In his newly built palace near Tokyo, lined by stone statues of Roman emperors and surrounded by an 18-hole golf course, Masayoshi Son was stewing. After declaring for years the imminent arrival of the artificial-intelligence revolution,

Seattle-area company Helion Energy gets $425 million from investors including Sam Altman and Softbank to pursue clean energy's "Holy Grail."

A US start-up whose backers include tech billionaires Sam Altman and Peter Thiel has raised $425mn to keep it on track to achieve its target of producing electricity from nuclear fusion in 2028. Helion has the most ambitious timeline among start-ups racing to develop nuclear fusion,