There's CPU specs at:

https://www.apple.com/mac-pro/specs/

Most of the specs sound like Cascade Lake parts, but the cache sizes don't quite match. It's possible that Apple's using a custom part, or one which Intel hasn't announced yet.

It’s most likely the leaked [1] but not yet announced Xeon W-3xxx.

[1] https://www.tomshardware.com/news/intel-xeon-cascade-lake-w-...