  We calculate the GeV spectra of GRB afterglows produced by inverse Compton
scattering of the sub-MeV emission of these objects. We improve on earlier
treatments by using refined afterglow parameters and new model developments
motivated by recent Swift observations. We present time-dependent GeV spectra
for standard, constant parameter models, as well as for models with energy
injection and with time-varying parameters, for a range of burst parameters. We
evaluate the limiting redshift to which such afterglows can be detected by the
GLAST LAT, as well as AGILE.
