The big patch will expand the game's multiplayer to a maximum of eight online players, allowing 4 vs. 4 play in the skirmish and Theater of War modes.
The Escalation Pack adds four new maps, three unit upgrades and 10 achievements/trophies for 800 Microsoft Points ($10). The new maps will only be playable in skirmish mode.
Both the patch and the DLC will hit the Xbox 360 tomorrow, December 11. The DLC should make its way to the PlayStation Store on Thursday, while the PS3 multiplayer patch won't see release until next year.