<p>Modular architectures could be used to scale quantum devices to the point of fault tolerance and utility. Such modularity is of particular value with superconducting qubits, where monolithically manufactured devices are limited in both system size and quality. However, although prototypical quantum device networks have been fabricated, the development of quantum systems with both interchangeability and high-fidelity operations remains challenging. Here we report a modular architecture for scaling quantum processors with reconfigurable and expandable networks. We develop a high-efficiency interconnect based on a low-loss detachable cable connection between two superconducting qubit devices. We overcome residual loss through a fast pump scheme, enabling intermodule SWAP efficiencies at the 99% level in less than 100 ns. We use the scheme to generate high-fidelity entanglement and operate a distributed logical dual-rail qubit. With an error rate of around 1%, our interdevice operations are at the threshold for fault tolerance.</p>