After finding themselves caught up in the CyanogenMod – Micromax fiasco, OnePlus announced that they would be rolling out their own ROM in December 2014. Taking advantage of the timezone, one would imagine, OnePlus have managed to do that.
The Lollipop update for the OnePlus One is now out, but there’s a catch. The ROM isn’t CyanogenMod based, and is in its nascent stages so there are going to be some bugs. According to OnePlus, the ‘build contains no extras beyond the stock features of AOSP Lollipop’; so you’re probably only going to see a new Android version in the about phone tab more than anything else.
Also, you have to have TWRP installed in order to flash this build. OnePlus also state that this build is not eligible for future OTA updates. Unless you’re a geek who’s bound to a vow to try all firmware updates from OnePlus, it might make sense to skip this one until a full-fledged stable update is available (which according to OnePlus will happen in February 2015).
Complete instructions and details about the ROM can be found at the source link below, which will take you to the post on OnePlus’ forums.Source]