[Responses API] Support tool calling and ouput token streaming

[markmc]

Splitting off from #14721

FYI a start has been made here #20504

That PR (which was merged to main on 7/9/2025) explicitly has an unchecked boxes for

• Tool/functional calling support
• Output token streaming

Any plans to implement those features? I think that is what is needed to support agentic coding tools like codex. See:

• https://docs.vllm.ai/projects/recipes/en/latest/OpenAI/GPT-OSS.html#harmony-format-support

Originally posted by @bartlettroscoe in #14721

[bartlettroscoe]

Do we know anyone who might be able to work on this and when? Just curious.

NOTE: For now, we are getting by with llama-swap/llama.cpp to serve the gpt-oss models for usage with local Codex CLI. But that is not a very scalable solution.

[cjackal]

Do we know anyone who might be able to work on this and when? Just curious.

NOTE: For now, we are getting by with llama-swap/llama.cpp to serve the gpt-oss models for usage with local Codex CLI. But that is not a very scalable solution.

#26874 covers the tool calling part of the issue.

[bartlettroscoe]

With the merge of:

• [Frontend] OpenAI Responses API supports Tool/Function calling - non-harmony  #26874

Is this now complete?