OpenAI launches GPT 5.6 Sol/Terra/Luna, Codex becomes ChatGPT superapp

GPT-5.6 comes in three sizes (Sol, Terra, Luna) with a new 'ultra' effort level coordinating four agents. It outperforms Claude Opus 4.8 and Fable 5 at one-third the time, half the output tokens, and one-quarter the cost. Sets state-of-the-art on Terminal-Bench 2.1 and DeepSWE.