ASUS is lagging behind where the Marshmallow update roll out is concerned and it doesn't seem like the situation will improve for few more months.
ASUS has now made an announcement related to its Android 6.0 Marshmallow roll out schedule on its forums. The company has detailed a selection of eight of its phones that will receive the software upgrade to Android Marshmallow in Q2(April-June) 2016. The list includes the seven Asus ZenFone models and the PadFone S transformer. The only difference between this new list and the previous one they revealed in November is the ZenFone Selfie and the ZenFone Max additions.
The full breakdown along with the model numbers, goes as follows: PadFone S model number PF500KL; ZenFone 2 with ZE550ML and ZE551ML model numbers; the ZenFone Zoom ZX551ML version; ZenFone 2 Deluxe with ZE551ML, ZenFone Max tagged with ZC550KLmodel number; ZenFone 2 Deluxe Special Edition complemented with ZE551ML model number; ZenFone Selfie featuring a ZD551KL model number; and finally, the ZenFone 2 Laser with either one of these model numbers ZE500KG, ZE551KL, ZE550KL, ZE601KL, ZE600KL, ZE500KL.
ASUS didn't reveal the specific dates to expect this update other than the Q2 2016 time range. Once the update hits devices, ASUS has confirmed that ASUS's Messenger, Mail and Calender will give way to Google's Messenger, Gmail, and Calendar.