GPT-5.6 Sol

GPT-5.6, announced June 26, 2026 and generally available July 9, 2026, restructured OpenAI's lineup into three persistent capability tiers named for celestial bodies: Sol, Terra, and Luna. Sol is the flagship, built for the hardest problems in coding, cybersecurity, and multi-step agentic workflows, with max reasoning effort and an ultra mode that uses subagents. Terra matches GPT-5.5-class quality at roughly half the cost for everyday work, while Luna is the fast, cheap tier for high-volume routine tasks.

The rollout was unusual: after a US government request, OpenAI started with a limited preview for about 20 trusted partners before going public. Sol is priced at $4 per million input tokens and $20 per million output tokens after price cuts, with all three tiers sharing a 1,050,000-token context window. The bare gpt-5.6 API alias routes to Sol by default. Sol set new state-of-the-art scores on Terminal-Bench 2.1 and improved long-horizon security tasks.