MIT spinout Commonwealth Fusion Systems (CFS) has raised more than $1 billion, Axios Pro reports.
The investment in the company, which hopes to build functioning 400MW fusion reactors in less than a decade, was led by an unnamed hyperscale developer.
While it is not known which company led the round, both Microsoft and Google have previously invested in the business. Microsoft is also CFS' cloud provider.
Late last year, CFS said that it planned to build 'ARC,' a grid-scale fusion power plant in Chesterfield County, Virginia, for the early 2030s. It hopes to have a smaller test system, 'SPARC,' by 2027.
In March, the company said that it had successfully installed the cryostat base, essentially the foundation of what will form the tokamak reactor.
Currently, no company or state has managed to build a fusion reactor that has achieved net power, although Lawrence Livermore researchers have achieved net energy gains in a fusion ignition breakthrough.
With timelines unknown, and vast capital investments required, fusion investments remain a challenge. This month, the UK's First Light Fusion saw its value slashed by 60 percent as it abandoned plans for a prototype power plant due to funding challenges.
The CEO of Canada's General Fusion similarly said that he was forced to lay off workers as investments dried up, with about a quarter of staff thought to have been let go.
"Today’s funding landscape is more challenging than ever as investors and governments navigate a rapidly shifting and uncertain political and market climate," CEO Greg Twinney said.
"Keeping a fusion company funded in today’s world requires more than just meaningful capital. It takes ambition, steadfast patience, a bold national vision aligned with the opportunity, and constant refreshing of the investor base as timelines stretch beyond typical fund horizons."
Some companies have managed to raise funds despite the broader challenges. Alongside CFS' raise, Realta Fusion this month raised $36 million in a round led by Future Ventures to start building its own Anvil prototype.
