They sure make this hard to figure out. On https://openai.com/product/gpt-4 it says "GPT-4 is OpenAI’s most advanced system, producing safer and more useful responses" and below it two links: "Try on ChatGPT Plus" and "Join API waitlist". The first link takes me to ChatGPT Mar23 version. You're saying that that's not GPT-4?
It's also disturbing the way they are using the term "Safety & alignment". It's as if they are trying to steer what that means in the direction of DEI or NSFW and away from existential risk.
Correct, that is Legacy (GPT 3.5). On a paying account, when you start a conversation there is a dropdown where you can select which model to use. The choices are Default (GPT-3.5) optimized for speed, Legacy (GPT-3.5), GPT-4.
alternatively, you can sign up/request for api access here - https://openai.com/waitlist/gpt-4-api