 On November 9, 2009, a matchmaking update to allow for matchmaking between teams of four players in versus mode was released.An add-on campaign for "Left 4 Dead 2", "The Passing", featured the "Left 4 Dead" survivors meeting the new cast as part of a full campaign.The "Left 4 Dead 2" content was set for release in March 2010, however it was delayed until April 22, 2010.