Co-founder of OnePlus One, Carl pei, recently made it clear through a tweet that OnePlus One devices will get the Android Lollipop update in March. The firm which made commitments of making the Lollipop version available in the next three months is already late by a month.
The International version of OnePlus One will get a update of CM 12 which is developed by Cynogen via OTA. Also the first stable version of Oxygen OS, OnePlus's own OS, will be realeased next month along with the CM 12 update. Now it is upto the users whether they wish to continue with the Cynogen Mod or wipe everything and start a fresh with the Oxygen OS.
@rajarshi_10 We released an L alpha a while ago, but a more stable build (OxygenOS & CM12S) will need to wait until March. Sorry for delay!
— Carl Pei (@getpeid) February 23, 2015