How to stream live Apple Event on Apple TV (4th gen)? Apple provides this web page announces live streaming for tomorrow’s Apple Event on 2016-03-21.


  Join us here on March 21 at
  10 a.m. PDT to watch the keynote live.
  
  Requirements: Live streaming uses Apple’s HTTP Live Streaming (HLS) technology. HLS requires an iPhone, iPad, or iPod touch with Safari on iOS 7.0 or later, a Mac with Safari 6.0.5 or later on OS X v10.8.5 or later, or a PC with Microsoft Edge on Windows 10. Streaming via Apple TV requires an Apple TV (2nd or 3rd generation) with software 6.2 or later or an Apple TV (4th generation).


That last line mentions streaming on an Apple TV. But how? What app to use?
The App is called "Apple Special Event".

Have a look at: Apple Events app brings March 21 keynote to Apple TV