Asus has issued a list of devices that are scheduled to receive Android Marshmallow software update in the second quarter of 2016, which is sometime between April and June.
The devices that are eligible to get the Marshmallow experience are PadFone S (PF500KL), ZenFone 2 (ZE550ML, ZE551ML), ZenFone 2 Deluxe (ZE551ML), ZenFone 2 Deluxe Special Edition (ZE551ML), ZenFone 2 Laser (ZE500KG, ZE500KL, ZE550KL, ZE551KL, ZE600KL, ZE601KL), ZenFone Selfie (ZD551KL), ZenFone Max (ZC550KL) and ZenFone Zoom (ZX551ML).
The list Asus put out in November 2015 for Marshmallow update contained most of the devices present in the new list, apart from a few more. The new list again misses out the ZenFone 4,5 and 6, which were launched in 2014. This means Android Lollipop would be the last major Android upgrade for them.
Along with the latest Android version, ZenFone users would get a bunch of goodies. The Marshmallow update will replace Asus native apps such as Asus Messenger, Mail and Calendar with Google's version such as Google Messenger, Calendar and Gmail apps.
Once you perform a factory reset after the update, Google apps will be set as default apps. But if you like the Asus apps over Google's, you can always download them from the Google Play Store. Head over to the Asus official forum to know more about the update.