Google has recently started rolling out Android 5.1.1 to the Nexus 10 and Nexus 7. While the update contains many bug fixes and small improvements we don’t expect Google to roll out this update to any other Nexus device soon.
Cyanogen has just released CM12.1 20150507 Nightly based on Android 5.1.1 which means that by installing the latest Cyanogenmod 12.1 Nightly you can install Android 5.1.1 Lollipop on your device. Android 5.1.1 CM 12.1 Is compatible with the following devices:
If your device is on the list, head over to the official Cyanogenmod page and download the latest CM12.1 20150507 Nightly here