> They’re nondeterministic at a fine level, but can be “deterministic” at a more general level: e.g. you might know that one model will always return properly formatted json when asked. That might not be true of the replacement, even if it is in general “better” and cheaper.

This isn't true. Even Sol messes up JSON formatting for me on occasion.

Do not delude yourself into thinking these things are reliable. They are not.