As Olin mentions in the tweet, you can pre-purchase the DLC right now through Steam. Though you don't strictly need to secure your copy of a digital-only product ahead of time, since there's no concern about scarcity, you do save $1.50 by doing so.
Posted on Sep 20th 2014 11:30AM
Posted on Sep 19th 2014 8:00PM
Posted on Sep 19th 2014 6:30PM