AI Debt Boom Rattles Markets as Returns Stay Unproven

CoreWeave, an AI cloud company carrying about $50 billion in debt, saw its shares tumble this week as investors asked a blunt question: Who will pay for the artificial-intelligence build-out, and what will they get back? The selloff has clipped a bull market that just marked its fourth anniversary. It also exposes how much of the AI boom now rests on borrowed money.

The jitters spread fast. Semiconductor firms and technology hardware companies, including Dell Technologies, posted sharp declines. Strategists at Deutsche Bank and RBC Capital Markets each cut their recommendations on the technology sector. On October 9, Deutsche Bank strategists said the rotation into technology had "run far and the risk-reward no longer looks favorable in the near term."

The Debt Behind the Boom

The worry isn't abstract. The Financial Times reported that investors are uneasy about technology companies borrowing heavily to build data centers without a clear understanding of how they'll make money from them. Goldman Sachs estimates that Meta and four other AI hyperscalers will together lift capital spending to about $1.2 trillion next year.

That's a staggering sum. And borrowing is getting pricier. "With the cost of capital going up, this capex blowout is going to become more expensive, which raises the bar for returns," said Chuck Carlson, chief executive officer at Horizon Investment Services. Kevin Shea, senior equity analyst at BNY Wealth, put the test plainly: whether hyperscaler profitability "can grow faster than the pace of their capex."

Katie Martin, the FT's markets columnist, said South Korea's semiconductor-heavy stock market fell 8% in a single session, with selling carrying into Europe and, to some extent, the United States. She described the AI trade over the previous 12 to 18 months as driven in large part by "hype and vibes." She said it's unclear whether this is a short-term wobble or the start of something more serious.

Credit Ratings and Opaque Finances

The FT also reported that Anthropic received a double-B grade from Kroll Bond Rating Agency in June, based on documents its reporters saw. The rating hadn't been publicly reported before. It put the AI lab close to investment grade, though KBRA didn't have full access to Anthropic's financial information. KBRA and Anthropic declined to comment.

The details deserve scrutiny. KBRA used an in-house credit risk score, described as rare for a credit rating, and received only a limited set of financials. Bankers acting for Anthropic had lobbied for an investment-grade rating after the company goes public. Michelle Chan, the FT's US credit correspondent, said such a rating could lower borrowing costs and widen access to capital after an IPO. She also noted that KBRA isn't one of the three major credit rating agencies, and the others might not give Anthropic as much leeway. CoreWeave, for its part, wanted an investment-grade rating on its bonds, which a senior executive said could help it tap insurance-company capital.

Earnings Season Becomes a Test

Wall Street now turns to results from Meta Platforms, Lam Research and Texas Instruments, along with Tesla, Netflix, Procter & Gamble and GE Aerospace. LSEG IBES forecasts S&P 500 companies will grow third-quarter earnings by more than 30%. Meta, with a market capitalization of about $1.9 trillion, has seen its shares rise in recent weeks after launching its Muse AI assistant.

The broader market has held up. The S&P 500 sits about 1% below its record high set this month, and sectors that lagged during the tech climb have begun picking up the slack. But Garrett Melson, portfolio strategist with Natixis Investment Managers Solutions, described a lopsided market. "This is very much an on-off switch type of market," he said. "When AI is working, it sucks all the oxygen out of the room for the rest of the sectors."

The Philadelphia SE Semiconductor index has fallen 8% this month but remains up more than 60% for the year, against a 13% year-to-date gain for the S&P 500. Lam Research and Texas Instruments, due to report Wednesday, have each risen about 60% in 2026. Rising Treasury yields and the possibility of further Federal Reserve rate increases still weigh on investors. Hot inflation data this week increased bets on another increase at the Fed's end-of-October meeting, though futures pricing shows most investors expect the central bank to wait until December to raise rates for a second time this year. UBS Global Wealth Management analysts said in a Thursday note that "another strong earnings season should help equities withstand moderately higher rates."

Why This Matters:

The AI build-out increasingly relies on debt, and those exposed to it extend well beyond Silicon Valley. CoreWeave's interest in tapping insurance-company capital shows how risk can reach institutions that hold retirement savings and policy reserves. When agencies issue ratings based on limited financials and bankers lobby for better grades, basic questions arise about transparency and who's checking the math. Meanwhile, Melson's "on-off switch" warning points to a market where gains are concentrated in a handful of giants, leaving other sectors starved for attention and investment. Hot inflation and talk of more rate increases mean ordinary borrowers feel the squeeze too. If returns on $1.2 trillion in spending don't materialize, the fallout won't stay on trading floors. It's a reminder that markets this large and this leveraged need clear disclosure and credible oversight, because the costs of a bad bet rarely land only on those who made it.