builtins.RuntimeError: <asyncio.locks.Event object at 0xffff3743a090 [unset]> is bound to a different event loop.

[ruidc]

Initial Checks

• I confirm that I'm using the latest version of Pydantic AI
• I confirm that I searched for my issue in https://github.com/pydantic/pydantic-ai/issues before opening this issue

Description

After upgrading from 1.1.0 to 1.4.0 without any code changes, I am now getting the following error:

Traceback (most recent call last):
  File "/usr/local/lib/python3.13/site-packages/google/genai/_api_client.py", line 1293, in _async_request
    return await self._async_retry(  # type: ignore[no-any-return]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        self._async_request_once, http_request, stream
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/tenacity/asyncio/__init__.py", line 111, in __call__
    do = await self.iter(retry_state=retry_state)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/tenacity/asyncio/__init__.py", line 153, in iter
    result = await action(retry_state)
             ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/tenacity/_utils.py", line 99, in inner
    return call(*args, **kwargs)
  File "/usr/local/lib/python3.13/site-packages/tenacity/__init__.py", line 420, in exc_check
    raise retry_exc.reraise()
          ~~~~~~~~~~~~~~~~~^^
  File "/usr/local/lib/python3.13/site-packages/tenacity/__init__.py", line 187, in reraise
    raise self.last_attempt.result()
          ~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/usr/local/lib/python3.13/concurrent/futures/_base.py", line 449, in result
    return self.__get_result()
           ~~~~~~~~~~~~~~~~~^^
  File "/usr/local/lib/python3.13/concurrent/futures/_base.py", line 401, in __get_result
    raise self._exception
  File "/usr/local/lib/python3.13/site-packages/tenacity/asyncio/__init__.py", line 114, in __call__
    result = await fn(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/google/genai/_api_client.py", line 1266, in _async_request_once
    client_response = await self._async_httpx_client.request(
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<5 lines>...
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/httpx/_client.py", line 1540, in request
    return await self.send(request, auth=auth, follow_redirects=follow_redirects)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/ddtrace/contrib/internal/httpx/patch.py", line 138, in _wrapped_async_send
    resp = await wrapped(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/httpx/_client.py", line 1629, in send
    response = await self._send_handling_auth(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<4 lines>...
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/httpx/_client.py", line 1657, in _send_handling_auth
    response = await self._send_handling_redirects(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<3 lines>...
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/httpx/_client.py", line 1694, in _send_handling_redirects
    response = await self._send_single_request(request)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/httpx/_client.py", line 1730, in _send_single_request
    response = await transport.handle_async_request(request)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/httpx/_transports/default.py", line 394, in handle_async_request
    resp = await self._pool.handle_async_request(req)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/httpcore/_async/connection_pool.py", line 256, in handle_async_request
    raise exc from None
  File "/usr/local/lib/python3.13/site-packages/httpcore/_async/connection_pool.py", line 236, in handle_async_request
    response = await connection.handle_async_request(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        pool_request.request
        ^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/httpcore/_async/connection.py", line 103, in handle_async_request
    return await self._connection.handle_async_request(request)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/httpcore/_async/http11.py", line 136, in handle_async_request
    raise exc
  File "/usr/local/lib/python3.13/site-packages/httpcore/_async/http11.py", line 106, in handle_async_request
    ) = await self._receive_response_headers(**kwargs)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/httpcore/_async/http11.py", line 177, in _receive_response_headers
    event = await self._receive_event(timeout=timeout)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/httpcore/_async/http11.py", line 217, in _receive_event
    data = await self._network_stream.read(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        self.READ_NUM_BYTES, timeout=timeout
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/httpcore/_backends/anyio.py", line 35, in read
    return await self._stream.receive(max_bytes=max_bytes)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/anyio/streams/tls.py", line 237, in receive
    data = await self._call_sslobject_method(self._ssl_object.read, max_bytes)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/anyio/streams/tls.py", line 180, in _call_sslobject_method
    data = await self.transport_stream.receive()
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/anyio/_backends/_asyncio.py", line 1263, in receive
    await self._protocol.read_event.wait()
  File "/usr/local/lib/python3.13/asyncio/locks.py", line 210, in wait
    fut = self._get_loop().create_future()
          ~~~~~~~~~~~~~~^^
  File "/usr/local/lib/python3.13/asyncio/mixins.py", line 20, in _get_loop
    raise RuntimeError(f'{self!r} is bound to a different event loop')
RuntimeError: <asyncio.locks.Event object at 0xffff401736b0 [unset]> is bound to a different event loop

Example Code

If required, I'll endeavour to create a minimal example and bisect, as many of the below packages were updated to latest at the same time.

Python, Pydantic AI & LLM client version

Stack is (all latest):

fastapi==0.120.0
pydantic==2.12.3
uvicorn[standard]==0.38.0
#for database   #new
sqlalchemy==2.0.44
psycopg[binary,pool]==3.2.10
#for loading environment variables
python-dotenv==1.1.1
requests==2.32.5
# Specific version required by fastapi
starlette==0.48.0
Pillow==12.0.0
boto3==1.40.58
botocore==1.40.58
ddtrace==3.17.0
aiohttp==3.13.0
aiolimiter==1.2.1
JSON-log-formatter==1.1.1
pydantic-ai-slim[google,openai]==1.4.0

using gemini-2.5-flash-lite

[DouweM]

@ruidc Thanks for the report. I expect this is caused by #3217 which bumps google-genai to get googleapis/python-genai#1509 and now passes in our own httpx.AsyncClient.

I'm not sure how you're ending up with 2 event loops though, with self._protocol.read_event having been created in a different one than where await self._protocol.read_event.wait() is eventually called. A minimal reproducible example would be very helpful.

[ruidc]

Thanks, as the error appeared to be intermittent, I only observed it on production and needed to rollback the version quickly, I didn't get time to analyze further, but I'll see if I can produce a minimal example.

[DouweM]

@ruidc Thanks, I realize it'll be hard to catch this again without bothering users...

Just to rule some things out, you're not intentionally/explicitly managing different event loops?

[ruidc]

No not at all, using very vanilla code lifted from the docs.

[DouweM]

@ruidc Hmm, and you haven't seen it in testing, only in prod?

[ruidc]

Correct, but I'll hope to have some time after the coming days when the peak retail period is over