OpenAI releases GPT-5.5 and GPT-5.5 Pro in the API

Released GPT-5.5, a new frontier model for complex professional work, to the Chat Completions and Responses API, and released GPT-5.5 pro for Responses API requests for tougher problems that benefit from more compute.

GPT-5.5 supports a 1M token context window, image input, structured outputs, function calling, prompt caching, Batch, tool search, built-in computer use, hosted shell, apply patch, Skills, MCP, and web search. Key updates include:

• Reasoning effort now defaults to medium.
• When image_detail is unset or set to auto, the model now uses original behavior.
• Caching for GPT-5.5 only works with extended prompt caching. In-memory prompt caching is not supported. Learn more here.