OpenAI's unreleased flagship model GPT-5.6, codenamed iris-alpha, was discovered in backend logs. Its key breakthrough is a record 1.5 million token context window, a 43% increase over GPT-5.5, enabling it to process long documents and complex tasks. The model also demonstrated advanced frontend generation, creating a functional app interface called Lumen Notes without detailed prompts. An official release is expected in June.