Update, July 10, 2026: GPT-5.5 has since been succeeded by GPT-5.6, which reached general availability on July 9, 2026 with the Sol, Terra, and Luna tiers and is now OpenAI’s frontier model. This guide remains the deep reference on GPT-5.5, which stays available as the fast Instant default across ChatGPT tiers. On April 23, 2026, OpenAI introduced GPT-5.5, its most capable model at launch and the first fully retrained base model since GPT-4.5. The release brings state-of-the-art scores on Terminal-Bench 2.0, OSWorld, and GDPval, a much stronger agentic coding profile in Codex, a new Pro tier, and a pricing step up that reflects the jump in intelligence. GPT-5.5 is rolling […]