OpenAI's new GPT-5.5 Instant default model shows 52.5% fewer hallucinated claims on high-stakes prompts, the company says

OpenAI is rolling out GPT-5.5 Instant as ChatGPT's new default model starting Tuesday to all ChatGPT users. GPT-5.3 Instant will remain available as an option for three months before being retired.

Based on internal evaluations, GPT-5.5 Instant produced "52.5% fewer hallucinated claims" than GPT-5.3 Instant on high-stakes prompts covering medicine, law, and finance, and "reduced inaccurate claims by 37.3%" on especially challenging conversations users had flagged for factual errors. The model also offers tighter responses and improved ability to pull context from previous chats and Gmail for more personalized answers.

A new "memory sources" feature rolling out now on the web (and soon on mobile) lets ChatGPT show what context was used to inform personalized responses, and users can delete or correct information. Enhanced personalization is rolling out first to Plus and Pro users on the web and is coming soon to mobile apps and Free, Go, Business, and Enterprise plans.