TL;DR
For 53 years it has been illegal to fly faster than sound over American soil. That may be about to end. The FAA has proposed swapping the outright ban for a noise cap, and NASA's purpose-built X-59 is already cruising at 1.4 times the speed of sound, about 924 mph, designed to make a soft thump instead of a bang. If the rule lands and the thump is as quiet as promised, jets could legally outrun sound over American towns, judged by how loud they are rather than how fast. The catch: the rule approves no airplane, the one company building a passenger supersonic jet has shifted most of its effort to engines, and nobody has yet measured how the X-59 sounds to the people underneath it.
Below the line, for paid subscribers: The full story: where it stands, how we got here and what's dated next; our Odds board on 6 milestones, starting with "X-59 flies over U.S. communities to survey residents on its thump by 2027"; and every source.