US Market Breakdown: AI Debt Fears Rout the Chips, Week of 12 October 2026

The AI trade cracked last week, and it cracked over money rather than technology. A hotter-than-expected pair of US inflation reports pushed the cost of capital higher just as investors started asking how the companies building AI data centres intend to pay for them. The Nasdaq Composite fell 4.48% over the week to 26,140.03, its worst week since June, while the S&P 500 lost 1.95% to close at 7,659.44. Chip stocks were the epicentre: the sector shed 11.41% across the five sessions.

The Dow Jones Industrial Average went the other way, adding about 0.7% to 52,002.41 for a second consecutive weekly gain, because the money leaving semiconductors went into consumer staples, energy and healthcare rather than out of the market altogether.

Monday's session, the most recent to close, took some of it back. The Nasdaq rose 1.11% to 26,430.89 and the S&P 500 gained 0.41% to 7,690.73, while the Dow slipped 0.07% to 51,966.03 — a rebound concentrated almost entirely in the names that had just been sold hardest.

Wall Street

The week began badly for memory makers and got worse from there. On Monday 12 October, memory and storage shares fell after China's CXMT said it had progressed a denser DRAM design and intended to build server memory on it by the end of 2026 — server memory being the most profitable corner of that market. Micron closed at $989.04, down 3.9%.

Tuesday brought the start of third-quarter earnings season proper, with the big banks reporting, and the index held together. Wednesday was the turn. September CPI landed hotter than forecast, the Nasdaq fell 1.9%, and CoreWeave — the AI "neocloud" that rents out computing power — dropped 15.46% to $65.78 as its bonds sold off.

Thursday looked like a reprieve and was really a rotation: the Dow rose more than 500 points while the AI complex kept bleeding, the VanEck Semiconductor ETF falling 2% for an eighth consecutive losing session. By Friday the rotation had become a rout. The Nasdaq slid about 2%, the Philadelphia semiconductor index fell 3.8% for its own eighth straight decline, and the Russell 2000 ended the week down roughly 3% at 2,721.37. The VIX closed at 19.99, its highest since 29 July.

Monday 19 October reversed the direction without reversing the breadth problem. The Philadelphia semiconductor index rose more than 2.7%, snapping an eight-session run that had cost it about 15.7%, and the VanEck Semiconductor ETF added nearly 3%. Yet decliners outnumbered advancers on the New York Stock Exchange and most S&P 500 constituents fell. The 10-year Treasury yield barely moved, at about 5.08%.

The week's biggest movers

CoreWeave was the week's defining story, down roughly 25% across the five sessions. The trigger was its debt rather than its business: the yield to maturity on its 9.625% notes due 2032 climbed to 14.8% and then 15.77%, and five-year credit default swap spreads widened to 1,140 basis points. A Gartner forecast that cost pressure and thin differentiation would force more than 80% of neocloud providers to cease independent operations by 2030 arrived in the middle of it. Chief executive Mike Intrator pushed back, saying the company was "confident in our backlog which more than supports all of our debt obligations". Shares fell 10% on Friday alone, then edged up more than 1% on Monday after Goldman Sachs upgraded the stock to buy.

Micron lost around 11% over the week on the CXMT news and broader worries about memory oversupply later this decade, including a 5.6% fall on Friday. Rosenblatt's Kevin Cassidy argued the Chinese developments would not "swing the supply-demand equation at all" — a view the tape ignored until Monday, when Micron rose almost 4%.

Bank of America fell 7% on Wednesday after third-quarter profit dropped sharply, weighed down by a $1.2bn penalty from the US Treasury Department over money-laundering violations.

FMC, the agricultural chemicals group, was the week's worst single blow-up, collapsing 32% on Thursday after third-quarter revenue guidance came in sharply below the FactSet consensus.

Bumble jumped 56% on Tuesday after agreeing to be taken private by Ithaca Holdings in an all-cash deal valuing the dating app at $1.3bn.

Amazon had its best day in three months on Monday, gaining about 5% after Morgan Stanley named it a top pick and lifted its AWS growth forecasts. Palantir added about 4.4% the same day, and Cleveland-Cliffs rose 16% on third-quarter adjusted earnings of 28 cents a share against a FactSet estimate of 21 cents.

Company news in focus

Beyond the price action, the week was unusually busy for corporate news. IonQ fell 8% on Wednesday after announcing a $2bn equity offering — a reminder that the capital-raising question is not confined to AI cloud providers. Kimberly-Clark had a better week on two fronts: it rose about 4% on Thursday after preliminary third-quarter results beat estimates, and the European Commission cleared its $40bn acquisition of Kenvue after the company offered concessions to address antitrust concerns.

Meta gained more than 3% on Monday 12 October after unveiling a new AI model it calls Muse Wonder, and added again the following session. Oracle stayed in the frame for less comfortable reasons: a New York Times survey of the AI build-out's bottlenecks, summarised on 19 October, used its New Mexico campus as the example, noting that after local opposition blocked a power-supply permit Oracle told its landlord Blue Owl Capital it could not pay rent. Oracle had sent a force majeure notice to Blue Owl's development unit in late September.

