ChatCompletionMessageToolCallParam "cannot instantiate typing.Union" error in 1.99.4

[tylerpayne]

Confirm this is an issue with the Python library and not an underlying OpenAI API

• This is an issue with the Python library

Describe the bug

Release 1.99.4 fixed a regression where ChatCompletionToolParam had changed from a TypedDict to a Union, causing any existing ChatCompletionToolParam(...) constructors to break.

The same error is still occurring when trying to instantiate ChatCompletionMessageToolCallParam.

Python 3.12.10 (main, May 30 2025, 05:53:56) [Clang 20.1.4 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import openai
>>> openai.__version__
'1.99.4'
>>> from openai.types.chat import ChatCompletionMessageToolCallParam
>>> ChatCompletionMessageToolCallParam()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/tylerpayne/.local/share/uv/python/cpython-3.12.10-macos-aarch64-none/lib/python3.12/typing.py", line 1184, in __call__
    result = self.__origin__(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/tylerpayne/.local/share/uv/python/cpython-3.12.10-macos-aarch64-none/lib/python3.12/typing.py", line 501, in __call__
    raise TypeError(f"Cannot instantiate {self!r}")
TypeError: Cannot instantiate typing.Union

To Reproduce

uvx --python 3.12 --with "openai==1.99.4" python

from openai.types.chat import ChatCompletionMessageToolCallParam
ChatCompletionMessageToolCallParam()

Code snippets

OS

macOS

Python version

Python v3.12.10

Library version

openai v1.99.4

[bprh]

Present for me in 1.99.3

[wriga049]

And 1.99.5

[pyth0nic]

Still a problem in 1.99.5

[ultmaster]

Still a problem with 1.99.6

________ test_run_with_agentops_tracer[openai_agents_sdk_mcp_tool_use] _________

agent_func = <function openai_agents_sdk_mcp_tool_use at 0x7fc6d798a020>

    @pytest.mark.parametrize("agent_func", list(iterate_over_agents()), ids=lambda f: f.__name__)
    def test_run_with_agentops_tracer(agent_func):
        tracer = AgentOpsTracer()
        tracer.init()
        tracer.init_worker(0)
    
        global _langchain_callback_handler
        _langchain_callback_handler = tracer.get_langchain_callback_handler()
    
        try:
>           tracer.trace_run(
                run_one,
                agent_func,
            )

tests/test_tracer.py:803: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
agentlightning/tracer/base.py:80: in trace_run
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
tests/test_tracer.py:675: in run_one
    asyncio.get_event_loop().run_until_complete(run_agent(agent_func))
uvloop/loop.pyx:1518: in uvloop.loop.Loop.run_until_complete
    ???
tests/test_tracer.py:216: in run_agent
    return await agent_func()
           ^^^^^^^^^^^^^^^^^^
tests/test_tracer.py:494: in openai_agents_sdk_mcp_tool_use
    result = await Runner.run(agent, "What is 43*57?", run_config=openai_agents_sdk_run_config())
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/site-packages/agents/run.py:206: in run
    return await runner.run(
/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/site-packages/agents/run.py:434: in run
    turn_result = await self._run_single_turn(
/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/site-packages/agents/run.py:956: in _run_single_turn
    new_response = await cls._get_new_response(
/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/site-packages/agents/run.py:1168: in _get_new_response
    new_response = await model.get_response(
/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/site-packages/agents/models/openai_chatcompletions.py:66: in get_response
    response = await self._fetch_response(
/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/site-packages/agents/models/openai_chatcompletions.py:228: in _fetch_response
    converted_messages = Converter.items_to_messages(input)
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/site-packages/agents/models/chatcmpl_converter.py:443: in items_to_messages
    new_tool_call = ChatCompletionMessageToolCallParam(
/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/typing.py:1184: in __call__
    result = self.__origin__(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = typing.Union, args = ()
kwds = {'function': {'arguments': '{"expression":"43*57"}', 'name': 'calculate'}, 'id': 'call_AiUOswhpHBBfEjapoaC5iOe3', 'type': 'function'}

    def __call__(self, *args, **kwds):
>       raise TypeError(f"Cannot instantiate {self!r}")
E       TypeError: Cannot instantiate typing.Union

[ryx2]

Hey we're really feeling the pain of this bug over here and tracking it through this issue for pydantic ai as well: pydantic/pydantic-ai#2476

[ryx2]

just made the PR #2543 to fix, who do i need to bug to get this merged i wonder

[RobertCraigie]

Thanks for the report and sorry for the regression, this will be fixed in the next release #2551.

[RobertCraigie]

This has been fixed in 1.99.7