Commonwealth Fusion Systems has raised a further $1 billion, reinforcing its position as the most heavily funded fusion-energy start-up. The funding will support efforts to commercialise fusion power as the company builds its Sparc demonstration reactor and completes designs for its first commercial plant, Arc; however, the technology has yet to prove it can supply electricity to the grid.

CFS has now raised $4 billion in total, with the latest round involving institutional investors including pension funds, sovereign wealth funds and industrial partners, though it did not identify them. Sparc is expected to reach scientific breakeven in 2027, meaning its fusion reactions would produce more energy than is needed to initiate them, while Arc is planned for Virginia with 400 megawatts of output; Eni has agreed to buy over $1 billion of its electricity and Google has committed to 200 megawatts.