The One M8 might be getting Lollipop update which is Android 5.0 but Google Play Edition of same model is now seeding the Android 5.1 update. The update is available via Over the Air download and it's file sized at around 244 MB. Earlier to this Moto G and LG G Pad 8.3 has already got this update.This update to One M8 GPE is available via Over the Air download. So on your phone head on to Settings > About Device > Software Update and then hit Check Now. If the update is not available then we recommend to head over - how to manually flash One M8 GPE with Android 5.1.
Google launched Google Play Edition smartphones in order to provide stock Android experience on selected popular phones. Among the available GPE models are -
So, it's Galaxy S4, XPeria Z Ultra just left to get this 5.1 update. Do checkout whether your phone is eligible for Android 5.1 Lollipop update or not.