In January 2025, Helion Energy closed a $425 million funding round. Less than six months later, the Everett, Washington startup has returned to investors for more — this time securing $465 million in a Series G round led by Thrive Capital, pushing its valuation to $15.5 billion and its total capital raised to $1.5 billion.

The urgency is not hard to explain: Helion is in a race against its own promise. Under the terms of a landmark agreement with Microsoft, the company has committed to delivering fusion-generated electricity to the grid as early as 2028 — a deadline that would have seemed fantastical to most physicists just a decade ago. What makes Helion unusual is not only the timeline but the underlying engineering philosophy. Most fusion companies — whether they use powerful magnets or high-energy lasers to trigger reactions — plan to extract electricity through steam turbines, converting intense heat into mechanical motion and then into current.

Helion rejects that approach entirely. Its reactor compresses deuterium and helium-3 fuel using magnets, and when the resulting fusion plasma expands, it pushes back against those magnetic fields. That force is harvested directly as an inductive electrical current — a principle not unlike the regenerative braking system in an electric vehicle, where motors run in reverse to recover energy.