ZUK co-founder Chenyu has just announced via his Weibo page that the company has started on the development of Android 6.0 Marshmallow update for ZUK Z1. At present, the update is being adopted for the domestic version of the device. However, since the domestic version will receive the update next year, we also expect the international version to get the update sometime in 2016.
The domestic version of ZUK Z1 features the company’s own ZUI operating system based on Android. On the other hand, the international variant comes with CyanogenOS on board. The company had already started on the Marshmallow update since Google announced it. However, Chenyu adds that there is still a lot of work to be done which will likely be completed by the Chinese New Year in February. So, domestic ZUK Z1 users can expect the Marshmallow update sometime in March 2016.
Unfortunately, we have still no official information about the Marshmallow update time frame for the international ZUK Z1 variant. [source]