Fusion startup Helion has raised $425 million in a Series F round.
The round saw Lightspeed and SoftBank Vision Fund 2 invest in the company, alongside participation from existing investors, including Sam Altman, Mithril Capital, Capricorn Investment Group, Dustin Moskovitz through Good Ventures Foundation, and Nucor.
The raise values the business at $5.245 billion.
"I am very excited for what this funding will enable for us," CEO David Kirtley said.
"We will be radically scaling up our manufacturing in the US – enabling us to build capacitors, magnets, and semiconductors much faster than we have been able to before. This accelerates the construction of the world’s first fusion power plant and then all our plants to come."
Last month, Helion deployed its latest prototype, Polaris, after three years of development.
Nuclear fusion, the same process that powers the sun, could theoretically provide abundant zero-emissions electricity without the risk of nuclear accidents as present in nuclear fission. So far, however, company and state-backed approaches have struggled to generate more energy than they consume.
Back in 2023, Microsoft signed a 50MW power purchase agreement (PPA) with Helion for 2028 - a short time in fusion development timescales. OpenAI, led by Helion investor Sam Altman, is also thought to be looking to buy "vast quantities" of fusion power.
Rival Commonwealth Fusion Systems last month said that it hoped to build a 400MW 'ARC' power plant in Virginia in the early 2030s.
