During the tests of new vSphere 6.5 you will quickly realize that the virtual machine created in compatibility mode for 6.5 has VM Hardware Version 13.

It could be quite strange in case we had version 11 in vSphere 6.0. Perhaps it means that VMware at first planned to release vSphere 6.1 which would use VM Hardware 12 but finally skipped it in favor of the vSphere 6.5.

Anyway to be able to use new features of vSphere 6.5 you are obliged to use VM Hardware 13.

By the way current version for VMware Tools is 10.1