OpenAI Ships GPT-5.6 Family (Sol/Terra/Luna) to API and Codex, Claims +13.1 on Agents' Last Exam vs Claude Fable 5

OpenAI·high signal

OpenAI launched the GPT-5.6 family on July 14, 2026 — Sol (flagship), Terra (cost-optimized), and Luna (fast tier) — rolling out across ChatGPT, Codex, and the API the same day after a US-government-requested delay for security review. GPT-5.6 Sol scored 53.6 on Agents' Last Exam, beating Claude Fable 5 (adaptive reasoning) by 13.1 points; at medium reasoning it exceeded Fable 5 by 11.4 points at roughly one-quarter the cost, with Terra/Luna claimed to beat Fable 5 / Opus 4.8 at ~1/5 the API cost. Sol adds an 'Ultra' subagent mode and a 'Max' reasoning-effort setting.