Helion, Backed by Sam Altman, Raises $465M to Build a Power Plant for Microsoft

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Helion, the fusion startup backed by Sam Altman, announced on Thursday that it had raised $465 million in a new funding round that values the company at $15.5 billion. This significant investment comes as Helion is racing to complete Orion, its first power plant, with an aggressive timeline to deploy fusion power to the grid as early as 2028. The startup's approach to fusion power differs from many of its peers.

While some use magnets to contain the superheated plasma required for fusion conditions, and others use lasers to compress fusion fuel until it reacts, Helion uses magnets to compress the fuel. The company intends to harvest electricity straight from the magnets themselves, a configuration that would dramatically improve the efficiency of a fusion power plant. However, some fusion experts are skeptical about Helion's approach, citing the lack of peer-reviewed publications on the company's theoretical underpinnings.

Helion's CEO, David Kirtley, argues that eventual 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 build it." This 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.

Helion has now raised a total of $1.5 billion, following its previous raise of $425 million in January 2025. The fusion sector has become an investor darling in recent months, with several companies announcing new funding rounds. Focused Energy and Thea Energy both announced new rounds last week, and Inertia Energy emerged from stealth with a $450 million Series A in February.

Despite fusion's lengthy timeline, investors are attracted to its potential to deliver nearly limitless amounts of always-on energy using little more than seawater. The investments have poured in despite the fact that most fusion companies predict they won't begin operating their first commercial-scale power plant until the middle of the next decade at the earliest. However, the potential payoff could be a lot bigger, with the possibility of disrupting other trillion-dollar energy markets if fusion power companies can aggressively drive costs down.