TOKYO, Sept. 23 -- Masayoshi Son's current bet is being framed as far larger and more concentrated than his earlier Vision Fund investments, whose exposure to companies such as WeWork and Uber contributed to losses exceeding $70 billion.

After years of rebuilding, Son is now pursuing a strategy that makes those earlier wagers appear comparatively cautious. The line captures both the scale of his renewed ambition and the risk of staking so much on a single idea.

SoftBank Group launched a record bond offering on Monday, seeking $10 billion in dollar-denominated notes and €1 billion in euro-denominated securities to fund the third and final tranche of its $30 billion follow-on investment in OpenAI. The deal, structured across five tr...