OnePlus has officially laid out some details as to when the OnePlus One and OnePlus 2 will be receiving the update to the latest version of Android, Marshmallow.
Posted on the OnePlus forum, both the OnePlus One and 2 can expect Marshmallow in Q1. While no specific dates were given, that means at the most OnePlus users have around 4 months to wait.
Marshmallow for the OnePlus One will be coming in the form of Cyanogen OS, while the OnePlus 2 will continue to run OxygenOS with a few tweaks, like the addition of Google’s standard fingerprint reader API.
OnePlus didn’t have anything to share on the OnePlus X right now, but more info should be coming soon.

Source :
Androidandme