Although you can run Android 5.0 Lollipop on your OnePlus One right now by flashing a nightly build of CyanogenMod 12S, those looking for a more stable verison have to wait until March. That's according to OnePlus co-founder Carl Pei, who revealed on Twitter that the Lollipop update would be available for both the global variant, which would receive a stable build of CyanogenMod 12S, as well as the Indian model, which will get the vendor's own OxygenOS.
@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
When Google announced Android 5.0 last year, OnePlus stated that it would make the update available within three months on the OnePlus One, with an OTA planned for the month of February. Pei mentioned on Twitter that the reason for the delay was due to "proprietary drivers, code, QA, certifications."
Source: Twitter (Carl Pei)