Summary
OpenAI introduced GPT-5.5 Instant on May 5 and began rolling it out as the default ChatGPT model, replacing GPT-5.3 Instant. The release emphasizes clearer answers, stronger personalization, and immediate availability across ChatGPT and the API.
What changed
OpenAI launched GPT-5.5 Instant, started rolling it out to all ChatGPT users as the default model, and exposed it in the API as chat-latest.
Why it matters
OpenAI is further segmenting the GPT-5 family around faster default surfaces instead of treating one frontier model as the single ChatGPT experience. That matters for teams balancing cost, speed, and model behavior across consumer and agent workflows.
Evidence excerpt
OpenAI says GPT-5.5 Instant is rolling out starting today to all ChatGPT users, replacing GPT-5.3 Instant as the default model, and is also available in the API as chat-latest.