A new expansion for "Horizon: Zero Dawn" is in the works.

"Horizon Zero Dawn" has indeed proven a major success for Sony with the impressive sales of PlayStation 4 (PS4) and mostly positive reviews of the console from both critics and fans. According to reports, Guerilla Games has confirmed that the first downloadable content (DLC) for the hit game is now in development.

When pressed for further details, the studio politely refused to shed light on the matter. However, Guerrilla's Managing Director Hermen Hulst assured fans that they are "already hard at work" on the update and it will be an exciting expansion to lead character Aloy's story.

The DLC announcement comes after the game reached a new milestone with more than 2.5 million copies sold worldwide. The staggering sales were recorded just two weeks after its Feb. 28 release. Aside from being the studio's biggest debut title ever, the action role-playing game is now listed as the best-selling new first-party intellectual property (IP) launch on the PS4 system.

"We knew 'Horizon Zero Dawn' was going to be something special, so to see the incredible critical reaction to a brand new game world translate into this level of sales is really gratifying," said Chairman of SIE Worldwide Studios Shawn Layden in a press release.

In other news, fans can now get a glimpse of the evolution of Aloy's character model through a new art book. Titan Books has published "The Art of Horizon Zero Dawn," a 192-page hardcover book that features hundreds of never-before-seen illustrations, concept arts, and other photos from the game. It also includes insights into the development process from the developers. The book is written by Paul Davies and it can now be purchased on Amazon for $24.66.

"Horizon Zero Dawn" centers on a skilled female hunter named Aloy, who navigates a lush and vibrant world populated by strange mechanized creatures. The game is exclusive to PS4 consoles.