Zod 4

The big changes are straightforward: email, uuid, and url validators moved from string methods to top-level functions, and nonempty() became min(1). Beyond that, you get solid patterns for discriminated unions, transformations with coerce and preprocess, and the new error parameter syntax that replaces the old message approach. The React Hook Form integration example is handy if you're doing form validation. It's basically a cheat sheet organized around the breaking changes, so you spend less time in the docs when something that worked in v3 suddenly throws errors.