Update: Techland has revealed the big surprise as a four-day crossover event in Dying Light that will confront players with increased numbers of Virals (the Dying Light name for zombies), waves of attacking hordes, and more weapons and ammo to use against them—a more Left 4 Dead-style experience, in other words. Three Gold blueprints for Left 4 Dead 2 weapons—the Electric Guitar, Frying Pan, and Golf Club—will be given to players who complete the weekend challenges, while standard blueprints for the weapons will be available as free DLC once the event concludes. It runs until October 27.
It's been longer than you think since Left 4 Dead 2 came out, and if you don't believe me, chew on this: Ten years have passed since Coach, Nick, Rochelle, and Ellis first blazed their way across the Infected wasteland. That's right, a full-on decade—you didn't see that coming, did you? I can barely believe it myself.
Sadly, despite all that time gone by there's still no sign out of Valve that Left 4 Dead 3 is something that will ever actually happen. But it seems like something is happening—in that other first-person zombie game, Dying Light.
Survivors! Are you ready for some serious zombie slaying? #left4dead2 style is coming! pic.twitter.com/Lv4XXyf8JnOctober 23, 2019
Techland actually hinted at this a couple of days ago in a tweet following the end of the Dying Light: Deadeye's Promise event, saying, "We don't want you to be left 4 dead waiting for results!" That got some attention, but a lot of respondents seemed to think it was just a throwaway gag or pre-Halloween reference. Apparently not.
For now, Techland hasn't said anything more about it, and so it falls to us to speculate. It could be (and, I will commit further, probably is) something as simple as Left 4 Dead 2 character skins or cosmetics coming to Dying Light, which the studio continues to actively support despite the fact that it's nearly five years old. But Dying Light 2 is expected to arrive in spring 2020, and so with a little stretching and squinting it's possible to see hope for something more in-depth, especially with Left 4 Dead 2's big 10th anniversary coming in November. (Ten years! Where does the time go?)
I've reached out to Techland and Valve for more information. We'll let you know what happens.