GPT-5 in ChatGPT is our next flagship model and the new default for all logged-in users. It simplifies ChatGPT to a single auto-switching system that brings together the best of our previous models into a smart, fast model. Breakthrough reasoning is built in: GPT-5 can “think” more deeply when a problem benefits from careful analysis, especially for complex work like coding, science …
https://help.openai.com/en/articles/11909943-gpt-5-in-chatgpt