The Xen 3.4 release contains new features compared to the 3.3 release as listed below:
RAS features: cpu and memory offlining
Power management: improved frequency/voltage controls and deep-sleep support. Scheduler and timers optimised for peak power savings.
Support for the Viridian (Hyper-V) enlightenment interface
Many other changes in both x86 and IA64 ports.
You can download this new version from their official website
http://www.xen.org/download/Thanks!