I'm not seeing anything there that can't be done with the basic API with tool use added - ie. you call the API, sending the users query and information and examples of available tools. The API responds saying it wishes to use a tool, and which tool it wants to use. You then do whatever the tool does (eg. some math). You then call the API again, with the previous state, plus the result of the calculations, and GPT-4 then responds with the reply to the user.