LHC pumps 9000 m^3 to ~10^-9 atm to insulate their cryomagnets. That's the volume of a 2.4 km stretch of the passenger-only hyper-loop, at a million times deeper vacuum. Now, that they're doing that at CERN doesn't mean in any way it's easy or cheap. And the hyper-loop is still a volume a few hundreds of times bigger, without any compartmentalization.
Thermal expansion is also interesting. Back-of-the-envelope:
1.5*10-5 (thermal expansion coef stainless steel) * 40K (guesstimate max delta-T day/night) * 563*10^3m
= 338m thermal expansion/contraction, or 169m at each end.
They'll want to insulate it or at least shield it from direct sunlight -- which the solar panels will partially do.