  We present two models for the cosmological UV background light, and calculate
the opacity of GeV gamma--rays out to redshift 9. The contributors to the
background include 2 possible quasar emissivities, and output from
star--forming galaxies as determined by recent a semi--analytic model (SAM) of
structure formation. The SAM used in this work is based upon a hierarchical
build-up of structure in a $\Lambda$CDM universe and is highly successful in
reproducing a variety of observational parameters. Above 1 Rydberg energy,
ionizing radiation is subject to reprocessing by the IGM, which we treat using
our radiative transfer code, CUBA. The two models for quasar emissivity
differing above z = 2.3 are chosen to match the ionization rates observed using
flux decrement analysis and the higher values of the line-of-sight proximity
effect. We also investigate the possibility of a flat star formation rate
density at z $>5$. We conclude that observations of gamma--rays from 10 to 100
GeV by Fermi (GLAST) and the next generation of ground based experiments should
confirm a strongly evolving opacity from $1<$ z $<4$. Observation of
attenuation in the spectra of gamma--ray bursts at higher redshift could
constrain emission of UV radiation at these early times, either from a flat or
increasing star-formation density or an unobserved population of sources.
