Is it specifically to demonstrate that they can make a quiet aircraft then?
I think I'm curious specifically whether this is more about internal R&D and building systems, or if it's meant to demonstrate they have the capability to to create a performant supersonic aircraft, which they can take to potential investors.
Any idea how often the final design and the prototype don't match in terms of volume and aerodynamics? I would have assumed that those parts are the easiest to model with high confidence.
You don't need to build it to test volume and aerodynamics (math and wind-tunnels can figure that out for you). This is probably more about finding unknown flaws in the design/running down risk. Spending however much on a prototype (10s or 100s of millions of dollars) just to marginally reduce the risk that there's a fundamental flaw in your approach makes a lot of sense when you plan to spend 6 billion total to develop the plane.
I think I'm curious specifically whether this is more about internal R&D and building systems, or if it's meant to demonstrate they have the capability to to create a performant supersonic aircraft, which they can take to potential investors.