OnePlus has announced their plans to bring Marshmallow to their smartphones. The OnePlus One and the OnePlus 2 will receive the update in Q1 2016, there is no specific date as of now which means the update will be rolled out from Jan 1st 2016 to March 31st 2016.
As you know, the OnePlus One doesn’t comes with Oxygen OS by default so there is no timeframe but the company said that it will work on the community build when time permits.
Whenever the Marshmallow update rolled out for OnePlus 2 it will comes with standard Marshmallow fingerprint sensor API. OnePlus also revealed that they are working on the update to Marshmallow for the OnePlus X but they haven’t revealed a time frame as of now but we are guessing that it would be only after the OnePlus One and OnePlus 2 receive their updates first.