Google has quietly made a background update to Google Assistant that allows you to link your HBO NOW account to it. That means that you can stream content from the service to your Chromecast devices simply by asking Assistant to do so via your phone or Google Home.
HBO NOW is the stand alone streaming service from the premium movie service. It is $14.99 per month and is for cable cutters who do not have a cable or satellite subscription. For those that do have HBO as part of their cable package, the app to stream content on your Android device is HBO GO but that cannot be connected to Google Assistant.
The addition of NOW means that if you are a subscriber, you can give Google Assistant commands to play content on your Chromecast enabled TV. For example, you can say, “OK Google, Play La La Land on my TV”and it will play the movie from HBO on your Chromecast enabled TV. If you have more than one enabled TV, you will need to specify which one (but usually Google Assistant will ask you to clarify).
With this addition, you can now stream content from Google Movies & TV, CBS All Access and Netflix. To set it up, just go to the Google Home app, tap the menu and go to More Settings then down to Videos and Photos.