The ChatGPT Plus UI includes a model selection menu. Here is what the UI looks like when you sign in:
1. (Default) GPT-3.5
GPT-3.5 is our fastest model, which is great for most everyday tasks. This model is available to Free and Plus users.
2. GPT-4 (available to Plus users only)
GPT-4 is our most capable model, which is great for tasks that require creativity and advanced reasoning. This model is available exclusively to Plus users.
Check out our ChatGPT — Release Notes for the latest updates on ChatGPT.