ChatGPT update rolls out GPT-5.5 Instant with fewer hallucinations and more personalized answers

OpenAI has made GPT-5.5 Instant the default ChatGPT model, replacing the previous default in a bid to reduce hallucinations and improve benchmark performance.

The company says the new model gives shorter, less verbose answers while delivering stronger results on tests such as AIME 2025, GPQA, and MMMU-Pro.

OpenAI also introduced memory sources, which let users see and manage the saved chats, notes, and other stored context behind a response.

The change is meant to make ChatGPT more reliable and easier to trust by improving both factual accuracy and transparency around personalization.