  I present theoretical calculations of $t{\bar t}$ production cross sections
through aN$^3$LO in proton-proton collisions. I show that soft-gluon
corrections dominate the perturbative expansion not only for LHC energies but
also for future collider energies through 100 TeV. Detailed results are
presented for various collision energies. The $K$-factors are large and
increase slowly with increasing energy. The scale uncertainties decrease
greatly as we move to higher perturbative orders.
