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."

With the latest round of funding, Helion has raised over $1 billion in capital since it was founded in 2013. The company claims that it will build the world's first nuclear fusion power plant by 2028 and has already secured a purchase agreement from Microsoft which is a major investor in Mr Altman's OpenAI.