If dark energy evolves in time its dynamical component could be dominated by a bath of dark radiation. Since dark energy was subdominant in the early universe, the dark energy radiation evades the usual stringent constraints on extra relativistic species from the cosmic microwave background, allowing for three percent of the energy density today to be dark radiation. In this talk, I will discuss how dark energy radiation can emerge from a fundamental theory, its predictions for cosmological observables, as well as discovery potential and constraints with existing and future precision cosmological datasets including measurements of the cosmic microwave background, baryon acoustic oscillations, and supernova data. Considering extensions that allow the dark radiation to populate neutrinos, axions, and dark photons, I will discuss the direct detection prospects of a thermal background comprised of these candidates consistent with cosmological constraints on dark energy radiation. A resolution of 6 meV is required to achieve sensitivity to relativistic neutrinos compatible with dark energy radiation in a neutrino capture experiment on tritium. Dark matter axion experiments lack sensitivity to a relativistic thermal axion background, even if enhanced by dark energy radiation, and dedicated search strategies are required to probe new parameter space. However, several orders of magnitude of viable parameter space can be explored for a relativistic dark photon background sourced by dark energy radiation with planned experimental programs such as DM Radio and LADERA.