The Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory is undergoing a major upgrade, LCLS-II-HE, to increase its X-ray energy 3,000-fold. This upgrade will enable scientists to explore atomic-scale processes in various fields. Funded by the DOE, LCLS was the first to produce high-energy X-rays with a free-electron laser. The 2023 upgrade added a superconducting accelerator and undulators, producing a million X-ray pulses per second. LCLS-II-HE will double the electron beam energy with 23 new cryomodules, enhancing performance. Installation is planned for 2026.