XPP, the X-ray Pump Probe instrument at the Linac Coherent Light Source (LCLS), is back online and welcoming researchers after a complete rebuild. The overhaul has readied XPP for the significant increase in X-ray output expected from the ongoing high-energy upgrade to LCLS at the Department of Energy’s SLAC National Accelerator Laboratory. LCLS is a pioneering X-ray free-electron laser facility used by scientists around the world to capture ultrafast snapshots of natural processes.