Commonwealth Fusion Systems (CFS), a Massachusetts-based startup focused on fusion energy, has raised $863 million in its Series B2 funding round. Leading investors include Google, Nvidia, Breakthrough Energy Ventures, and a consortium of global partners.

CEO Bob Mumgaard stated, “We’re looking at fusion not only as science but as a path to commercial energy production.” With nearly $3 billion raised to date, CFS is the most well-funded startup in the fusion sector.

CFS is building Sparc, a tokamak prototype that will begin operation next year. The reactor aims for scientific breakeven in 2027, generating more energy than it consumes to initiate the fusion reaction. While Sparc won’t supply the grid, it is crucial for testing technology, measuring costs, and preparing for Arc, CFS’s planned commercial fusion plant in Virginia starting in 2027–2028.

Investors hope that such a broad funding base will enable CFS to secure supply chains, build partnerships, and pave the way toward industrial-scale fusion energy.