Helion Energy Inc., a pioneering fusion power startup, has raised $425 million in a Series F funding round, boosting its valuation to $5.245 billion. The round saw participation from Lightspeed Venture Partners, SoftBank Vision Fund 2, an unnamed university endowment, and existing investors, including Sam Altman, who previously invested $375 million in the company.

Unlike traditional nuclear fission, which splits heavy atoms to release energy, fusion merges light atoms to form heavier ones, potentially generating far more power. However, commercializing fusion has remained elusive due to the immense heat and pressure required to overcome atomic repulsion. Helion, based in Everett, Washington, is tackling this challenge with its magneto-inertial fusion technology, which it believes can unlock practical fusion energy.

Helion’s fusion reactor is a tube-shaped device lined with magnets. At each end, it stores plasma fuel made from deuterium and helium-3. The fusion process unfolds in multiple stages: first, magnets mix the plasma, then accelerate it toward the tube’s center at a staggering speed of 1 million miles per hour. Upon collision, another set of magnets compresses the fuel, heating it to over 100 million degrees Celsius—triggering fusion. The resulting expansion of the fuel alters the surrounding magnetic field, generating electricity. The process repeats in rapid pulses multiple times per minute.

In 2021, Helion achieved a significant breakthrough with its Trenta prototype, which became the first privately developed reactor to reach the crucial 100-million-degree threshold for commercial fusion. The company has since developed Polaris, a more advanced prototype expected to demonstrate electricity generation from fusion for the first time.

CEO David Kirtley emphasized Helion’s role in shaping the future of energy, stating, “We are on the brink of delivering a transformative energy solution that can meet the world’s increasing electricity demands while preserving U.S. energy leadership.”

The newly secured funding will enable Helion to enhance its manufacturing capabilities, particularly by producing capacitors—key energy storage components—in-house, rather than relying on external suppliers. This move is expected to accelerate reactor production significantly.

In addition, the capital will support the development of a 50-megawatt fusion power plant commissioned by Microsoft in 2023, slated to come online by 2028. Helion has also signed an agreement to build a 500-megawatt plant for Nucor Corp., a leading steel manufacturer that participated in the funding round.

With its cutting-edge technology, strategic partnerships, and strong financial backing, Helion is positioning itself as a leader in the race to bring commercial fusion energy to the world.