OpenAI GPT-5.6 Sol is the flagship of the GPT-5.6 family — a frontier model for complex professional work, with a 1,050,000-token context window and up to 128,000 tokens of output. Strongest reasoning, coding, multimodal understanding, and long-form writing in the family. Supports text and image input, web search, and reasoning effort / summary display options. Best for large codebases, professional reports, and deep reasoning; for everyday tasks Terra or Luna is cheaper.