[Bug] Bug report: Model switching mid conversation

mid conversation I switched from gpt-5-nano to gpt-5.6-sol and got the following error:

Unknown Error "litellm.BadRequestError: OpenAIException - Function tools with reasoning_effort are not supported for gpt-5.6-sol in /v1/chat/completions. To use function tools, use /v1/responses or set reasoning_eff | provider=openai | model=gpt-5.6-sol | upstream_status=400"

not a major issue for me, but I wanted to let you know.

Start by reproducing the mid-conversation switch from gpt-5-nano to gpt-5.6-sol and trace the request path that produces the reported LiteLLM.BadRequestError. Determine whether the model switch can complete without the function-tools and reasoning_effort error, then verify the same conversation flow works.

Written by the indexing model from the issue text.