The Xbox One is not compatible with any previous Xbox games, either from the original Xbox or the Xbox 360. That includes digital games, which despite remaining tied to users' Xbox Live accounts won't be playable on the new console.
That's because the Xbox One is built on a completely new architecture, and backward compatibility is conceivably something few players take advantage of. But it's still something that some gamers will miss. And unlike Sony, Microsoft hasn't even announced any plans to implement backward compatibility, through streaming services or otherwise, in the future.