Helion Energy on Tuesday said that it added $35 million to a funding round initially announced in June. The Everett, Wash.-based fusion company originally shared news of a $465 million Series G round.
“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 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. It has raised more than $1.5 billion to date.
Last week Helion celebrated the opening of its first office in downtown Seattle as its headcount tops 800 employees.
The company is racing to hit an ambitious timeline, having signed a deal with Microsoft three years ago to supply energy to a Central Washington data center by 2028. The company broke ground on the 50-megawatt plant, dubbed Orion, in July 2025.
But Helion’s timing for hitting that energy target remains uncertain. When it announced the agreement with Microsoft, the company stated that 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 recently reported that full capacity might not be hit until 2030, according to a Helion executive. The news site also cited two scientific publications by plasma physicists questioning the company’s ability to produce a sufficient amount of energy from its fusion devices to power the grid, though Helion has responded to concerns raised by both on its FAQ site.
That said, Helion is hustling to resolve technical challenges. GeekWire in May reported on Tiny Merge, a small-scale testbed device the company is building at its R&D facility to answer questions its larger, more expensive prototypes haven’t — questions that need answers before final power plant designs are locked in.
Kirtley, however, remains bullish on the company’s trajectory and the vote of support 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.”
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