I'm not quite sure the status of it at least, but reported back in 2017 that they are moving off Xen https://www.theregister.com/2017/11/07/aws_writes_new_kvm_

I'm not quite sure the status of it at least, but reported back in 2017 that they are moving off Xen https://www.theregister.com/2017/11/07/aws_writes_new_kvm_based_hypervisor_to_make_its_cloud_go_faster https://www.theregister.com/2017/11/07/aws_writes_new_kvm_ba... It could be that it's not all over and tied to specific machine types still, or there's something they've done to make it report to the guest still that it's xen based for some compatibility reasons.