Helion Energy, the Sam Altman-backed fusion startup, announced Thursday it has secured $465 million in a new Series G funding round, valuing the company at $15.5 billion. The round was led by Thrive Capital, with participation from new investors including Alta Park Capital, Anti Fund, BoxGroup, Lux Capital, and Peak XV Partners, as well as returning backers.
The fresh capital brings Helion's total funding to $1.5 billion, following a $425 million raise in January 2025. The company plans to deploy the funds toward completing Orion -- its first commercial fusion power plant -- which is being built to supply electricity directly to Microsoft's data centers as early as 2028.
A Different Kind of Fusion
Unlike most fusion research programs that rely on tokamak magnets (as in projects like ITER) or laser-based compression systems, Helion takes a distinct technical path. The company uses magnets to compress superheated plasma to fusion conditions, and plans to harvest electrical current directly from those same magnets as the plasma expands after fusion occurs. If this approach works at commercial scale, it could dramatically simplify the path from fusion reaction to usable electricity on the grid.
Helion has been running plasma experiments for several years and claims to have surpassed 100 million degrees Celsius -- the temperature threshold required for fusion conditions in its system. The company's seventh prototype, Polaris, is currently under development and is intended to demonstrate net electricity production before the Orion plant construction begins in earnest.
Why the Microsoft Deal Changes Everything
In 2021, Microsoft became one of the first major corporations to sign a power purchase agreement with a fusion energy company when it committed to buying electricity from Helion once its plant came online. With AI workloads consuming ever-larger shares of global power capacity, Microsoft has strong strategic incentives to support this timeline. Helion's fusion technology, if successful, would provide near-zero-carbon, baseload electricity well-suited to the continuous heavy demand of AI inference and training infrastructure.
Why It Matters
The race to power artificial intelligence is becoming one of the defining infrastructure challenges of this decade. Traditional renewable sources like wind and solar are intermittent, and nuclear fission plants take over a decade to permit and construct. Fusion, if it delivers on its technical promise, offers a path to abundant clean energy on a timeline that could intersect with AI's explosive power demand curve. Helion's $15.5 billion valuation and continued Microsoft backing signal that large institutional capital now treats fusion as a near-term commercial bet rather than a distant science project.
Whether Orion delivers grid electricity by 2028 or slips by a few years, the momentum behind fusion energy investment has never been stronger -- and enterprises planning their long-term compute infrastructure strategies should be paying close attention to how this race unfolds.