[int_19h]

I think the API is meant to be the data model in this scenario. The point is that you design the API around the task that it solves, rather than against whatever fixed spec OpenAI publishes. And then you tell ChatGPT, "here's an AI, make use of it for ..." - and it magically does, without you having to write any plumbing.

[killthebuddha]

It sounds like you might have it backwards. The API spec is published by you and the AI consumes it.

[int_19h]

It should read "here's an API", of course.