Sledgehammer Games finally announce that the weapon that will be in the first DLC will be having ealy access for those only that hold the season pass. That means that if you buy the Season Pass you will be having an early access to this weapon. The Release Date will be on January 13th. For more info check this webpage:

http://charlieintel.com/2014/12/23/psn-season-pass-owners-get-access-ae4-ae4-widowmaker-weapon-january-13th/

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The release of the first DLC is coming to Advanced Warfare in 27/1/2015 in Xbox 360/Xbox One and one month later on PC/PS3/PS4. It includes:

1. 4 new maps (Sideshow, Core, Grift, Urban)
2. A new weapon (AE4-AE4 Widowmaker)
3. The new CO-OP Exo-Zombies Mode