The rumored collabortation between Valve's Left 4 Dead team, and Payday: The Heist's Overkill Software, didn't turn out to be everything we hoped it would be, but it still ended up being pretty cool nonetheless.
First the good news, the collaboration will involve a crossover of Left 4 Dead and Payday. It is not, however, a full prequel to the Left 4 Dead series as was rumored. It will instead be a single downloadable mission for Payday that takes place in Left 4 Dead's "Mercy Hospital."
Right now, Valve is saying that the mission is not a canonical prequel, but that it will feature a brief cameo from one of Left 4 Dead's characters. "This is a 100% Overkill made mission forPayday: The Heist simply set in Mercy Hospital from the Left 4 Dead series," Valve told Shacknews. "It is not telling the origins of the Infection and is not canon. There is a little cameo from one of the L4D characters (the comic should give you a hint) and a fun little easter egg with a payoff later in Left 4 Dead. Just us having some fun with a we are friends with and who have also made a great co-op game."
The trailer - which originated this information - was briefly posted online before being taken down, however you can still view it on Shacknews. It portrays the DLC level as a prequel to Left 4 Dead, but Valve has said that is merely the result of over-excited marketing people taking things a step too far.