PRODUCTION SCENARIO
Northgate's wrapper builds one request body and sends it to both Chat Completions and the Responses API. The Responses API calls return a 400 naming an unsupported parameter; the identical fields are accepted on Chat Completions.
What is the appropriate repair?
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Answer: Map reasoning_effort to reasoning.effort on the requests that target the Responses API
Reasoning effort is reasoning.effort on the Responses API and reasoning_effort on Chat Completions, so a shared body has to be mapped per endpoint rather than sent unchanged. Sending both fails on whichever endpoint does not recognise one of them, stripping the rejected field silently drops the effort setting the integration configured, and there is no dated API version to pin that restores the older names.
Official Source: https://developers.openai.com/api/docs/guides/reasoning ↗