Pangu, the team behind the most recent jailbreaks on iOS, have just released a jailbreak for the Apple TV. There are a lot of caveats for using it, including the fact you'll need to still be running tvOS 9.0/9.0.1. In order to jailbreak your Apple TV, you'll need to be running the vanilla launch operating system of tvOS 9.0/9.0.1 and not the update released earlier this week. Beyond that, you'll also need a USB-C cable, a Mac, Xcode and a paid Apple Developer membership. Once you do jailbreak that Apple TV, all you can do is SSH into it as there's no Cydia-like app. Still, as a proof of concept, it's interesting. Though we'll see if anything useful comes with it.