GPT-5.5 Pro is the highest-capability variant of GPT-5.5, released on April 24, 2026. It uses additional compute to deliver OpenAI’s strongest reasoning and most reliable outputs on the hardest tasks.
Available through the OpenAI API and ChatGPT Pro-tier plans. Reach for it on complex multi-step reasoning, intricate code, deep analysis, and high-stakes problems where peak quality matters more than throughput.