Android 5.1 introduces a small set of new APIs for developers,. Android 5.1 brings the platform up to API level 22. This includes new APIs for devices with more than one SIM. In addition, there is a newly added support for “Carrier Services,” which allows cellular providers to build apps that modify provisioning tasks, like setting the correct IP addresses for data connections.
The SDK now includes Android 5.1 emulator system images that you can use to test your apps and develop using the latest capabilities and APIs. You can update your SDK through the Android SDK Manager in Android Studio. Google also said that it will start rolling out updates for Android 5.1 to the following Nexus devices: Nexus 4, Nexus 5, Nexus 6, Nexus 7 , Nexus 7  (3G), Nexus 7 (2013), Nexus 7  (3G/LTE), Nexus 9, Nexus 9 (LTE), Nexus 10, and Nexus Player over the next few weeks.