GPT5_5Pro
GPT-5.5 pro uses more compute to think harder and provide consistently better answers. OpenAI's model page text says GPT-5.5 pro is for Responses API requests, while the endpoint table on the same page also lists chat completions. Koog follows the textual model description and treats GPT-5.5 pro as Responses-only.
1,050,000 context window 128,000 max output tokens Dec 01, 2025 knowledge cutoff Reasoning token support