OpenAI updates ChatGPT's default model to GPT-5.5 Instant with improved factuality, reasoning, and personalization

GPT-5.5 Instant is rolling out starting today to all ChatGPT users as the new default model, replacing GPT-5.3 Instant. For paid users, GPT-5.3 Instant will remain available for three months before being retired.

In internal evaluations, GPT-5.5 Instant produced 52.5% fewer hallucinated claims than GPT-5.3 Instant on high-stakes prompts in medicine, law, and finance, and reduced inaccurate claims by 37.3% on especially challenging conversations flagged for factual errors.

The model delivers tighter, more concise responses while improving at using context from past chats, files, and connected Gmail. Memory sources—a new feature showing what context was used to personalize responses—are rolling out across all ChatGPT consumer plans on the web and soon on mobile, with controls to delete or correct outdated information.