The Left 4 Dead and Payday: The Heist crossover was revealed back in May with a trailer featured here on NGN. The update is out now, containing a new heist set in the Left 4 Dead “Mercy Hospital” setting. Also, if the player owns Left 4 Dead or Left 4 Dead 2 on steam, new zombie masks will be available for use in Payday. Finally, a cameo appearance by a Left 4 Dead character is confirmed, as well as a new “OVERKILL +145” difficulty setting for expert players to attempt.
While Valve was involved with the project, Overkill, the developers of Payday handled all development of the crossover, referring to it as their “fan fiction for Left 4 Dead“.
The update is provided free of charge to those who own Payday: The Heist, and is available now