SoftBank wires the final $10B to OpenAI: Son's cumulative bet hits $64.6B for a 13% stake

The single biggest corporate bet on frontier AI just made its final payment. SoftBank Group announced on October 1 that it has wired the third and final $10 billion tranche of its follow-on investment in OpenAI, completing the $30 billion commitment the Japanese conglomerate unveiled in February. In a year of splashy AI fundraising headlines, this is the mirror image: the investor finishing what it promised, right on the timetable it set seven months ago.

The numbers are the story. With this payment, SoftBank's cumulative investment in OpenAI totals $64.6 billion, buying it an ownership interest of roughly 13% — the largest known single stake in any frontier AI lab.

The deal, in numbers#

The tranche was executed through SoftBank Vision Fund 2 on October 1 (Japan time), according to SoftBank's own announcement. It closes out the “follow-on investments in OpenAI” package disclosed on February 27, 2026: $30 billion in three installments, now fully paid. The aggregate $64.6 billion figure counts everything SoftBank has put into the ChatGPT maker to date, and the company says it now holds approximately 13% of OpenAI Group PBC.

That is a staggering ownership share for a company that, unlike its peers, is still controlled by a nonprofit board — and it makes Masayoshi Son's conglomerate the closest thing frontier AI has to an anchor shareholder.

Paid for with the biggest junk-bond sale on record#

SoftBank did not pay from cash. The $10 billion tranche was funded with the proceeds of the foreign-currency senior notes the company priced on September 24: $10 billion in dollar-denominated notes split across three maturities — $1 billion due in 2030 at 8.625%, $4.5 billion due in 2032 at 9.25%, and $4.5 billion due in 2034 at 9.75% — plus €1 billion in euro-denominated notes due in 2030 and 2032 at 7.125% and 8%.

The dollar tranches alone will cost roughly $941 million a year in interest — real money, and the coupon rates tell their own story. This is speculative-grade debt: the notes carry BB+ ratings from S&P and Fitch's Japanese arms, and Reuters described the $11.1 billion offering as the largest high-yield corporate bond sale on record globally. Son is, in effect, buying equity in the AI future on margin, at junk-bond prices, and the meter is running.

The $40 billion bridge is closed#

Equally telling is what SoftBank unwound. The March 2026 bridge facility — $40 billion of short-term credit that financed the earlier tranches — is now fully repaid. SoftBank had already made an early repayment on September 9; on September 30 it canceled the remaining $10 billion of undrawn capacity. As the company put it: all borrowings repaid, no undrawn commitments remain.

The financing structure has quietly shifted from temporary bridge credit to permanent, long-dated bonds. Whatever happens next in AI, SoftBank's OpenAI exposure is now locked in for the better part of a decade.

Why Son is all in#

This is not a portfolio bet — it is the bet. OpenAI is far and away the largest position in SoftBank's orbit, and the capital underwrites the single most expensive constraint in AI: compute. The payment lands the same week OpenAI is reportedly closing a separate $30 billion funding round at a $1.4 trillion valuation, which means SoftBank's ~13% stake was acquired at an average entry well below the latest mark — assuming that valuation holds.

But the entry price is not the whole story. At roughly a billion dollars a year in interest on the new notes, SoftBank's position has to appreciate just to stand still. Son is paying junk-bond yields for equity exposure, which is another way of saying he believes the upside in frontier AI dwarfs the carrying cost. It is the defining wager of the AI era, financed like a leveraged buyout.

What to watch#

Governance, not just economics. What does 13% actually buy in a company still ultimately controlled by a nonprofit? OpenAI's unusual structure has already survived one boardroom meltdown; whether the largest shareholder carries conventional rights or something weaker is the question every future investor in the capital structure will ask.

The refinancing risk. The notes are long-dated, but they are not cheap, and SoftBank's balance sheet now carries the weight of the position. If AI valuations stumble, the interest bill does not care.

What the money builds. The capital thesis is compute — and the race is physical now: data centers, chips, energy. Whether $64.6 billion of Son's conviction translates into the infrastructure OpenAI needs to defend a $1.4 trillion valuation is the test that will take years to grade.