Helion Scores $465M to Build Microsoft’s Fusion Power Plant—Skeptics Want Proof First

Helion, the Sam Altman-backed fusion startup, has raised $465 million in Series G funding, bringing its valuation to $15.5 billion. The company is racing to complete Orion, its first power plant, with a goal of delivering grid-connected fusion power by 2028 under a deal with Microsoft. Total funding now stands at $1.5 billion, following a $425 million round in January 2025.

Thrive Capital led the round, joined by new investors including Alta Park Capital, Lux Capital, and Peak XV Partners, alongside existing backers like Lightspeed Venture Partners, SoftBank Vision Fund 2, and Dustin Moskovitz’s Good Ventures Foundation.

Helion’s technology stands out in the fusion sector. While most startups use steam turbines to convert heat into electricity, Helion plans to capture electricity directly from the magnets that compress its fusion fuel. When the plasma expands during fusion, it pushes against magnetic fields, generating a current—similar to regenerative braking in an electric vehicle. This design could dramatically boost efficiency, but outside physicists remain skeptical. Helion rarely publishes peer-reviewed research, making independent verification difficult. CEO David Kirtley’s response: “We don’t want to theorize about fusion. We just want to go build it.”

The investment comes amid a surge in fusion funding. Focused Energy and Thea Energy each announced rounds last week, while Inertia Energy raised $450 million in February. Despite these bets, most companies don’t expect commercial plants until the mid-2030s. Fusion’s allure for tech giants like Microsoft is clear: near-limitless, always-on energy from seawater. For investors, the timeline may stretch beyond typical VC horizons, but the potential payoff—disrupting trillion-dollar energy markets—is enormous.