GPT-5.5 Instant is starting to roll out in ChatGPT.

OpenAI is rolling out GPT-5.5 Instant to all ChatGPT users as the new default model, replacing GPT-5.3 Instant . The model produces 52.5% fewer hallucinated claims than its predecessor on high-stakes prompts in areas like medicine, law, and finance . The rollout includes a new "memory sources" feature across all ChatGPT models that shows users what context was used to personalize responses .

Source: r/ChatGPT | 2026-05-05