Just seen this on Xbox.comBuy Dead Rising 3 digitally on your Xbox One or Xbox.com between 27/01/14 and 09/02/14 to receive a code via email that can be redeemed for World War Z in HD to own on Xbox Video. Code can be redeemed between 27/01/14 and 28/06/14.
Visit xbox.com/zombieweek/terms for full terms and conditions.
I think that's a pretty damn good deal myself.
Dead Rising is a great game and i really enjoyed World War Z, if I didn't have them both already i would so be getting them.