OpenAI releases GPT-5.6 family: Luna, Terra, Sol

Jul 10, 2026

OpenAI's GPT-5.6 models are now generally available in three sizes: Luna, Terra, and Sol. They feature a 1 million token context window, 128,000 output tokens, and claim superior agentic performance on Agents' Last Exam, with Sol scoring 53.6, beating Claude Fable 5 by 13.1 points. However, on SWE-Bench Pro, Sol scored 64.6% compared to Fable 5's 80%, and OpenAI has criticized that benchmark as having approximately 30% broken tasks.

Why it matters: The GPT-5.6 family introduces tiered pricing and efficiency claims that could reshape competition in the AI model market, especially for long-running agentic tasks.

Full story at: Simon Willison's Weblog ↗