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
New Mutation: Hunting Party
Fixed door exploit in No Mercy
Now Allow thirdperson settings in cooperative game modes
Fixed add-on campaigns not always appearing in the campaign selection screen
Restored dedicated server support for add-on campaigns
Fixed some rendering artifacts on Mac
Added support for Russian audio in The Sacrifice and No Mercy
Game correctly recognizes the audio language set in Steam
Get the full article at store.steampowered.com