Hi. Looking into the configuration of Samsung Galaxy Note 4, I think both the versions of Android OS, 32 and 64 bit are open to all mobile manufacturers. The hardware of Samsung Galaxy Note 4 is 32 bit and still it is upgradable to Android M. I think Samsung is giving this upgrade since there are significant amount of left over stocks. Moreover, Samsung Galaxy Note 3 is upgradable only till Android Lollipop.