Microsoft have overnight made Windows Server 2016 RTM to download from the MVLS portal. This is the final code, bar any last minute Windows Update patches.
After testing the Windows Server 2016 techincal preview, i think this is going to be a really exciting release (As a virtualization specialist, my particular favourite is the new Storage Spaces Direct feature!).
Both the 180 day trial of Server 2016, and the final release of the free hypervisor, Hyper-V 2016 can be downloaded from Microsoft’s site.