ZUK’s co-founder Chenyu had revealed a few days back that the domestic version of the ZUK Z1 running on ZUI will be upgraded to Android 6.0 Marshmallow by March 2016. He added that the company had already started on the adaptation work of the new Android version to the device.
However, this presented another question. Will the ZUK Z1 International version too be upgraded to Android 6.0? At that time, we weren’t sure of this, but according to the latest news, the international variant will also be upgraded to Android 6.0. This particular version runs on the Cyanogen OS 12.1 based on Android 5.1.1. It is said that Cyanogen is working on the Android 6.0 based Cyanogen OS 13 and ZUK Z1 International version will be one of the first devices to get the update.
Unfortunately, at this moment, there’s very little information regarding the Cyanogen OS 13 update. But given that the Chinese variant of the device is supposed to get the update sometime after February, you can expect the same release time frame for the international variant as well.
We will keep you guys updated if more information comes up in the next few weeks.[source]