If you took the plunge on one of those new LTE Nexus 9s earlier today, you'll be happy to know there's a factory image waiting for you. That makes restoring the device to stock a snap. All you need is a computer, a USB cable, and an unlocked bootloader.
The image is Android 5.0.1, build LRX22C. The code name for the LTE Nexus 9 is "volantisg," which is expected. All the previous Nexus tablets with mobile data simply added a "g" on the end. It's a 835MB download, but you might want to keep it handy if you plan to do any tinkering.