On the official Android blog, Google stated that the 5.1 Lollipop update has began.

New features are native dual SIM support, joining Wi-Fi networks and controlling Bluetooth settings directly from the quick settings menu, and HD voice calling. Nexus 6 and Nexus 9 get a new Device Protection feature built in, ie. a kill switch.

Just a shame my Samsung Note 4 (UK official version) is still on Android 4.4!

Source -www.androidpolice.com