Hey, I did some benchmarks if you're interested - benchmarks results are in the README.md.
https://github.com/nimeshnayaju/zod (Fork of Zod's repo which already included benchmarks comparing Zod 4 against Zod 3, so I simply integrated my validation library)
Yes, the primary focus is memory efficiency; performance improvement is a side effect of that. From my own benchmarks, I have found that to be the case. If you're validating thousands of objects per second or working with memory constraints, the difference becomes quite significant. Happy to share the full benchmark code if you'd like to run them yourself!