According to GridToday yesterday
XenSource Inc., the leader of the open source Xen virtualization project and a provider of enterprise virtualization solutions, today announced the release of Xen 3.1. The latest release of the Xen hypervisor delivers features to support the most demanding enterprise virtualization use cases, and open, standards-based management interfaces for the ISV ecosystem.
In addition to other features Xen 3.1 supports live relocation of virtual machines, an API for ISV development, and an enhanced 64 bit hypervisor.