After downloading the "sizeable" software update, gamers will be able to play any map from the Left 4 Dead series, including customised ones from the original game.
The authoring tools work in the same way as on Left 4 Dead apart from a few new features - Gamemode Logic adapts each map to the mode which is being played and Director Logic makes enemy AI harder in relation to the skill level of the survivors.
The toolset also includes Scavenge Mode Support, while the Valve team has compiled an updated tutorial to guide players through the new design features.
In a statement, Valve's Yasser Malaika said: "What we want for New Year's is to get to play your custom maps in Left 4 Dead 2."
The toolset is available to download now from Steam via the tools section.