Quench detection and protection in REBa₂Cu₃O_7−δ (REBCO) coated conductor (CC)-based superconducting magnets is difficult due to slow normal zone propagation velocity and the multilayer composite architecture of the conductor. To design effective quench detection and protection methods, it is essential to know the electrical, thermal, and structural behavior during the quench at multiple length scales ranging from the micrometer scale within the layers of the conductor to the macroscopic behavior of the coil. Here, a hierarchical multiscale approach is used to develop a modular 3-D electro–magneto–thermal coil quench model. The model uses an accurate experimentally validated micrometer-scale REBCO CC model as the basic building block. The model is embedded within a homogenized coil framework at one or more locations in the form of multilayer tape modules. This multiscale approach makes possible the studies of quench behavior at the micrometer scale within a tape at any location of interest within a coil without requiring a computationally extensive model of the entire coil. This approach also enables the building of more complicated models by hierarchically integrating smaller modular blocks with the same repeatable modeling techniques. Here, the development of the electro–magneto–thermal coil quench model is first presented, followed by its experimental validation. Simulation results and their implications for coil reliability and quench detection and protection are then discussed