The bill for SoftBank’s wager on OpenAI has come due, and the Japanese group has turned to the junk-bond market to pay it.
SoftBank confirmed in a filing on Sept. 24 that it had raised $11.1 billion across dollar- and euro-denominated notes. The proceeds, the company said, will cover the final $10 billion of the $30 billion it committed to invest in OpenAI, taking its total investment in the artificial-intelligence company to $64.6 billion once complete.
The dollar portion came in three senior tranches: $1 billion of 3.5-year notes at 8.625 percent, $4.5 billion of 5.5-year notes at 9.25 percent, and $4.5 billion of 7.5-year notes at 9.75 percent. Two euro tranches of 500 million euros each, with four- and six-year maturities, priced at yields of 7.125 percent and 8 percent.
Those coupons are high, even for a company that has long relied on high-yield borrowing. According to LSEG data, the sale is the largest high-yield corporate bond issuance on record globally, surpassing the $10.9 billion that French telecom operator Numericable raised in 2014. SoftBank shares rose more than 7 percent on the day.
The financing is the latest sign of how the AI boom is reshaping corporate borrowing. SoftBank has already issued $14.6 billion in high-yield bonds so far in 2026, accounting for 63.4 percent of the Asia-Pacific and Japan high-yield market, according to LSEG data cited by Reuters. It has also sold assets and taken out loans backed by its stakes in chip designer Arm and in OpenAI itself.
The coupons also reflect a market that is asking more of risky borrowers. Yields on new high-yield issues were hovering around their highest levels in at least a year in the days before SoftBank printed, according to Barron’s, and SoftBank’s spreads carry a premium for the size of the ask. Investors took the deal anyway, a sign that appetite for AI-linked debt has not yet cracked.
The urgency has a specific cause. SoftBank had hoped to fund part of its commitments through public listings of OpenAI and of its data-centre subsidiary SB Energy. Both delayed IPO plans that had been expected as early as this month, leaving the bond market to fill the gap.
The relationship behind the borrowing is one of the defining bets of the AI era. SoftBank led OpenAI’s $40 billion funding round in 2025, which valued the company at $300 billion, and completed the final $22.5 billion tranche in December that year. A later secondary sale implied a valuation closer to $500 billion, according to data providers tracking private markets. SoftBank now holds a stake of roughly 11 percent, making it one of OpenAI’s largest shareholders.
Masayoshi Son, SoftBank’s founder, has staked much of his firm’s reputation on the bet. He framed the OpenAI investment as the centre of SoftBank’s future and has poured capital into the surrounding infrastructure, including Stargate, the data-centre venture SoftBank and OpenAI are building with Oracle and others and which was announced in January 2025 at a projected $500 billion.
SoftBank is not alone in borrowing for AI. Hyperscalers including Amazon and Alphabet have also expanded their debt sales this year, increasingly tapping euro and other currencies alongside dollars to spread their financing across markets. The sums involved have turned AI into one of the biggest single drivers of corporate bond supply.
The question hanging over the sale is how far SoftBank can stretch its balance sheet. Its commitments now run well beyond the OpenAI stake, into data centres and the infrastructure that surrounds the models themselves. Each dollar raised through debt adds to a repayment schedule that assumes the AI boom keeps paying off.
The bet also carries echoes of Son’s earlier swings, when SoftBank borrowed heavily to back startups through its Vision Fund and suffered painful writedowns when markets turned. Analysts said the OpenAI stake now plays a similar role on the group’s balance sheet: a large, concentrated position financed in part by debt, whose value swings with sentiment toward AI.
The record issue also marks a change in how the sector funds itself. AI companies and their backers once leaned on equity rounds and venture money; now the public debt markets are absorbing an increasing share of the cost, from SoftBank’s junk notes to investment-grade sales from the hyperscalers. The yield SoftBank paid is the clearest sign that lenders want to be compensated for how much is being asked.
For now, investors are betting it will. The bond that closed this week is a measure of how much the market is willing to lend against that assumption, and of how central one company’s OpenAI stake has become to the whole sector’s financing. The group has used the high-yield market for years to fund acquisitions and buybacks, and lenders have rarely balked; the size of this ask simply pushed the deal into record territory.
