This article considers user participation in 3D development practices, known as mod development, in the commercial setting of the 3D software industry. By drawing on two prominent developer firms, i.e. Valve Inc. and Linden Lab, this article is designed to learn more about the increasing importance attributed to user participation in this context by exploring the ways in which these software developer firms facilitate or invite users to participate in development practices. The results of interviews conducted with employees of these firms, and an online survey with their respective user base, are used as evidence. The article demonstrates that, to various extents, interdependencies develop between the firm, users and technologies, directing our attention to the boundaries of participation and competition. It extends our understanding of how certain participatory designs provide a structure to how game development is informed and organized across firm boundaries based on the moderating role of product and user characteristics.