I don’t know about Gab specifically, but yes, in general you can do that. OpenAI makes their base model available to developers via API. All of these chatbots, including the official ChatGPT instance you can use on OpenAI’s web site, have what’s called a “system prompt”. This includes directives and information that are not part of the foundational model. In most cases, the companies try to hide the system prompts from users, viewing it as a kind of “secret sauce”. In most cases, the chatbots can be made to reveal the system prompt anyway.

Anyone can plug into OpenAI’s API and make their own chatbot. I’m not sure what kind of guardrails OpenAI puts on the API, but so far U don’t think there are any techniques that are very effective in preventing misuse.

I can’t tell you if that’s the ONLY thing that differentiates ChatGPT from this. ChatGPT is closed-source so they could be doing using an entirely different model behind the scenes. But it’s similar, at least.