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http://www.pcgamer.com/2014/05/27/xcom-enemy-unknown-coming-to-linux-steamos-this-summer/?ns_campaign=article-feed&ns_mchannel=ref&ns_source=steam&ns_linkname=0&ns_fee=0

From the article:

The Linux version of XCOM: Enemy Unknown will be a SteamPlay title running under Ubuntu 14.04 and SteamOS, and will include the original game plus the Slingshot and Elite Soldier DLC packs. More significantly, it also includes the XCOM: Enemy Within expansion that adds new base facilities, weapons, research projects, upgrades, and of course plenty of new and interesting ways to die at the hands of the rapacious alien invaders.
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GOGwiiisfun: The Linux version of XCOM: Enemy Unknown will be a SteamPlay title running under Ubuntu 14.04 and SteamOS, and will include the original game plus the Slingshot and Elite Soldier DLC packs. More significantly, it also includes the XCOM: Enemy Within expansion that adds new base facilities, weapons, research projects, upgrades, and of course plenty of new and interesting ways to die at the hands of the rapacious alien invaders.
Does this mean that if I have the base game, I will receive the DLCs for free? Just dreaming :D