Oxygen OS is the new operating system based on Android 5.0.2, a newer version of lollipop. Many of the mobiles have been released with the lollipop versions, so to those a new update of 5.0.2 is available which is oxygen os. This os is officially released and can be perfectly installed on the smartphones. Among all its particularly now meant for only one plus one mobiles. Here you can't receive the OTA update on your device, its a manual method to run on phone. This is official update not the custom ROM and only meant for the Android one plus one. Follow the simple guide to install oxygen os on one plus one smartphone.
Before following this guide have a complete back up of your phone and memory card.