The new GPT-5.6 family: Luna, Terra, Sol
Simon Willison 6 days ago
OpenAI released three new GPT-5.6 models—Luna, Terra, and Sol—with input/output token prices of $1/$6, $2.50/$15, and $5/$30 respectively. On Agents' Last Exam benchmark measuring long-running professional workflows across 55 fields, GPT-5.6 Sol scored 53.6 compared to Claude Fable 5's 40.5, while Luna and Terra matched Fable 5's performance at one-sixteenth the cost. The models include new API features for programmatic tool composition, multi-agent spawning, and explicit prompt cache breakpoints, expanding capabilities for agentic workflows.