Helion's Series G Grows to $500M as Microsoft Deadline Looms

Helion Energy has added $35 million to its Series G round, lifting the total to $500 million and pushing the fusion startup's overall fundraising past $1.5 billion. The Everett, Washington-based company announced the top-up on Tuesday, three months after initially disclosing a $465 million round in June.

"After initially closing the round earlier this summer, we are excited to bring on several new investors and to have a round that includes crossover, pension, and sovereign wealth investors," said David Kirtley, Helion's co-founder and CEO, in a post on LinkedIn. Kirtley said the investment now totals $500 million.

The June round valued Helion at $15.5 billion, according to GeekWire's earlier reporting. The company aims to be the first in the world to commercialize fusion, replicating the reactions that power the sun and stars to produce nearly limitless clean energy.

Can Helion meet its Microsoft deadline?

The funding arrives as pressure mounts on the startup's most consequential commitment. Three years ago, Helion signed a deal with Microsoft to supply energy to a Central Washington data center by 2028. The company broke ground on the 50-megawatt plant, dubbed Orion, in Malaga, Washington, in July 2025.

The clock is a concern. When Helion announced the Microsoft agreement, it said Orion was "expected to be online by 2028 and will target power generation of 50 MW or greater after a 1-year ramp up period."

Axios reported on September 8 that full capacity might not arrive until 2030, according to a Helion executive. The outlet also cited two scientific publications by plasma physicists questioning whether Helion's fusion devices can produce enough energy to power the grid. Helion has responded to both sets of concerns on its FAQ site.

What is Helion doing to close the technical gap?

The company is hustling to resolve open questions before final power plant designs are locked in. GeekWire reported in May on Tiny Merge, a small-scale testbed device Helion is building at its R&D facility to answer questions its larger, more expensive prototypes have not.

The company is also scaling its organization. Last week Helion opened its first office in downtown Seattle as its headcount tops 800 employees.

Kirtley remains bullish on the company's trajectory and the vote of confidence from investors.

"Technical milestones remain the most important to me and the company," he said, "but this new funding demonstrates the growing demand for, and confidence in, fusion energy and Helion's ability to deliver fusion energy to the grid."

The fresh capital buys Helion runway for its bet that it can solve the physics, hit the 2028 deadline, or at least land close to it — with Microsoft's data center waiting on the other end.