As a result of his hardware manipulation, zeroepoch has successfully developed a software rooting method for the 2nd-gen Fire TV. To root the new Fire TV 2 using this method, your device must be on software version 18.104.22.168. The rooting instructions are only outlined for Linux computers right now, but can work on Macs with some modifications. You will also need an A-to-A USB cable to use to connect the Fire TV to your computer.
This new rooting process is not trivial and not easy for a novice user to attempt. This is why I haven’t written a guide for this rooting method yet. As additional experienced Linux users use this method to root their Fire TV 2, issues surrounding this process should be ironed out which should make it accessible to more people, at which point I will write a guide. In the meantime, if you want to root your 2nd-gen Fire TV, you should let it update to software version 22.214.171.124 (534011720) as soon as possible and then block software updates. Once Amazon releases a newer software update, you will not be able to update to 126.96.36.199, and it’s not clear right now if this rooting method will work for future software versions.
Here is my Fire TV 2 Rooting Guide:
How to Root the Amazon Fire TV 2