SoftBank’s $64bn OpenAI bet turns the Japanese giant into a tech roulette

How Masayoshi Son’s SoftBank conquered Japan’s market cap crown

In June 2026, SoftBank did something that once seemed improbable: it dethroned Toyota to become the largest company by market capitalisation in Japan. The ascent was fuelled not by a breakthrough in semiconductors or robotics—SoftBank’s best-known holdings include chip designer Arm—but by the market’s faith in founder Masayoshi Son’s newest, and easily his most concentrated, gamble. Son has committed $64 billion to OpenAI in return for a 13% stake, a deal that makes his group the AI start-up’s most important backer.

For anyone who has watched SoftBank since its birth as a software distributor in 1981, the move is both classic Son and extraordinarily risky. He has spent three decades hunting the next technological wave, from the PC era to the internet and mobile, and he has found some genuine gems. SoftBank was the early investor that helped launch Alibaba into the stratosphere, it brought the iPhone to Japan, and it owns Arm, whose designs power nearly every smartphone on the planet.

Yet the same instinct has produced colossal failures. The most notorious is WeWork, the co-working start-up that Son poured billions into and that spectacularly imploded in 2019. Even so, Son describes brushes with annihilation—the dot-com crash that almost wiped him out, the 2008 crisis, the pandemic—as mere potholes. “We almost went bankrupt, and surprisingly, I survived,” he once said. At 69, with no clear successor despite a life plan that promised one by his sixties, he continues to steer SoftBank with a tight grip and, reportedly, an email address that leaves no doubt who is in charge.

The OpenAI bet now dwarfs everything that came before. SoftBank’s fortune has become inextricably tied to whether OpenAI can deliver on the promise of artificial general intelligence—and whether public markets will eventually assign it the valuation Son clearly believes it deserves. Until then, the world’s biggest tech investor is effectively riding on a single name.

A singular bet on a single company—what history and personality tell us

The investment logic—and the concentration nightmare

SoftBank’s $64 billion injection gives it a minority stake that is still large enough to make OpenAI its dominant driver of future returns. The structure is reminiscent of the Alibaba investment: a massive early bet on a category-defining asset. Alibaba turned a $20 million stake into tens of billions and cemented Son’s reputation as a visionary. But the difference today is scale and timing. SoftBank is writing a cheque more than 3,000 times larger for a company that, by its own admission, has pushed back an IPO because markets seemed unwilling to match its private valuation. That leaves SoftBank holding an illiquid position whose paper value can swing violently with investor sentiment around AI.

What the delayed IPO really signals

OpenAI’s decision to postpone a listing is the detail that should worry SoftBank watchers most. A company that struggles to convince public-market investors of its worth forces its main backer to absorb all valuation uncertainty. For SoftBank, that means a large part of its own market cap—which has already leaped past Toyota’s—is predicated on a price that public investors have effectively refused to validate. If the AI narrative cools or a rival leapfrogs OpenAI, SoftBank’s concentrated bet could trigger a drawdown as brutal as the WeWork collapse, but on a far larger nominal scale.

Son’s leadership and the missing succession plan

Masayoshi Son is SoftBank’s greatest asset and its biggest governance risk. The story of his childhood encounters with racism, which reportedly fuel a desire to overturn the Japanese establishment, also explains a leadership style that tolerates no heir. Potential successors such as former Google executive Nikesh Arora were sidelined. At 69, Son still holds every lever, a reality that makes SoftBank’s long-term direction inseparable from one man’s judgement. A biographer has called him one of the most secretive business figures he has ever met. For a group betting the house on a single asset, that opacity compounds the risk.

Lessons from history: boom, bust, and the survivor

SoftBank has repeatedly ridden valuations to dizzying heights only to see them collapse. Son was briefly the world’s richest person in early 2000 before the dot-com crash erased 99% of his paper wealth. The financial crisis and the WeWork debacle inflicted further deep wounds. Each time, Son rebounded because the group’s underlying telecom operations generated steady cash and because a few outsized winners—Alibaba, Arm—more than compensated for the losers. The OpenAI bet tests whether that model can work when the entire edifice rests on one name, not a portfolio.

What SoftBank’s OpenAI wager means for investors and the group itself

• For investors holding SoftBank shares: the group’s valuation now moves in lockstep with sentiment around OpenAI. Watch for any sign of further IPO delays or secondary market transactions that imply a lower private valuation—they will feed directly into SoftBank’s market cap, as seen after the WeWork write-downs.
• For creditors and bondholders: SoftBank’s debt profile has been a persistent concern. A $64 billion concentrated equity bet raises questions about liquidity and collateral, especially if a downturn in AI stocks reduces the value of the group’s holdings. The company’s next borrowing costs and covenant disclosures deserve close scrutiny.
• For SoftBank’s board and leadership: the OpenAl commitment makes an orderly succession plan more urgent than ever. The group’s historical pattern of boom-bust cycles and Son’s unwillingness to designate a number two increase the probability that a crisis would arrive with no clear decision-maker other than the founder.