Just in case you were wondering what ZUK is, they are a Lenovo-backed company which rolled out their very first smartphone which is known as the Z1 not too long ago. The ZUK Z1 will runs on its own ZUI over in China, but the international model will arrive Cyanogen OS 12.1 that is based on Android 5.1.1 Lollipop right out of the box.
Since Android 6.0 Marshmallow is now available from Google, it is a no-brainer that this is set to happen as well. It is also rather likely that the international model of the ZUK Z1 too, will be on the receiving end of the Cyanogen OS 13 that is based on Android 6.0 Marshmallow when that is ready. Not too shabby at all, taking into consideration that this is a relatively new handset.