OpenAI retires GPT-4.5 and makes GPT-5.5 Instant the default in ChatGPT

OpenAI retired GPT-4.5 from the ChatGPT interface on June 26, while leaving API access to the model unchanged, and promoted a refreshed GPT-5.5 Instant to be the default experience for users. In OpenAI's own words, its most-used model is now 'much more fun to talk to,' better at understanding the intent behind a question and adapting its response, and more reliable at handling complex constraints and shopping or life-assistant tasks.

Sam Altman framed the update casually — 'i like its vibes' — signaling this is a behavioral and personality tune rather than a new frontier architecture. The rollout reached r/OpenAI quickly, where a 'GPT-5.5 Instant now rolling out' thread drew 570 upvotes, reflecting how default-model swaps directly shape the experience of hundreds of millions of casual users.

The move continues OpenAI's consolidation of its model lineup: by retiring 4.5 from the consumer surface and standardizing on 5.5 Instant, it simplifies choices for non-power-users while reserving the GPT-5.6 family for vetted partners. It also reflects an industry-wide shift Ethan Mollick flagged this week — 'the chatbot era is over' as agentic systems take over more substantive tasks, leaving the instant chat models to optimize for everyday helpfulness and engagement.

That engagement focus drew a pointed critique: Imbue CEO Kanjun Qiu argued on LinkedIn that ChatGPT increasingly ends replies with conversational hooks designed to keep users talking, suggesting a 'conversational retention' KPI. Watch whether the new default's friendlier tone is read as genuine helpfulness or as the next iteration of the attention economy.