  We present calculations of the time evolution of the prompt spectra of
gamma-ray burst models involving generic internal dissipation regions,
including internal shocks, either by itself or in the presence of an external
photon source such as a photosphere. The method uses a newly developed
time-dependent code involving synchrotron emission and absorption, inverse
Compton scattering and pair formation. The models reproduce the typical
observed Band spectra and their generic time evolution, including the
appearance of an extra keV-GeV component, whose delay in simple SSC models,
however, is only partially able to explain the several seconds observed GeV
delays. On the other hand, models involving both a photosphere and an internal
dissipation region at a larger radius produce both an extra GeV component and
time delays which are in the range of the observations.
