Updates to Left 4 Dead 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

Left 4 Dead 2

• Encore Mutation - Hunting Party
  
• Dead Air: The Crane - The alarm car is no disabled until you are on the street
  
• Dead Air: The Construction Site - Blocked windows to prevent early triggering of the Crescendo event