Abstract: This talk analyzes the present status of sub-GeV thermal dark matter annihilating through Standard Model mixing. In these scenarios, the requirement that dark matter be a thermal relic sets a sharp sensitivity target for terrestrial experiments, and that one of the simplest and best-motivated interactions between the SM and light dark matter (the vector portal) remains viable. Moreover, it is demonstrated that a small set of future experiments can decisively test these models. In particular, the future LDMX experiment can play a key role in most of the remaining parameter space in simple models.