Tech Billionaires Bet on Fusion as Holy Grail for Business

Sam Altman became a tech sensation this year as the CEO of OpenAI, the artificial-intelligence startup that seems pulled from science fiction. But Mr. Altman, who has been among Silicon Valley's most prominent investors for more than a decade, has placed one of the biggest bets of his career on a company that might be even more futuristic: a nuclear-fusion startup called Helion Energy Inc.