Deepkit Type is a full-featured TypeScript runtime type system that can be used for validation, serialization, and more. It is not only a validation library, but a full-featured runtime type system that can be used for much more.
While you define your schemas in Zod & co using a custom DSL with an expensive type inference step, Deepkit Type uses just TypeScript types and enriches the type system with Type Annotations to allow to define validation constraints. This way it's much more powerful as it allows the expressiveness of TypeScript types and does not force you to learn a new DSL.