RouterArena is an open platform designed to evaluate the performance and efficiency of model routers, which are becoming crucial as the landscape of large language models (LLMs) diversifies from general-purpose giants to more specialized and efficient models. As LLMs expand in variety, selecting the most suitable model for a given task has become a complex challenge, akin to how Google Search routes queries to relevant sources. RouterArena addresses this by providing a comprehensive dataset and a framework for assessing routers across five key metrics: query-answer accuracy, cost efficiency, routing optimality, robustness, and latency. The platform hosts a public leaderboard that allows the community to compare and improve routers, fostering a shift from the "one-model-for-all" approach to a more nuanced ecosystem where intelligent model routing is essential. As the demand for more personalized and efficient AI systems grows, RouterArena aims to standardize and simplify the evaluation process, encouraging innovation in router design and functionality.