Getty
HBO's Eric Kessler made the announcement today at AllThingsD's media conference.
To be clear, HBO GO won't be available as a separate app on your Apple TV. You'll need to beam HBO GO shows to your Apple TV from your iPhone or iPad using AirPlay. However, Kessler did say a native HBO GO app is in the works for Apple TV, meaning you eventually won't need to use AirPlay.
You need to update the HBO GO app on your iPhone or iPad for the new AirPlay feature to work.
Apple TV is a bit behind though. HBO GO's app is already available for other streaming set-top devices like Roku and Xbox.