Dead Island developer Techland’s open-world zombie game Dying Light has now reached 4.5 million unique users, up from 3.2 million back in March. This number isn’t the same as sales, however.

Actual sales are “slightly less,” Techland CEO Pawel Marchewka told Eurogamer.

“Sales [we] count later–we need time to calculate the sales and returns and so on. Unique users means all the unique users we calculated on the server playing the game for significant number of time,” he added. “Sales might be slightly less because that includes also secondary sales.”

Techland has supported Dying Light with a few pieces of DLC so far, but is a full-blown expansion in the works? “We are thinking about maybe something really of bigger scope,” Marchewka teased. Asked if he was referring to an expansion, he said with a smile, “I don’t know if I can say that. We’ll see, we don’t know that yet.”

Marchewka also suggested that plans are underway for Dying Light 2.

“Obviously, we’re also thinking about how to think about the sequel, what should happen there,” he said. “So a lot of talk going on right now.”

Also in the interview, Marchewka said Techland’s focus on the Dying Light series is why the studio made the decision to put its co-op action game Hellraid on hold. This game is definitely not canceled, however.

“Dying Light–every one of our games–had this problem,” Marchewka said. “We always wanted to create something bigger than we should. Then we cut it in half and still it’s bigger than it should [be]!”

“It’s definitely not dead,” he added. “It’s just we want to make sure the needs from our Dying Light players are satisfied as quickly as possible and we needed some resources for that.”