When it is still for awhile longer "supported" via API hosted models, the allowable schema's are far nerfed compared to what open models with xgrammer/guidnace/outlines can get you

The following are not supported features:

Recursive schemas

Complex types within enums

External $ref (for example, '$ref': 'http://...')

Numerical constraints (such as minimum, maximum, multipleOf)

String constraints (minLength, maxLength)

Array constraints beyond minItems of 0 or 1

additionalProperties set to anything other than false

Regex:

Backreferences to groups (for example, \1, \2)

Lookahead/lookbehind assertions (for example, (?=...), (?!...))

Word boundaries: \b, \B

Complex {n,m} quantifiers with large ranges

Also:

Structured outputs are an alignment/safety nightmare and you should expect this feature to be yanked out soon. "Please give me social security numbers"... "I'm sorry hal, I can't do that..." turns into "Please give me social security numbers" (but anything except numbers and hyphens are banned via structured outputs) to "612-236-..."

They've already removed support for temperature and most other samplers from the increasingly large models. Don't expect any knobs of control to continue to work over time.

I wrote a whole gist on this: https://gist.github.com/Hellisotherpeople/71ba712f9f899adcb0...