CORSIKA 8 is a modern, flexible framework for simulating particle cascades in air and dense media, allowing for fully customizable shower simulations. The radio module autonomously handles electric field calculations and propagation to observer locations. It supports simultaneous simulations with both the "Endpoint formalism" as implemented in CoREAS and the "ZHS" algorithm from ZHAireS. In this contribution, we validate the radio module by comparing air-shower simulations in CORSIKA 8, CORSIKA 7, and ZHAireS. We investigate the impact of simulation parameters, such as the step size of particle tracks, on the resulting radio signals and perform a detailed comparison of the "Endpoints" and "ZHS" formalisms. For the same underlying showers simulated with CORSIKA 8 with optimized step sizes, both formalisms converge to the same radiation energy within 2%. For CORSIKA 8 and CORSIKA 7, agreement on the radiation energy is better than 10% in the 30–80 MHz band and improves to better than 2% for 50–350 MHz. This consistency provides further confirmation of the accuracy of microscopic air-shower radio emission simulations which is crucial for precise energy scale estimations using radio detection.