Under the hood, it's quite similar to function calling. A few differences:

- Structured Outputs is a bit more straightforward. e.g., you don't have to pretend you're writing a function where the second arg could be a two-page report to the user, and then pretend the "function" was called successfully by returning {"success": true}

- Having two interfaces lets us teach the model different default behaviors and styles, depending on which you use

- Another difference is that our current implementation of function calling can return both a text reply plus a function call (e.g., "Let me look up that flight for you"), whereas Structured Outputs will only return the JSON

(I worked on this feature at OpenAI.)

I guess practically this will be the equivalent to function calling with a single tool. The AI splits out some payload that you presumably feed into whatever you do next. There are only 2 possible outcomes: can/cannot produce payload, which is equivalent to call/not call the next functionality.

With function/tool calling, you give it a list of tools with payload and the AI will select between them, or refuse, so there are more than 2 possible outcomes.

(I've never used any of these APIs, get that from just reading the docs)

Function calling uses JSON mode. While it has been mostly correct, I do get an incorrectly formatted response sometimes (maybe 1 in 10k requests?). So it sounds like this fixes that bug.