Both OnePlus One and 2 will receive Android M updates via Cyanogen OS in the first quarter of 2016. Meanwhile, a community build version of OxygenOS for Oneplus One is also expected to feature sooner.
OnePlus 2 users will additionally receive the new standard Marshmallow API for the fingerprint Sensor.
Oxygen OS will not receive any API support for the fingerprint sensor as OnePlus will soon implement Android M in all devices. But OnePlus has promised to roll out Android M for OxygenOS sooner.
The road seems to be dim for OnePlus X as the smartphone-maker is still working on “possible updates in a later time frame”.[Source]