vCenter Server 8.0 supports VASA API version 4.0. However, after you upgrade your vCenter Server system to version 8.0, the VASA API version might not automatically change to 4.0.
8.0 Upgrade 3F and Below
Workaround:
Unregistering and re-registering the VASA Provider on vCenter will re-establish new session with the VASA version latest supported by VASA Provider and switch to 4.0.
This issue is resolved in 8.0 Update 3G