alt Hacker NewsIME you could get reliable JSON or other easily-parsable output formats out of OpenAI's going back at least to GPT3.5 or 4 in early 2023. I think that was a bit after LangChain's release but I don't recall hitting problems that I needed to add a layer around in order to do "agent"-y things ("dispatch this to this specialized other prompt-plus-chatgpt-api-call, get back structured data, dispatch it to a different specialized prompt-plus-chatgpt-api-call") before it was a buzzword.
Can guarantee this was not true for any complicated extraction. You could reliably get it to output json but not the json you wanted
Even on smallish ~50k datasets error was still very high and interpretation of schema was not particularly good.