Turtle Rock Studios has announced that Back 4 Blood‘s first major expansion, Tunnels of Terror, will be released on April 12, while the studio also shared a huge new player number for the game.

So far, more than 10 million people have played Back 4 Blood, and it’s become 2021’s best-selling new IP for consoles, publisher Warner Bros. said. The game hasn’t necessarily sold that many copies, however, as Back 4 Blood is available through Xbox Game Pass. Still, it’s a very big number.

As for the Tunnels of Terror expansion, it’s included with Back 4 Blood’s Ultimate and Deluxe editions, as well as through the Annual Pass. Players can also pick it up by itself, though pricing was not confirmed. The Tunnels of Terror add-on adds the Ridden Hives PvE activity, new playable Cleaners and Ridden, and additional character and weapon cosmetics, among other things.

Ridden Hives has players teaming up to explore seven different dungeons that are overrun with enemies called Warped Ridden. The new Cleaners are called Sharice (and axe-wielding firefighter) and Heng (a “no-nonsense restauranteur”). Additionally, the ultra-difficult No Hope difficulty setting comes to Back 4 Blood alongside Tunnels of Terror, though it will be free and available to everyone.

Additionally, Turtle Rock confirmed that only one player in a party needs to have purchased Tunnels of Terror for everyone to play. The company also said there will be no microtransaction content of any type or shape added to Back 4 Blood in this new expansion.

Concerning the 10 million player milestone for Back 4 Blood, Turtle Rock boss Steve Goldstein said this is a “historic event” for the studio and the game.

Following the launch of Back 4 Blood in 2021, Turtle Rock was acquired by Tencent as part of the Chinese internet behemoth’s continued and growing expansion.