OpenAI launches GPT-5.5 Instant as ChatGPT default

OpenAI debuted GPT-5.5 Instant May 5 as ChatGPT's baseline model, with search over prior conversations, file attachments, and Gmail integration for personalized responses. It scores 81.2 on AIME 2025 math and 76 on MMMU-Pro multimodal (up from 69.2). Available to Plus and Pro users first.