The F-35 is also low-observable. I'm a total lay-person on this one, but I'm betting that the tolerances for achieving flight (even at Mach 2.2) are a lot looser than the tolerances for being invisible.
Yeah, the F-35 is actually milled down during/after assembly for low observables. However, the Mig-21 can hit the same speeds as the XB-1 and it has panel gaps visible from several meters.
I did some reading and the XB-1 does use hydraulics. From VEP and other companies.
It looks like they will be using titanium leading edges to handle the heat loads.
They are using a J85-GE-15. I don't think that will allow them to reach M2.2. Closer to M1.7 or so? Depends on the inlets I think.
(I was wrong on the engines. They are using 3x engines, not the 2x afterburning that I was expecting. So the speed looks reasonable)
