xAI is running its 550,000-GPU Colossus fleet at roughly 11% model FLOPs utilization. An internal memo from infrastructure lead Michael Nicolls confirmed the figure and set a target of 50% — a number that sits at the high end of an industry range where even the best operators, Meta and Google, are only achieving 43–46%. For a company that built the world’s largest AI supercomputer in 122 days, the software stack is still catching up to the hardware.