Maintainer Tejun Heo sent in the cgroup changes today for the Linux 4.5 merge window. About the new interface he notes, "cgroup v2 interface is now official. It's no longer hidden behind a devel flag and can be mounted using the new cgroup2 fs type. Unfortunately, cpu v2 interface hasn't made it yet due to the discussion around in-process hierarchical resource distribution and only memory and io controllers can be used on the v2 interface at the moment."
The pull request with more details on the cgroup changes can be found via the kernel mailing list.
To learn more about the cgroup v2 interface changes, see these PDF slides. Long story short, the interfaces are dramatically cleaned up, more consistent, and more.