Tunnels of Terror is included as part of the Ultimate Edition, Deluxe Edition and Annual Pass for Back 4 Blood, while players who bought the standard edition of the game will be able to buy it separately.
The expansion includes a new PvE co-operative activity called Ridden Hives, as well as new playable Cleaners and Ridden variants.
The news coincides with publisher Warner Bros Games’ announcement that the game has been played by over 10 million players since its release in October.
Back 4 Blood - campaign trailer
Tunnels of Terror’s new Ridden Hives mode will see teams of up to four players exploring “seven different dungeons full of labyrinthine tunnels below the depths of Evansburgh that are infested with a new Ridden type, Warped Ridden,” according to Turtle Rock.
“To claim exclusive loot and rewards only offered in Ridden Hives, players must outmanoeuvre and overcome the daunting new Warped Ridden, including the landmine-setting Urchins, monstrous Shredders, and damage-dealing Rippers.”
The DLC also includes two new playable characters – Sharice, who’s a firefighter with an axe, and Heng, who’s a “tough as nails, no-nonsense restaurateur”.
Also included in the expansion are eight new character skins, seven new legendary weapons, 12 new weapon skins and new cards.
According to Turtle Rock, as long as at least one player in a party has purchased the Tunnels of Terror expansion, all players in that party will have access to its playable content.
There will also be a free update released at the same time which includes a new No Hope difficulty setting.
Back 4 Blood previously received a free update in December which added a single-player campaign mode. Before the update, VGC’s Back 4 Blood review had criticised the game’s single-player element, calling it “pointless” and “incomplete”.