Helion Hits a $15.5 Billion Valuation as Sam Altman's Fusion Bet Races to Power Microsoft by 2028

Helion Energy, the fusion startup backed by OpenAI chief executive Sam Altman, raised a $465 million Series G at a $15.5 billion valuation, announced June 4, 2026. The round nearly triples the company’s valuation in 17 months and pours extraordinary capital into one of the boldest — and most doubted — promises in clean energy: delivering commercial fusion power to the grid by 2028.

The round and the numbers

The financing was led by Thrive Capital, with new investors including Alta Park Capital, Anti Fund, BoxGroup, Lux Capital, Peak XV Partners and the investor Bill Ford. It marks a steep step up from Helion’s prior $5.43 billion valuation, set in January 2025, and brings the company’s total funding to roughly $1.5 billion.

The cash has a specific purpose: to complete Orion, Helion’s first power plant.

What Helion is building

Fusion — the reaction that powers the sun — has been “30 years away” for decades. Helion’s approach differs from the giant tokamak reactors pursued by much of the field. It uses a pulsed, magneto-inertial design intended to convert fusion energy directly into electricity, which the company argues is a faster, cheaper path to commercialization. Orion, under construction in Washington state, is meant to prove it.

The Microsoft deal and the 2028 clock

What makes Helion unusual is that it has already promised to sell the electricity. Under a deal first struck in 2023, Helion agreed to supply Microsoft with fusion power for a data center in central Washington as early as 2028. That deadline is the defining feature — and the defining risk — of the entire enterprise. Most physicists regard a 2028 commercial-fusion target as wildly optimistic, and the penalty terms if Helion misses are not public.

The Altman web

The financing sits at the center of an increasingly tangled set of relationships in the AI and energy worlds. Altman is Helion’s most prominent backer, and reporting indicates Helion has also explored selling power to OpenAI, separate from the Microsoft arrangement. The optics are pointed: the same figures driving the AI boom — whose data centers consume staggering amounts of electricity — are funding the power sources meant to feed it. Critics see a conflict of interest; supporters see vertical integration of the future.

Skeptics and sector context

Helion is not the only fusion company drawing big checks. Commonwealth Fusion Systems, an MIT spinout pursuing the tokamak route, raised $863 million in 2025 from investors including Google and Nvidia. The flood of capital reflects genuine excitement — and, skeptics warn, a marquee valuation getting far ahead of an engineering bar no one has yet cleared. No company has produced commercial fusion electricity, and the gap between a $15.5 billion valuation and a working power plant remains vast.

What to watch

The milestones to track are concrete: progress on Orion’s construction, the looming 2028 deadline, and — above all — whether any of Helion’s offtake deals convert from contracts into actual electrons delivered to the grid. Fusion has never lacked for ambition or, lately, for money. What it has always lacked is a working commercial plant. Helion has bet $1.5 billion and its credibility that it can change that this decade.

Sources

1. TechCrunch — Helion raises $465M to build a power plant for Microsoft (June 4, 2026)
2. The Information — Fusion startup Helion nearly triples valuation to $15.5B (June 4, 2026)
3. GeekWire — Helion hits $15.5B valuation with $465M in new cash (June 2026)