Helion, the Sam Altman-backed merger startup, raises $465 million to build a powerhouse for Microsoft

Helion, the 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 money is being pumped in as Helion races to complete its first Orion power plant. The startup has set an aggressive timeline for deploying the power of the fusion in 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. Helion said it has raised $1.5 billion in total.

The new round, 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

Helion’s approach to fusion power differs from many of his peers. Some use magnets to contain the extremely hot plasma required for fusion conditions, while others use lasers to compress the fusion fuel until it reacts. Either way, the majority of startups plan to use steam turbines to convert extreme heat into electricity.

But Helion, which uses magnets to compress fuel, aims 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 drawn from the magnet in the form of electricity, similar to the way an electric car can reverse its motors to provide braking force and recharge the battery.

Such a configuration would significantly improve the efficiency of the fusion power plant. But some fusion experts doubt it can work. This is partly because Helion, unlike many of its competitors, does not frequently publish in peer-reviewed journals, so physicists have not been able to dig into the theoretical underpinnings. Helion CEO David Kirtley says the final results of the company’s fusion devices should be sufficient. “We don’t want to theorize about nuclear fusion,” he told me last year. “We just want to go build it.”

Helion is not alone in attracting new funding. The merger sector has become a darling of investors in recent months. Focused Energy and Thea Energy both announced new rounds last week: Focused for $240 million, and Thea for $100 million. In February, Inertia Energy came out of stealth with a $450 million Series A, and the previous month, Type One Energy said it was raising a $250 million Series B.

Investments have flowed in despite the long merger timeline. Although several companies have made progress in recent months on milestones they say pave the way for a viable power plant, most expect they won’t start operating their first power plant on a commercial scale until the middle of the next decade at the earliest.

Part of the appeal of nuclear fusion is that it can provide almost limitless amounts of continuous energy using only seawater. For technology companies focused on AI, this is an attractive proposition. But it also has the potential to disrupt other trillion-dollar energy markets if fusion energy companies can aggressively cut costs. The timelines may be a little longer than venture capitalists are used to, but the potential payoff can be much greater.