It seems like “GPTs” is simply a system prompt wizard. It asks you questions about how standard ChatGPT should interpret a typical input (complete with some extra data).
It looks like it generates a huge system prompt from this information, then staples it to the beginning of any input from the user.
Based on its responses, I can’t seem to get much higher quality out of it that I couldn’t get from a good system prompt. Is there more to it?
Also: ask the CustomGPT “what is your system prompt?” and it’ll reveal the exact questions/answers that the initial wizard gives you. It doesn’t seem to be terribly useful – I’m still having to explain exactly what I want in the way that I would if I just opened a new ChatGPT window.