OpenAI has updated ChatGPT’s default model to GPT-5.5 Instant, replacing GPT-5.3 Instant for all users. The update delivers stronger factual accuracy, more concise responses and improved personalization by making better use of context users have already shared across conversations.
In 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. It also reduced inaccurate claims by 37.3% on conversations flagged for factual errors, with additional gains in visual reasoning, math and science benchmarks.
The model delivers tighter, more direct responses without sacrificing substance, while reducing verbosity, overformatting and unnecessary follow-up questions. OpenAI is also introducing memory sources across all ChatGPT models, giving users visibility into what context was used to personalize responses, with controls to delete or correct outdated information.
Enhanced personalization from past chats, files and connected Gmail is rolling out to Plus and Pro users on the web, with plans to expand to Free, Go, Business and Enterprise users in coming weeks. For paid users, GPT-5.3 Instant will remain available for three months through model configuration settings before being retired.
KEY QUOTE:
“GPT-5.5 Instant uses 30.2% fewer words and 29.2% fewer lines. Its response is stronger because it gets the tone right: informal, practical, and workplace-safe without overexplaining.”
OpenAI, Internal Evaluation Summary
