The OnePlus Company had unveiled that the OnePlus One and OnePlus 2 will get Marshmallow update (Android 6), in fact it has entered the final test phase. Though the final date has not been confirmed, it should happen pretty soon.
Good news for those using the OnePlus One and the OnePlus 2 smartphones. These handsets are entitled for the latest Marshmallow update and OnePlus Company is working on it. The upcoming Cyanogen OS 13 is in final stage of testing (also depends on other parties).
The company also rolled out Oxygen OS 2.2.1 on the OnePlus X handset. This Oxygen OS update size is around 284MB. It comes with bug fixes and overall optimization. This is an over the air update.
So OnePlus One and OnePlus 2 users stay tuned you will soon get the Marshmallow (Cyanogen OS 13) update.