Commonwealth Fusion Systems (CFS) has raised $863 million in a new funding round, attracting investors such as Google, Nvidia, and Breakthrough Energy Ventures. The Massachusetts-based startup has now raised nearly $3 billion, the largest amount of funding for any fusion startup to date.

“This round isn’t just about exploring fusion in principle,” said CEO Bob Mumgaard. “It’s about turning it into an industrially viable technology.” CFS is currently developing Sparc, a prototype reactor that aims to achieve scientific breakeven in 2027, producing more energy than it consumes to initiate the reaction.

Although Sparc will not feed electricity into the grid, it is vital for validating CFS’s designs, cost structures, and operational processes. If successful, the company plans to begin construction of Arc, its commercial-scale fusion plant, in Virginia in 2027 or 2028. A wide base of investors will support both the development of Sparc and the eventual commercialization of fusion power.