The Sacrifice

 is an upcoming DLC for both Left 4 Dead and Left 4 Dead 2. If downloaded for Left 4 Dead, you will gain a new campaign, called The Sacrifice, which is played as the original Survivors, and end with a member of the team sacrificing themselves. If downloaded for Left 4 Dead 2, however, you will gain The Sacrifice, along with No Mercy being playable. If downloaded for Left 4 Dead 2, the Sacrifice and No Mercy will be played as the original Survivors, but retain all the new weapons from Left 4 Dead 2, such as the M60 and Katana and Left 4 Dead 2's Special Infected.