TypeError object of type 'Omit' has no len()

[browniebroke]

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Describe the bug

After upgrading from openai-agents from 0.1.0 to 0.4.1, we got this error in production. We didn't observe this error on our staging or development environments and even after the fact we're unable to reproduce.

This happens when calling await Runner.run(agent, ...) and the stack trace points to this line:

openai-agents-python/src/agents/models/openai_chatcompletions.py

Line 293 in 1466ddb

ret = await self._get_client().chat.completions.create(

So my best guess is that it's somewhat related to:

• Migrate openai from 1.x to 2.2.0 #1874

As the NotGiven was changed to Omit but several arguments were changed, so it's a bit tricky to track which one causes an issue.

Debug information

• Agents SDK version: 0.4.1
• OpenAI version: 2.6.0
• Python version 3.13.9

Repro steps

I can't reproduce outside of our production environment yet, but I'm still investigating. We also use Datadog for observability (ddtrace 3.16.1), and it's typically not installed in the dev environment, so I'm suspecting that it might patch something in a weird way causing that.

Has anyone else encountered this error?

Expected behavior

No error when calling the runner.