Designed and built at Lockheed Martin’s Skunk Works facility in Palmdale, California, the Quesst X-plane initially took to the skies on Oct. 28, 2025. That first flight involved low, slow flight for system checks—the aircraft flew for 67 minutes, climbed to an altitude of 12,000 feet, and reached a speed of 230 mph. Since then, the X-59 has reached an altitude of more than 56,000 feet and speeds of up to Mach 1.53.

So it's slower than the X-15 and SR-71 Blackbird, which were built, IIUC, in the 1960s.