  Several proposals exist for energy-frontier facilities after the HL-LHC. In
this contribution I review the potential of these facilities to perform key
measurements of top quark properties and interacions. Top quark precision
physics at a lepton collider provides excellent opportunities for the
determination of the top quark mass and its couplings to neutral electro-weak
gauge bosons. Measurements at very high center-of-mass energy at a new hadron
collider likely offer the ultimate precision on the QCD interaction of the top
quark and its coupling to the Higgs boson. The combination of a lepton and a
hadron collider can improve the precision of all these measurements by two
orders of magnitude with respect to the current state-of-the-art and by an
order of magnitude compared to the precision envisaged after 3/ab at the LHC.
