Until now, Google Assistant has been limited to the Google Home and the Pixel phones (unless you edited your phone’s build.prop file). Assistant is slowly making its way to more devices, starting with Android TV. “In the coming months,” it will become available on all Android TV devices in the US running Android 6.0 Marshmallow or higher (sorry, ADT-1 owners).
Assistant on Android TV is similar to Google Home paired with a Chromecast, allowing you to play content from supported services (like YouTube, Netflix, Google Photos, etc) with a simple voice command.
Google Assistant coming to Android TV, more actions in development was written by the awesome team at Android Police.