In this talk, I will discuss the vector-portal dark matter model, with a dark photon that is slightly heavier than the dark matter. In this regime, a sub-GeV dark matter particle leads naturally to the correct relic abundance, with freezeout controlled by forbidden and 3-to-2 processes. The thermal freezeout behavior of dark matter can be classified into several different phases as a function of dark matter mass and kinetic mixing parameter, with the dark sector temperature evolving in surprising ways within each phase. This model represents an ideal target for upcoming experiments targeting light dark sectors, especially accelerator experiments searching for visibly decaying dark photons. (Based on arXiv:1702.07716, arXiv:2011.01240 and arXiv:2105.05255)