Steam News announces a new update is now automatically available for Left 4 Dead that adds the free Crash Course DLC to Valve's co-op zombie shooter. They also announce Left 4 Dead is on sale for half-off for the next three days, and they are offering a Left 4 Dead 4 pack so you can gift your friends with copies of the game. Update: The price on the four-pack has now been corrected to $44.99 USD, reflecting the sale. Here's word on the DLC and the sale:

Crash Course delivers new single-player, multiplayer and co-operative gameplay and bridges the storyline between the No Mercy and Death Toll campaigns in the original game. To celebrate, we are offering Left 4 Dead at 50% off for 3 days. Or share the fun - get the Left 4 Dead Four Pack and give the game to your friends.

While containing both Survival maps and a Co-operative Campaign, the primary goal of Crash Course is to deliver a complete Versus mode experience in just 30 minutes, resulting in a streamlined version of the game's existing Versus campaigns.

Learn more about the free, all-new free Crash Course DLC on the Left 4 Dead Blog.