The USB Implementers Forum (USB-IF) has finalized the specification for USB4. A few things are different this time around including the way the it named, as well as its support for another standard in the form of Thunderbolt 3.
https://www.notebookcheck.net/USB4-spec-finalized-brings-Thunderbolt-3-compatibility-and-speeds-up-to-40-Gbps.434123.0.html