Electronic Entertainment Expo (E3) - Xbox One developper explains it.

When you fail to connect to Steam (which will be the case if you don't have a connection), it will provide an option to switch to offline mode. Then you can play any games you have valid "account credentials" to. Account credentials are verified only once at the time the game is done downloading and then it will be saved in your Steam folder as long as you don't delete it, no daily checking. When you launch the game, it'll search for local account credentials first before making any connection to generate one. Logging in from another device will require a 1-time verification by checking your email and get the verification code, no hourly checking. If you copy the entire Steam folder along, account credentials don't even need to be verified and you can play the games right away in offline mode.
Additional DRM methods are left to the publishers and not mandated by Valve. Steam itself uses 1-time activation in the most transparent way.