Why Is Zod v4 Fast — and Where Is Its Ceiling?

Zod v4 achieves its speed gains primarily through a hidden JIT-like code generator ($ZodObjectJIT) that builds specialized validation functions at runtime using new Function(), targeting object schemas for 1.3-4.5x improvements over v3. While v4 traded some raw throughput on primitives and collections for a richer architecture (better errors, async support), the author extended this JIT principle into an AOT compiler achieving 3-60x speedups across all schema types.