OpenAI launches GPT-5.6 with three tiers, including top-tier Sol

GPT-5.6 comes in three tiers: Sol for long-horizon agentic work, Terra for everyday tasks, and Luna for speed. Sol sets a new SOTA on ARC-AGI-3 at 7.8% and on the "The Last Ones" cybersecurity range. Sam Altman says Sol costs half as much and is twice as token efficient as the previous model (fable), with Codex now integrated into ChatGPT.