Joseph Salisbury, one of the Canonical developers, have announced that they have rebased the master-next branch of Ubuntu 16.04 LTS Xenial Xerus to Kernel 4.3, but the Ubuntu devs are tracking Kernel 4.4, to use it by default on the final version of Ubuntu Xenial.
The Ubuntu Kernel developers have added Kernel 4.4 RC4 to the unstable repositories of Ubuntu 16.04. As a reminder, Ubuntu 16.04 LTS is scheduled for release on April 21, 2016, but the alpha version is expected to arrive on December 31, for both Ubuntu and official flavors: Kubuntu, Xubuntu, Lubuntu, Ubuntu GNOME, Ubuntu Kylin, and Ubuntu MATE.
The official announcement:
“Our Xenial master and master-next branch have both been rebased to v4.3. A v4.3 based kernel is now officially available for testing from the archive, linux-4.3.0-2.11. Please test and let us know your results. Our unstable repo has been rebased to track v4.4-rc4 in parallel. We will eventually transition both our Xenial master/master-next branches to v4.4 since that is our target kernel version for 16.04,”