Factory Router is an automated model-selection system tailored for autonomous software engineering workflows, aiming to achieve top-tier performance while minimizing costs and enhancing reliability. Rather than relying on engineers to manually identify the optimal model for each task, Factory Router intelligently selects the appropriate model for each Droid session from a varied collection of advanced and efficient models. Routine tasks such as answering simple queries, executing mechanical refactors, making documentation updates, addressing minor bugs, and conducting search-intensive investigations can be efficiently managed by the more streamlined models, whereas complex assignments that require in-depth reasoning can be assigned to the cutting-edge models. Should the chosen model encounter difficulties in completing a task, Factory Router has the capability to transition the session to a more proficient model, ensuring a consistent standard of quality in outcomes. Additionally, it adeptly navigates across different models, providers, and resource capacities whenever issues arise, such as endpoint degradation, rate limits being reached, or limited capacity, thus ensuring uninterrupted operation of Droid sessions. This innovative approach not only enhances productivity but also significantly reduces the burden on engineers, allowing them to focus on more strategic initiatives.