyncClient`?
<details>
<pre>
Traceback (most recent call last):
File "*******/minimal.py", line 14, in <module>
asyncio.run(test_request_method())
File "/opt/homebrew/Cellar/[email protected]/3.9.13_3/Frameworks/Python.framework/Versions/3.9/lib/python3.9/asyncio/runners.py", line 44, in run
return loop.run_until_complete(main)
File "/opt/homebrew/Cellar/[email protected]/3.9.13_3/Frameworks/Python.framework/Versions/3.9/lib/python3.9/asyncio/base_events.py", line 647, in run_until_complete
return future.result()
File "*********minimal.py", line 11, in test_request_method
response = await ac.request(method="DELETE", url="/", content={"foo": "bar"})
File "*********/lib/python3.9/site-packages/httpx/_client.py", line 1527, in request
return await self.send(request, auth=auth, follow_redirects=follow_redirects)
File "*********/lib/python3.9/site-packages/httpx/_client.py", line 1614, in send
response = await self._send_handling_auth(
File "*********/lib/python3.9/site-packages/httpx/_client.py", line 1642, in _send_handling_auth
response = await self._send_handling_redirects(
File "*********/lib/python3.9/site-packages/httpx/_client.py", line 1
... (truncated) ...
Minimal Reproduction
repro.py
# Look, this error message makes sense...
>> httpx.post("https://www.example.com", content=123)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_api.py", line 304, in post
return request(
^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_api.py", line 100, in request
return client.request(
^^^^^^^^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_client.py", line 808, in request
request = self.build_request(
^^^^^^^^^^^^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_client.py", line 360, in build_request
return Request(
^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_models.py", line 339, in __init__
headers, stream = encode_request(
^^^^^^^^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_content.py", line 205, in encode_request
return encode_content(content)
^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/tomchristie/GitHub/encode/httpx/httpx/_content.py", line 130, in encode_content
raise TypeError(f"Unexpected type for 'content', {type(content)!r}")
TypeError: Unexpected type for 'content', <class 'int'>
Environment
- Python: 3.9
What Broke
Users encountered a runtime error when sending a DELETE request with incorrect content type.
Why It Broke
The content argument was incorrectly accepting a dictionary, leading to a confusing runtime error
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
Upgrade to version 0.23.2 or later.
When NOT to use: This fix is not applicable if the content type is valid and expected by the API.
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/2495
First fixed release: 0.23.2
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix is not applicable if the content type is valid and expected by the API.
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 |
|---|---|
| 0.23.2 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.