Today a jailbreak for the Apple TV 4 and tvOS 1.2-1.3 was released by the Electra team thanks to nitoTV and Jaywalker for the tvOS port. Below is a guide on how to Jailbreak your Apple TV 4:
1) Connect your Apple TV 4 to your computer via USB-C.
2) Download Cydia Impactor for Mac, Linux, or Windows to your computer, and open it.
3) Download the Electra v1.0.4 app from here.
4) Ensure that Impactor is showing your Apple TV as connected in its interface, and then drag the Electra.ipa file onto the Impactor window.
5) Hit Start and Impactor will prompt you for your Apple ID and password. Enter them. If you have two-step verification turned on for your Apple ID account, you cannot enter your normal password. Instead, log in to the Apple ID page, and request an app-specific password. Enter that into Impactor in the password field.
6) Impactor will now push the jailbreak app to your Apple TV 4. Once it’s complete, disconnect the Apple TV from your computer and connect it to your TV via HDMI.
7) The Electra app should now be visible on your tvOS home screen. Launch it.
8) Hit Jailbreak
9) Wait for the tool to do it’s job and once it has finished launch the new NitoTV app to enjoy new content.
If you are on 10.2.2 and want to go to 11.3. (You need blobs and MUST be on 4th gen AppleTV) follow this guide from nitoTV:
On your TV
1. reboot your appletv,
2. open #backr00m and double tap the play/pause button.
3. turn on kppless mode.
4. ssh in to your appletv (ssh )
5. get your generator from your blob (ie 0x0000000000000000)
6. nvram com.apple.System.boot-nonce=YOUR_NONCE_HERE
7. nvram auto-boot=false
On your machine
1. plug your appletv into your computer
2. Get BuildManifest and SEP from 11.4 or 11.4.1 and ipsw for 11.3
3. use futurerestore to restore to 11.3 ie future_restore -t your_blob_file.shsh -s sep-firmware.j42d.RELEASE.im4p -m BuildManifest.plist -w AppleTV5,3_11.3_15L211_Restore.ipsw –no-baseband
If you are not on a jail breakable firmware thankfully you can downgrade your Apple TV to tvOS 10.2.2 using the ispw from here.