XB-1 is the first independently developed supersonic jet. It is a one-third scale version of 55 passenger jet. If all goes well $6 billion will be raised to build commercial supersonic passenger jets. Boom Aerospace wants the 55 passenger versions to be flying by 2025.
The XB-1 will fly at mach 2.2 by the end of 2019. It is being built now.
Boom Aerospace is using new more efficient engines. Afterburners will not be needed to reach supersonic speed. Materials are lighter and improved. Inlet and other designs are more efficient.