COMMONWEALTH FUSION SYSTEMS

CFS spun out of MIT's Plasma Science and Fusion Center in 2018. The breakthrough was a new type of high-temperature superconducting (HTS) magnet made with a material called REBCO tape.

Stronger magnets mean you can build smaller, cheaper fusion reactors. Previous fusion attempts (like ITER, the $25 billion international project in France) used old magnet technology that required building a reactor the size of a building.

CFS's magnets allow a reactor the size of a tennis court. In September 2021, they successfully demonstrated a 20-tesla HTS magnet — the most powerful of its kind ever built.

CFS doesn't have revenue yet — they're in the R&D and reactor construction phase. The future business model is: build compact fusion power plants (called ARC) and sell the electricity, or license the technology to utilities and governments.

Each ARC reactor would produce about 400 MW of clean, continuous electricity — enough to power roughly 400,000 homes. The fuel is deuterium (from water) and tritium (bred from lithium) — both effectively unlimited.

Zero carbon emissions, no meltdown risk, minimal radioactive waste.

SPARC (compact fusion demonstration reactor, under construction), High-temperature superconducting (HTS) magnets, ARC (planned commercial fusion power plant), REBCO tape magnet technology.

CFS's roadmap is: build SPARC, prove net energy gain, build ARC, then license and deploy globally. SPARC is under construction in Devens, Massachusetts, is scheduled to start operating in 2026, and aims to demonstrate net power in the first quarter of 2027.

ARC, the first commercial plant, is going up in Chesterfield County, Virginia, with Dominion Energy as the site partner and Google already contracted to buy half its output. CFS expects to connect it to the grid in the early 2030s.

If SPARC succeeds, CFS becomes the most important energy company in the world overnight. The magnet technology is already being explored for other applications, including MRI machines, particle accelerators, and industrial processes.

Making fusion actually work as a net energy source. No fusion device on Earth has ever produced more energy than it consumed in a sustained, controlled way.

SPARC, under construction in Devens and due to start operating in 2026, aims to be the first, with net power targeted for the first quarter of 2027. The physics says it should work, and MIT's simulations and the magnet tests are promising, but the engineering challenges are immense.

Plasma at 100 million degrees Celsius is not easy to contain. Burn rate is also brutal.

CFS has raised close to $3 billion and still has not sold a single electron.

Bill Gates (Breakthrough Energy Ventures), Google, Nvidia's venture arm NVentures, Salesforce founder Marc Benioff, Tiger Global, Temasek, Khosla Ventures, DFJ Growth, The Engine (MIT), Emerson Collective, and the Italian energy company Eni. The $863 million Series B2 in September 2025 was the largest round raised by any deep tech or energy company since CFS's own $1.8 billion Series B in 2021.

All in, CFS has raised close to $3 billion, roughly a third of every dollar ever put into private fusion.