OpenAI releases GPT-5.5 Instant, a new default model for ChatGPT

On Tuesday, OpenAI released GPT-5.5 Instant, a new foundation model that becomes the default model for ChatGPT, replacing GPT-5.3 Instant. The company emphasizes reduced hallucinations in sensitive domains such as law, medicine, and finance, while keeping the same low latency as its predecessor. On benchmarks, GPT-5.5 Instant achieved a score of 81.2 on the AIME 2025 math test (up from 65.4) and 76 on the MMMU-Pro multimodal reasoning benchmark (up from 69.2), demonstrating significant improvements in mathematical and multimodal reasoning.

The release introduces enhanced context management: GPT-5.5 Instant can use its search tool to refer back to past conversations, uploaded files, and Gmail to deliver more personalized answers. This feature is rolling out first to Plus and Pro users on the web, with mobile access planned soon, and Free, Go Business, and enterprise users gaining access in the coming weeks. ChatGPT will now also show memory sources across all models, allowing users to delete or correct outdated information. Crucially, when sharing a chat, memory sources are not visible to others. For developers, GPT-5.5 is available via API as "chat-latest", while GPT-5.3 remains accessible for paid users for only three months—a cautious move after backlash from the GPT-4o deprecation, which users had petitioned to keep.