Helion , the fusion startup backed by Sam Altman, announced on Thursday that it had raised $465 million in a new funding round that values the company at $15.5 billion. The cash infusion lands as Helion is racing to complete Orion, its first power plant. The startup has set an aggressive timeline to deploy fusion power to the grid, as early as 2028 if it can deliver on the terms of its deal with Microsoft .  The startup last raised $425 million in January 2025 . Altogether, Helion said it has