GPT-5
OpenAI brought its two lines into one model with a router that decides for itself when to answer at once and when to think longer.
Why it matters
The choice of model was taken away from the user, and that turned out to be a more visible change than any gain in quality.
Until then the list held eight options and a user had to know which was for what. Here there is one entry and a router inside. Technically it is tidying up; in practice the release was contentious. The router worked badly in the first days, and the attachment of some users to the previous model proved strong enough that the company restored its availability. The episode showed what no measurement had: for many people the model had become not a tool to be replaced but an interlocutor they recognised.