It's not the same. I don't know the technical differences, but in my tests it often returns wildly different results. anecdotally the API has also hallucinated modules that don't exist (but that I wish did!) whereas the chat gpt proper has not done that to me.
> If so it might be way cheaper to use the API than ChatGPT plus?
I haven't used ChatGPT Plus, just the normal one. But at least the demonstration GIF makes it seem kind of slow. One selling point of the Plus service is supposedly that you get faster responses.
I just tested the API, it seems to have the same speed as ChatGPT plus. I quickly tested some questions and it seems that OpenAI web app has a bit more relevant answers, I wonder whether it's related to the temperature and other parameters.