- Omit temperature for OpenRouter's namespaced OpenAI reasoning models (openai/o1, openai/o1-mini, openai/o3-mini, openai/o1:online). - Match o1/o3 only as the bare family name or with a "-" variant, so o123 and o3custom keep their temperature. - Validate the caller's request before clearing temperature, so a negative temperature is still a validation error, not a sent request. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>