Masayoshi Son Is Going Big on OpenAI. Time to Worry.

When Masayoshi Son bets big, it either marks the dawn of an era, or the dusk of a tech cycle.

The chairman of SoftBank Group Corp. has enjoyed some spectacular wins. Spotting Alibaba Group Holding Ltd. early handed SoftBank $58 billion when the Chinese e-commerce firm went public a decade ago. A $32 billion take-private deal of ARM Holdings Plc in 2016, followed by a timely listing of the chip designer in 2023 when the AI theme took off, gave Son another windfall. ARM now accounts for roughly half of SoftBank’s portfolio value.