Ubuntu 16.04 LTS Shown in Upgrade Manager Now

I see the next upgrade available as 16.04 LTS shown in update manager.

But the release date (from wiki) is written as April 2016. And it's not shown in Ubuntu page yet.

Why is it already available to upgrade now? If it's not official, why is it listed as an option in the update manager?

Thanks for any information.

(I'm in the process of upgrading my Ubuntu Gnome 14.04 in my Dell Venue 11 Pro 7140. Everything works, except sound, and modprobing my snd_soc_sst_broadwell fails - whereas in Ubuntu (main) 15.10, it works- , hence wanted to upgrade and came across this issue.)

update-manager -d checks if upgrading to the latest development release is possible. Since 16.04 alpha 1 release is available from January 7, you'll be notified about this.

Read this post to know how to upgrade your system. Your best bet would be to use a 15.10 live USB.