Heliumthe Sam Altman-backed fusion startup announced Thursday that it has raised $465 million in a new funding round that values the company at $15.5 billion.
The cash injection comes as Helion struggles to complete Orion, its first power plant. The startup has set an aggressive timeline for deploying fusion power on the network as early as 2028 if it can meet the terms of its deal with Microsoft.
The startup last raised $425 million in January 2025. In total, Helion said it has raised $1.5 billion.
The new round, a Series G, was led by Thrive Capital with a long list of participants including new investors Alta Park Capital, Anti Fund, BoxGroup, Lux Capital, Peak XV Partners and Bill Ford, along with existing investors including Capricorn Technology Impact Funds, Lightspeed Venture Partners, Mithril Venture Capital, Mithril Venture Capital, Fund 2, and a university endowment fund.
Helion’s approach to fusion power differs from many of its peers. Some use magnets to contain the superheated plasma required for fusion conditions, while others use lasers to compress the fusion fuel until it reacts. In both cases, the majority of startups plan to use steam turbines to convert intense heat into electricity.
But Helion, which uses magnets to compress the fuel, plans to harvest electricity directly from the magnets themselves. When fusion occurs in the plasma inside the reactor, it expands, pushing against the magnetic fields. This force can be extracted from the magnets as electricity, similar to how an electric vehicle can reverse its motors to provide braking force and recharge the battery.
Such a configuration would dramatically improve the efficiency of a fusion power plant. But some fusion experts are skeptical it could work. That’s partly because Helion, unlike many of its competitors, doesn’t often publish in peer-reviewed journals, so physicists haven’t been able to look at the theoretical underpinnings. David Kirtley, CEO of Helion, argues that the final results from the company’s fusion devices should be sufficient. “We don’t want to theorize about fusion,” he told me last year. “We just want to go fix it.”
Helion is not alone in attracting new funding. The fusion sector has become an investor favorite in recent months. Focused Energy and Thea Energy both announced new rounds last week: Focused for $240 million, Thea for $100 million. In February, Inertia Energy came out of stealth with a $450 million Series A, and last month, Type One Energy said it was in the process of raising $250 million for a Series B.
Investments have poured in despite fusion’s long timeline. Although several companies have made progress in recent months on milestones they say pave the way for a sustainable power plant, most predict they won’t start operating the first commercial-scale power plant until the middle of the next decade at the earliest.
Part of the appeal is fusion’s ability to provide nearly limitless amounts of always-on energy using little more than seawater. For tech companies focused on artificial intelligence, this is an attractive proposition. But it also has the potential to disrupt other trillion-dollar energy markets if fusion power companies can aggressively drive down costs. The timelines may be a bit longer than VCs are used to, but the potential payoff could be much greater.
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