GPT-5.5 Instant Becomes the Default ChatGPT Model for All Users, Replacing GPT-5.3 Instant

OpenAI·medium signal

OpenAI began rolling out GPT-5.5 Instant on June 9 as the new default across all ChatGPT tiers, including Go and Free, retiring GPT-5.3 Instant. It targets factual reliability, tighter answers, better image understanding and STEM, and smarter decisions about when to search the web. For builders, the default-model swap means consumer-facing prompt behavior shifts without any opt-in.