In a media briefing, Mumgaard noted that this latest raise marks “the largest single funding round among fusion energy companies since our last large round of $1.8 billion in 2021.” It brings the total capital raised by CFS to an even $4 billion as the company races to complete construction of SPARC, its demo reactor. If all goes according to plan, it should begin operating sometime next year, proving out the physics and engineering approach underpinning ARC, the planned commercial plant.
The new financing deviates from the typical venture capital round, as it brings in a broad but unnamed mix of “large pension funds, sovereign wealth funds, infrastructure funds doing project finance, and industrial corporates.” These risk-averse investors would typically steer clear of expensive, first-of-a-kind facilities, demonstrating the degree to which CFS has succeeded in building confidence in an industry long critiqued for overpromising and underdelivering.
The company credits the trust it built to its extensive peer-reviewed research as well as its decision to build a tokamak — widely regarded as the most mature fusion reactor design. “I don’t think there’s any other company that’s been as transparent and open with their physics and how it actually works,” Katie Rae, CEO and managing partner at Engine Ventures, told me. Rae has participated in every one of CFS’s funding rounds, and while she says her firm has evaluated virtually every startup in the sector, the company remains its only fusion investment.
But even flush with institutional capital, Mumgaard is clear that the company will need billions more to fully finance ARC and the numerous reactors to follow. It’s unclear where exactly that money will come from, though he’s pushing for government involvement. Alongside the Fusion Industry Association, Mumgaard is advocating for a one-time, roughly $10 billion federal infusion of cash into the broader industry to expand public-private partnerships, build shared research infrastructure, and help finance first-of-a-kind plants in an effort to keep pace with China’s rapidly growing fusion program.
According to reporting from Politico, a Department of Energy official told CFS and other fusion companies that such a level of federal funding is “unrealistic in this environment.” But though insiders argue it’s what the industry needs to scale, Rae says CFS doesn’t depend on it. “I think it is the right kind of investment to make, but we didn’t count on it from an investor perspective,” she told me.
One obvious alternative is the public markets. The IPO window for climate tech has reopened, with geothermal giant Fervo and nuclear fission startup X-energy both completing successful public offerings in recent months. SPACs have also made a comeback, as numerous nuclear companies are opting for this faster, though riskier, path to the public markets. But CFS’s newly appointed CFO, Lorence Kim, said during the briefing that this latest round proves “that the private markets have a lot of capital to deploy toward our mission.” Whether an IPO is in the company’s near future remains an open question, though he cautioned against interpreting his hiring as any indication of “IPO prep in a specific way.”
For what it’s worth though, Kim has taken another high-profile, pre-revenue startup public before: Moderna. As CFO from 2014 to 2020, he helped the company scale its mRNA platform and lead its blockbuster $600 million IPO in late 2018 — the largest ever in the biotech industry at the time. Notably, this all happened before Moderna had an approved product or the Covid pandemic made its signature vaccine a household name, similar to where Commonwealth finds itself today.
“Moderna was in this moment in time where the science worked, and the strategy was focused on execution and scale and deploying capital in a way that could enable real impact on the world,” Kim explained. CFS is now at the same juncture, he said. “And so in the same way that Moderna industrialized mRNA and made it inevitable and made it ubiquitous, it was really clear to me that CFS could do the same for fusion.”
Of course, CFS is not alone in its confidence — other fusion companies are equally bullish on their own approach. Take Inertia Enterprises, a Lawrence Livermore National Laboratory spinout, which last week unveiled its own commercial roadmap for a laser-driven fusion reactor. The company emphasized it’s the only one to have definitively demonstrated the viability of its underlying physics in a real-world experiment, rather than through theoretical work or simulations.
Or take Helion, which has raised $1.5 billion and secured a highly ambitious power purchase agreement with Microsoft to supply electricity to the tech giant by 2028. Or Pacific Fusion, which netted a staggering $900 million Series A to be doled out in milestone-based tranches. There are dozens of others — many with hundreds of millions in funding — pursuing a range of approaches that some of the field’s brightest minds consider technically feasible.
But when I mused to Rae about how exciting it is that institutional investors now appear willing to back an industry once viewed as bordering on science fiction, she was quick to correct me.
“They’re willing to bet on Commonwealth Fusion — that’s what you mean.”
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A Permian Basin methane plume.Carbon Mapper 
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A transformer factory in Jiangsu Province, China. Costfoto/NurPhoto via Getty Images
