Android 5.1.1 & Android M
It looks like the Samsung Galaxy Note 5 will feature one of two operating systems. Either the Android 5.1.1 update that Samsung's rolling out right now or Android M, the new operating system that Google's planning to push out as early as August.
Android 5.1.1 is the most stable version of Lollipop yet and Android M is focused on improving performance and Android's code. Both are extremely exciting, extremely important updates and that's key for prospective Galaxy Note 5 buyers.