We are very excited to announce a major new release of ILLIXR (ILLinois eXtended Reality testbed) - a significant milestone towards our grand challenge goal of comfortable, mobile, all day, rich immersive experiences. The stringent power budgets of mobile and lightweight XR devices imply that not all immersive computations can be performed locally — remote offloading or Distributed XR is essential. ILLIXR v4.0 is the first open-source end-to-end XR system that supports offloading of both head tracking and rendering (with 6DoF reprojection in the runtime), either separately or together. This release also introduces several other major upgrades, including hand tracking, plugin support for ORB_SLAM3 integration, and a new network backend that enables the offloading of multiple components under the coordination of the runtime.