Yesterday we announced that the Nexus 9 is finally receiving the OTA update to 5.1.1 and that you can actually download the ota.zip for applying manually if it hasn't rolled out to your device yet. However applying that official ota update does require you to return your Nexus 9 to stock Android with stock recovery. If you are currently running a custom recovery like TWRP there is an easier way. Developer "craigacgomez" has released his own build of stock 5.1.1. His build is based off of official AOSP and only includes a few tweaks for improved user experience. This rom can be flashed in custom recovery so there is no need to return your device to stock! Head to the link below to grab the Rom file.
via XDA