Comcast has released the Xfinity Stream app for tvOS. It’s free and supports both the Apple TV 4K and Apple TV HD. Here’s how it’s described:
Turn any screen into a TV with the Xfinity Stream app––included with your Xfinity service.
You never have to miss must-watch TV. Stream top networks, live sports and news, plus thousands of On Demand shows and movies on any device.
• Watch up to 250+ channels of live TV on the go and your entire channel line-up at home
• Schedule DVR recordings from any device
• Access thousands of shows and movies to stream On Demand
• Download your recordings and movie library to watch offline
• Start watching right after order, and get your full set of channels and features as soon as your services are activated in your home.