As announced by Microsoft’s Major Nelson, additions to the library for today, January 26, include Rocket Knight and Shadows of the Damned. If you already own these games for Xbox 360, they should show up automatically in your Xbox One game library. If not, you can buy them on your console or via the Xbox.com download links below.
There are more than 300 Xbox 360 games playable on Xbox One via backwards compatibility. You can see a list of all the backwards compatibility games here.
In more recent news, Microsoft announced that players collectively spent 265 million hours playing Xbox 360 games on Xbox One in 2016.