SoftBank Group Corp.’s shares slid the most in nearly three months after the heads of Anthropic PBC and OpenAI called on developers to tap the brakes on artificial intelligence development for safety reasons.The warning heightened market jitters around the Japanese tech investor, which is taking on more debt to finance bets across the AI spectrum. SoftBank is one of OpenAI’s biggest backers, with its total investment in the ChatGPT maker slated to reach close to $65 billion by October.Shares of SoftBank fell more than 13 per cent Monday in Tokyo, their biggest intraday decline since late June. That’s as the company’s credit default swaps widened to the highest level since March 30, nearing three-year highs.Investors in both credit and equity markets are concerned about SoftBank founder Masayoshi Son’s unwavering faith in AI’s potential. He’s initiated a flurry of multibillion-dollar AI projects with uncertain timelines about payoff in revenue, dismissing talks about a possible bubble as “ignorant” and exposing his company to extreme volatility.That faith is being tested after Anthropic and OpenAI promised to rein in development of cutting-edge AI models following a series of disturbing security breaches. OpenAI co-founder Sam Altman also confirmed the startup will not list in 2026.SoftBank last week secured an $11.87 billion loan to bolster its investment in OpenAI, Bloomberg News reported. That’s on top of a ¥1 trillion ($6.5 billion) retail bond issue, a $10 billion loan linked to OpenAI shares and a potential bond sale of as much as $20 billion, as it finances deals such as the acquisitions of ABB Robotics and DigitalBridge. SoftBank’s also floated plans to build data centers around the world.The call to slow down frontier model development is exacerbating concerns around Son’s outsized bets to position himself at the center of AI growth. Shares of SoftBank are down around 30 per cent from a June peak, after Bloomberg News and other outlets reported OpenAI’s initial public offering could be delayed.They’ve also been hurt by concerns about heated competition and rising debt in the AI sector and a raft of hacks and other unsanctioned activity.“There’s worry that OpenAI’s value may not be as high as previously expected,” said Yugo Tsuboi, chief strategist at Daiwa Securities. “The market is on alert because we do not yet know how much the pace of AI development will slow down.”Doubts around AI’s investment prospects persist despite Anthropic chief Dario Amodei’s assurance that slowing the frontier development of AI capabilities won’t mean a slowdown in spending or growth. In the June quarter, SoftBank reported a profit, helped by big boosts from its stakes in Intel Corp. and TikTok developer ByteDance Ltd.What Bloomberg Intelligence SaysOpenAI’s delayed IPO, with CEO Sam Altman saying the company won’t go public this year, will defer SoftBank Group’s ability to monetize its 13 per cent stake and increase the risk of further capital commitments.Vision Fund 2 raised $10 billion through an OpenAI-linked margin loan, yet SoftBank had to provide a guarantee to secure the funds. SoftBank is probably funding a $26 billion bridge loan prepayment through an upsized two-year $12 billion loan, as reported by Bloomberg News, and margin loans, but might need more for a $10 billion OpenAI investment in October. -Sharon Chen, credit analystSoftBank also is accelerating repayment on some of its short-term loans. It said that it’s paying down the $25.9 billion balance on a $40 billion debt facility it obtained earlier this year to finance its investment in OpenAI by Tuesday, ahead of maturity in March next year.More stories like this are available on bloomberg.comPublished on September 14, 2026