Fusion power startup Commonwealth Fusion Systems has raised $863 million from a long list of investors that includes Nvidia, Google, Breakthrough Energy Ventures, and more. 

“We’re continuing our trend here of looking into the world and saying, ‘How do we advance fusion as fast as possible?’” co-founder and CEO Bob Mumgaard told reporters in a call this week. “This round of capital isn’t just about fusion just generally as a concept, but it’s about how do we go to make fusion into a commercial industrial endeavor.”

The Massachusetts-based company has raised nearly $3 billion to date, the most of any fusion startup. Commonwealth Fusion Systems (CFS) previously raised a $1.8 billion round in 2021.

Fusion power has long been promised as a nearly limitless energy source, though it wasn’t until recently that investors considered it a bet worth placing. As advances in computing and AI have quickened the pace of research and development, the sector has become a hotbed of startup and investor activity.

Inside a fusion reaction, atoms are compressed and heated until they form a fourth state of matter known as plasma. When the plasma reaches the right temperature and pressure, those atoms begin to fuse, releasing tremendous amounts of energy in the process.

CFS is currently building a prototype reactor called Sparc in a Boston suburb. The company expects to turn that device on later next year and achieve scientific breakeven in 2027, a milestone in which the fusion reaction produces more energy than was required to ignite it. 

Though Sparc isn’t designed to sell power to the grid, it’s still vital to CFS’s success.

“There are parts of the modeling and the physics that we don’t yet understand,” Saskia Mordijck, an associate professor of physics at the College of William and Mary, told TechCrunch. “It’s always an open question when you turn on a completely new device that it might go into plasma regimes we’ve never been into, that maybe we uncover things that we just did not expect.”

Assuming Sparc doesn’t reveal any major problems, CFS expects to begin construction on Arc, its commercial-scale power plant, in Virginia starting in 2027 or 2028.

The Sparc and Arc designs are both tokamaks, a type of fusion reactor that uses powerful superconducting magnets to confine and compress plasma. Tokamaks are well known among the research community.

“We know that this kind of idea should work,” Mordijck said. “The question is naturally, how will it perform?”

Investors appear to like what they’ve seen so far. The list of participants in the Series B2 round is lengthy. No single investor led the round, and a number of existing investors increased their stakes, said Ally Yost, CFS’s senior vice president of corporate development. 

Existing investors that increased their stakes include Breakthrough Energy Ventures, Emerson Collective, Eni, Future Ventures, Gates Frontier, Google, Hostplus, Khosla Ventures, Lowercarbon Capital, Safar Partners, Eric Schmidt, Starlight Ventures, and Tiger Global.

The new investors include Brevan Howard, Morgan Stanley’s Counterpoint Global, Stanley Druckenmiller, FFA Private Bank in Dubai, Galaxy Interactive, Gigascale Capital, HOF Capital, Neva SGR, Nvidia’s NVentures, Planet First Partners, Woori Venture Partners US, and a consortium of 12 Japanese companies led by Mitsui & Co., Ltd. and Mitsubishi Corporation.

Such a broad base of investors may prove helpful as the company develops its supply chain and searches for partners to build its power plants and buy electricity from them. So far, the company has inked a deal with Google to buy 200 megawatts from Arc.

As the first of its kind, Arc is likely to cost more than subsequent power plants, Mordijck said.

And while Sparc will help prove the science is sound, it will do more than that for CFS, Mumgaard told TechCrunch. “That’s very important. But it’s also to know the capabilities that you need to be able to deliver it. It’s also to have the receipts, know what these things cost.”

The new round will help CFS make progress on Sparc, but it will not be enough to build Arc, which will likely cost several billion dollars, Mumgaard said. At this point, the company doesn’t know exactly what shape the funding for Arc will take.

“The fact that it’s a first of a kind technology is a wrinkle that then has a big impact on where the capital will come from,” he said. “We’re not entirely sure, but we are pretty committed to doing this. And our investors are pretty committed to doing this.”