  GeV-scale dark matter is an increasingly attractive target for direct
detection, indirect detection, and collider searches. Especially for masses in
the MeV to GeV range, indirect detection is expected to give a leading
constraint. In that range, dark matter annihilations into hadronic final states
produce a challenging zoo of light hadronic resonances. With an update of
Herwig7, we provide a modeling of these processes and study energy spectra from
annihilation through a vector mediator. We cover dark matter masses between 250
MeV and 5 GeV and include an error estimate. This opens up new opportunities
for fully studying indirect detection signals for hidden dark matter sectors
with vector mediators in the sub-GeV range.
