“Those who pre-purchase the game will be able to start playing immediately upon its release on Steam.” Said Valve, owner of the Steam and Steamworks brands.
Valve went on to say: “The PC version of the product will be powered with Steamworks for both the digital and tangible versions of the game and, as with all Steamworks titles, offline play will also be supported along with Auto-Updating, Achievements, and more. Call of Duty: Modern Warfare 3 will also support dedicated servers on day 1. ”
Full steam support seams to be included, including dedicated servers. We can expect this to be a collaboration for the next titles in the series as well.