American fusion energy company developing compact HTS tokamak reactors. Commonwealth Fusion Systems (CFS) is a private fusion energy company based in Devens, Massachusetts. Founded in 2018 as a spin-off from MIT’s Plasma Science and Fusion Center, CFS aims to commercialize fusion power using cutting-edge high-temperature superconducting (HTS) magnet technology. Their VIPER magnets enable compact tokamak reactors, with the company’s flagship SPARC project pursuing the world’s first net-energy fusion. Following SPARC, CFS intends to develop the ARC commercial power plant, targeting the delivery of hundreds of megawatts of electricity by the early 2030s. CFS has become a leader among private fusion ventures, raising several billion dollars in funding, and in 2025 announced pioneering agreements for fusion offtake with major corporations such as Google. The company employs approximately 1,000 people and continues to expand as it works toward realizing practical fusion energy.