After getting into a legal battle with Cyanogen Inc., OnePlus figured it would be best to start afresh with a new OS for the phone, which was later announced to be OxygeOS.
The Chinese market will get a different OS this time around too in the upcoming HydrogenOS. HydrogenOS for the One will be announced in the Chinese capital of Beijing on the 28th of May.
Very much like the international flavour i.e., OxygenOS, HydrogenOS too is expected to be a lightweight system with focus on battery life and performance.
HydrogenOS will be based on Android 5.0 Lollipop, and as you would expect, feature some tweaks and tricks to differentiate it from vanilla Android.