Ruby date/time handling is confusing, with too many overlapping classes, developed at different times with odd interfaces and/or semantic edge cases (not unusual on other platforms either), but I believe the things people use as default/recommended standard these days on ruby actually do support gregorian/julian changeover!

But I guess ruby is unusual there! Or I'm wrong.

But good to know most have it as opt-in, anyway!

I would need to see the APIs and examples to be able to evaluate it honestly.

(FWIW, I'm the author of a datetime library in Rust called Jiff.)