The Mach 4 Quiet Ludwieg Tube (QLT4) has been successfully installed as the first operational tunnel of the Boundary Layer Stability and Transition (BLST) experimental facility at the University of Arizona. Results from an initial flow-quality and performance assessment campaign are reported. QLT4 produces Mach 4 flow that is stable across a range of operating conditions to within 1.5% of the nominal free-stream value. The tunnel is capable of producing quiet flow up to a total pressure of pt1 = 95.4 kPa (13.8 psia) and a unit Reynolds number of 4.27 × 106 m−1 near the downstream end of the quiet core as reported by Schneider and Haven . Maximum quiet pressure is observed to decrease as the probe approaches the tunnel walls and as the probe moves downstream.