Starting in Windows Server 2012 R2 you now have a way to upgrade a cluster to Windows 2016. The best part is it’s not an OS upgrade, but a rebuild. The magic is that you can join a Windows 2016 server to a Windows 2012 R2 cluster. You can upgrade your cluster with as little as one failover and thus very little down time. Everything stays in compatibility mode until all nodes are upgraded to Windows 2016 and then you upgrade the cluster functional level. This is great news for those of us running FCIs or AGs.
Click through for a listing of steps and a video.