Stock AOSP Android is pretty awesome on the Nexus 9, but part of the reason you buy a Nexus device is so you can tinker around with it. If you are like me then you are itching to install a Rom on your shiny new toy. The only issue with that is that we still don't even have a custom recovery. No worries developer "Craigacgomez" who is known for the Nexus 10 Thunderkat rom has released a new rom that can actually be manually flashed as system.img using adb commands. This may not be the most user friendly way to install a Rom, but this is the first custom Rom released for the Nexus 9! A few features include a 5.0.0_r2 LRX21M base, AppOpps enabled, Ambient display enabled, Root friendly stock kernel, Added 64 bit busybox, enabled google location services, and more. It should be noted that this rom is not rooted so you will need to reroot after install. This is a fully deodexed build so the first boot may take a long time, just be patient. Head to the link below for the Rom download.
via XDA