Asus has officially announced the list of Zenfones getting Android 6.0 Marshmallow update, which includes popular model Zenfone 2. Though Asus has not mentioned the exact ETA, the update is expected to arrive in May – June 2016, so Asus Zenfone owners have not got long to wait to enjoy the new Marshmallow features.
Besides the Marshmallow native features such as the Personalized app permissions, Android Pay, new Fingerprint features, Doze mode for prolonged battery life, Google Now on Tap, the update will replace three ZenUI apps – Asus Messenger, Asus Mail and Asus Calendar to Google Messenger, Calendar, and Gmail.
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)
ZenFone Zoom (ZX551ML)
As mentioned above, the Android 6.0 Marshmallow OTA (over-the-air) updates update is expected to arrive sometime in the second quarter of 2016 on these devices.
Once you upgrade your Zenfone to Android Marshmallow, your phone become incredibly fast and fluid. You can check for the update by going to phone settings under About phone. (Source)