Model Overview
GPT-5.5 is OpenAI's most capable model as of April 2026. It processes text, images, audio, and video in a single unified architecture — unlike previous multimodal models that stitched separate models together. It excels at agentic coding, computer use, knowledge work, and scientific research. The model supports a 1M token context window in the API and 400K in Codex. It was co-designed with NVIDIA GB200/GB300 hardware and used Codex to rewrite its own serving infrastructure before launch, improving token generation speeds by over 20%.