OpenAI launches GPT-5.6, brings Codex to ChatGPT

GPT-5.6 introduces Sol and Terra models, with Luna outperforming GPT-5.5 at 25x lower cost. Codex is now integrated into ChatGPT, gaining features like parallel work, inline edits, and sites. OpenAI reports 7M+ weekly Codex users and 150+ updates in two months.