Horizon Zero Dawn and Death Stranding were developed using Guerrilla Games' Decima engine, which has been in development for over 13 years. Akio Sakamoto, CTO of Kojima Productions, noted that the Decima engine offers many capabilities for building open-world games, despite some features being less user-friendly than those in commercial engines. The collaboration between Kojima Productions and Guerrilla Games, particularly for Horizon Forbidden West, has demonstrated the benefits of custom software in an industry leaning towards widely adopted engines like Unreal. Sakamoto mentioned that they have been using the Decima engine for nearly ten years, highlighting its effectiveness in achieving goals that would be challenging with other engines.