Nexus 9 is getting a well-deserved update to Android 5.0.2 today. If you were expecting 5.1, you’re out of luck. If there’s an Update icon on your device, it’s not gonna be the most recent Android OS.
This OTA is rather small as it is only a bump from 5.0.1 and it brings the device to build number LRX22L. The update is 23MB in size and there are no big changes except for some bug fixes. You can get the update from the source link below. Bear in mind, you need a stock version to run on your device in order to flash 5.0.2.
Source: Nexus 9 OTA