Apple is promoting a new feature on the Apple TV, the ability to jump right to a live broadcast in certain TV apps that feature live streaming video. Currently promoted with CBS, ESPN, and Disney XD, the feature allows you to use the Siri remote to say, for instance "Watch CBS" to be taken immediately to a live from CBS.
Apple states the following on the Apple TV's "What's New" section under Settings > System:
Ask Siri to start watching a live channel from one of the supported apps, such as CBS, Disney XD, and ESPN. Try saying "Watch CBS" or "Watch ESPN live".
Currently, Apple is only saying that the live tune-in feature is available with the above-mentioned apps, and it does not seem to work with other live streaming apps, such as ABC News. Note that these apps require either a subscription of their own or a cable login in order to watch live video.