  The current framework for dark matter searches at beam dump and fixed target
experiments relies on four benchmark models, the complex scalar, inelastic
scalar, pseudo-Dirac and finally, Majorana DM models. While this approach has
so far been successful in the interpretation of the available data, it a priori
excludes the possibility that DM is made of spin-1 particles -- a restriction
which is neither theoretically nor experimentally justified. In this work we
extend the current landscape of sub-GeV DM models to a set of models for spin-1
DM, including a family of simplified models (involving one DM candidate and one
mediator -- the dark photon) and an ultraviolet complete model based on a
non-abelian gauge group where DM is a spin-1 Strongly Interacting Massive
Particle. For each of these models, we calculate the DM relic density, the
expected number of signal events at beam dump experiments, the rate of energy
injection in the early universe thermal bath and in the Intergalactic Medium,
as well as the helicity amplitudes for forward processes subject to the unitary
bound. We then compare these predictions with experimental results from Planck,
CMB surveys, IGM temperature observations, LSND, MiniBooNE, NA64, and BaBar and
with available projections from LDMX and Belle II. Through this comparison, we
identify the regions in the parameter space of the models considered in this
work where DM is simultaneously thermally produced, compatible with present
observations, and within reach at Belle II and LDMX. We find that the
simplified models are strongly constrained by current beam dump experiments and
the unitarity bound, and will thus be conclusively probed in the first stage of
LDMX data taking. We also find that the SIMP model explored in this work
predicts the observed DM abundance, is compatible with current observations and
within reach at LDMX in a wide region of the parameter space.
