Summary
OpenAI updated ChatGPT's default model to GPT-5.5 Instant and also exposed it in the API as chat-latest. The company says the release improves factuality, shortens responses, and expands personalization through past chats, files, and connected Gmail where available.
What changed
OpenAI replaced GPT-5.3 Instant with GPT-5.5 Instant as the default ChatGPT model and started rolling out new memory-source and personalization behavior alongside it.
Why it matters
Default-model changes matter more than niche model launches because they reset the baseline experience for a very large installed base. This also shows OpenAI combining quality gains with deeper memory-driven personalization, which puts pressure on competing assistants to improve context reuse without making the product feel heavier.
Evidence excerpt
OpenAI says GPT-5.5 Instant is replacing GPT-5.3 Instant as ChatGPT's default and is also available through chat-latest in the API.