Yarr was originally developed for use with Relay (formally Relay Modern) in September 2020 for internal use at Contra. It's since been open-sourced to give back to the community and promote Relay adoption.<p>Yarr is the only routing framework that was built from the ground up with the goal of enabling the render-as-you-fetch concurrent UI pattern. It allows code preloading and data preloading. This behavior is enabled even without opt-in to React's experimental Concurrent Mode.<p>Yarr was primarily architected by Eric Taylor, our super talented engineer, and it captures almost 2 years of our experience working with Relay and evolving render-as-you-fetch pattern. It's already in use in production at <a href="https://contra.com/" rel="nofollow">https://contra.com/</a>