The development of Stalker 2's version 2.0 update, which accompanied the launch of its Cost of Hope expansion, involved a challenging engine overhaul. GSC Game World's COO and head of creative, Maria Grygorovych, described the process of updating the game's engine from Unreal Engine 5.1 to 5.5.4 as a "nightmare," though ultimately worthwhile.
This extensive engine update proved particularly complex for Stalker 2 due to the team's highly customized implementation of Unreal Engine 5.1. "We had so much of our own code. It cost an enormous amount of time," Grygorovych stated in an interview with PC Gamer. "If you work closer to the vanilla version, it's much easier."
CEO and head of game direction Ievgen Grygorovych elaborated that the transition was further complicated by the game's development history. The project initially began on Unreal Engine 4 before moving to an early version of Unreal Engine 5. At the time, the available open-world features in Unreal Engine 5 were not compatible with the scale of Stalker 2, necessitating significant custom modifications. When newer versions of Unreal Engine introduced Epic's own systems to handle these functionalities, GSC was required to re-integrate their custom code. "For us, it took much more time and effort than it might for other projects," he explained.
Despite the difficulties, the engine upgrade brought benefits to earlier versions of the game as well. Ievgen Grygorovych noted that the process allowed the team to identify and backport optimizations, which were released in Stalker 2's version 1.7. "Most of that was delivered because of things we backported while we were [working on the engine update]," he said. "We could've waited until we transitioned to the new engine, but it would've taken a long time. Or we could backport it, test it, and give those optimizations much earlier."
The developers expressed no regret in moving away from the proprietary X-Ray engine used in previous Stalker titles. "We need a lot of engineers, and it's impossible to find like 60 engineers who have experience working with X-Ray," Ievgen Grygorovych stated. "It's much more possible to find 60 engineers who know how to work with Unreal." Maria Grygorovych added that adopting a standardized engine like Unreal also benefits the career prospects of GSC's developers, making them more employable in the broader industry.
"It's a lot of pros and cons with [a standardized engine like Unreal]. It's not a matter of right decision or wrong decision," she concluded. "Each company needs to decide for themselves. This was the best solution for us." Ievgen Grygorovych summarized the decision by stating, "The engine is a tool. You're choosing the right tool for the right project."