14 DAY TRIAL // Canonical pushed the latest Linux kernel 4.4 LTS into the repositories just last week, and now the latest Ubuntu builds are also integrating it.
The integration of Linux kernel 4.4 LTS into Ubuntu 16.04 LTS is an important step for the project, and it's good news for the Ubuntu kernel developers who don't have to keep an older version alive like they have done until now.
Many of the previous Ubuntu versions launched with the latest Linux kernel at that time, but the kernel developers quickly declared them EOL (end of life), so the Ubuntu team had to pick up the development and maintain that branch. This won't be the case now since Linux kernel 4.4 is an LTS branch and it will be supported for a long time.
Unfortunately, there is no information released ahead of time regarding the length of the support for Linux kernels.
Linux kernel 4.4 LTS to be upgraded before official launch
It's very likely that newer versions of the Linux kernel 4.4.x branch will be released soon. As a matter of fact, the latest and the most advanced version available right now is 4.4.1, which will probably land in Ubuntu 16.04 daily build soon, after the team does the proper testing.
It's important to mention that Ubuntu 16.04 is not stable just yet, and the launch is scheduled for the end of April. You can use it right now but not on productions machines. This is a very busy development period when a lot of changes are being made and the system will break very easily.
You can download the latest daily build of Ubuntu 16.04 LTS, and you can give it a spin, but please keep in mind that you will have to select the UEFI entry. With this version, Ubuntu only boots with UEFI enabled.