For a long time, I was relying on such guaranteed structured outputs as a "secret sauce" that only works using llama.cpp's GBNF grammars. Now OpenAI literally introduced the same concept but a bit more accessible (since you create a JSON and they convert it to a grammar).
Those of you who have used GBNF, do you think it still has any advantage over what OpenAI just announced?
root ::= \" \" item{{{min_count},{max_count}}}
item ::= [A-Z] [^\\r\\n\\x0b\\x0c\\x85\\u2028\\u2029.?!]+ [a-z] (\". \" | \"? \" | \"! \")
This kinda works if you don't mind no abbreviations, but you can't do something like this with JSON grammars afaik.
But yeah I mean, GBNF or other structured output solutions would of course allow you to supply formats other than JSON schema. It sounds conceivable though that OpenAI could expose the grammars directly in the future, though.
And this is more esoteric, but technically in the case of JSON I suppose you could embed a grammar inside a JSON string, which I'm not sure JSON schema can express.