When It was launched it came with Android Lollipop out of the box and it worked pretty well but now the Phone recently got the Android 6 Marshmallo update which made the phone more smoother and added many more features like battery saving modes and a bunch of more usefull features.
The specifications are not too great for todays phones but it is surprising that despite not having too high specs the phone can handle all heavy apps and games effortlessly! Highly Recommended!