Analyst moves did real work in a jumpy market. Datadog rose about 6% on Monday after Bernstein upgraded it to outperform, with analyst Peter Weed citing AI tailwinds. Western Digital climbed around 6% the same day on the storage rebound and a ratings upgrade, after a bruising run driven by CXMT and concerns over Toshiba expanding hard-disk output. Nvidia held up better than its peers on Friday, rising slightly in pre-market trade while AMD and others slipped, with chief executive Jensen Huang saying customers were placing AI chip orders almost daily.

Earnings in focus

The banks set the tone on Tuesday and Wednesday, and they did not set it uniformly. Goldman Sachs reported third-quarter earnings of $17.01 a share against an LSEG consensus of $13.02, on net revenue of $18.68bn — its second-best quarter on record. Equities revenue surged 72% to $6.44bn on financing and derivatives, while fixed income slipped 1% to $3.47bn and advisory fees hit a record $1.65bn, up 18% year on year.

JPMorgan delivered a rare miss, with earnings of $5.57 a share on revenue of $50.2bn against expectations in the $5.82–$5.91 range; the shares finished roughly flat. Morgan Stanley beat, reporting $3.03 a diluted share against $2.80 a year earlier with equities trading revenue up 41% to $5.8bn, and the stock still fell about 3% on Wednesday. BlackRock rose 3% in pre-market trade on an earnings and revenue beat.

TSMC produced the quarter of the week on Thursday, posting a record net profit for a sixth straight quarter at NT$763.06bn, up 68.7% year on year and ahead of the NT$746.3bn analysts expected, on revenue of NT$1,494.24bn (about $46.7bn). High-performance computing, which covers AI accelerators and data-centre processors, made up 68% of revenue, and the company raised its full-year 2026 revenue growth guidance to about 44%. Gross margin of 66.4% was ahead of guidance but down from 67.7% as the 2-nanometre ramp diluted returns, and the US-listed shares eased.

Johnson & Johnson beat on Tuesday with adjusted earnings of $2.59 a share against $2.53 expected and revenue of $25.4bn, up 5.9%, and raised full-year adjusted earnings guidance to $11.05–$11.15 a share on revenue of $101bn–$101.4bn. Reported earnings were just $0.09 a share after a one-time charge for the proposed talc litigation resolution.

Sectors in focus

The headline index fall disguised how narrow the damage was. Only four of the eleven S&P 500 sectors fell on the week. Consumer staples led with a 5.02% gain, energy added 4.86%, healthcare 3.45%, materials 3.01%, utilities 1.93% and financials 1.44%. Within staples, Coca-Cola rose 6.64%, Walmart 6.70% and Procter & Gamble 5.37%, a straightforward consequence of money leaving growth. On Friday alone, communication services fell 2.7% and information technology 2.4%.

That the S&P 500 could lose only 1.95% while its largest sector dropped 7.70% is the clearest available measure of how top-heavy the index has become — and FactSet's 16 October earnings update put a sharper number on it. With 9% of the index reported, blended third-quarter earnings growth stood at 29.0%, down from 29.4% a week earlier, with 84% of reporters beating on earnings per share. Strip out just two companies, Micron and Nvidia, and that 29.0% falls to 20.0%. Nvidia alone shed roughly $365bn of market value over the week, about £274bn at the week's exchange rate of around $1.33 to the pound, and CNBC reported that the 20 most valuable global AI and semiconductor stocks lost more than $1tn between them.

Macro and the Fed

Two inflation prints did the damage. September CPI, released on Wednesday 14 October, rose to 3.7% year on year from 3.4% in August, against expectations of about 3.6%, with the monthly gain of 0.6% in line. Core CPI came in at 2.6% against a 2.5% consensus, and 0.3% on the month against 0.2% expected. Petrol prices were the driver, up 9.1% in the month and 34.2% over the year, accounting for more than half the monthly increase.

Thursday's producer price index was worse. Final-demand PPI jumped 1.3% on the month against forecasts nearer 0.6%, taking the annual rate to 6.3%, the highest since 2022, with final-demand energy up 10.8% and responsible for over 80% of the rise. Core PPI excluding food, energy and trade services rose 0.5% on the month and 5.0% over the year. September retail sales rose 0.8%, but only 0.2% excluding petrol stations. Initial jobless claims came in at 199,000.

Treasury yields actually eased as the week went on, which is why Thursday's rotation worked at all: the Fed's own H.15 series shows the 10-year at 5.21% on 13 October, 5.19%, 5.10% and 5.09% by Friday, well off the 5.31% reached on 5 October. Gold rose to about $4,204 on Friday as yields and the dollar softened. Oil stayed the awkward variable — Brent held above $102 while an emergency reserve release knocked WTI lower.

Fed chair Kevin Warsh spoke at the IMF meetings in Bangkok on Friday, his last appearance before the blackout period began on 17 October, and deliberately gave nothing away: "I don't prejudge meetings. I don't believe in saying now what I might do at the meetings that we have in the balance of this year." He also described the path of AI development as likely to be "very bumpy". Futures had put the odds of an October hike at roughly 15% on Friday morning and trimmed them further afterwards. The Fed raised its target range to 3.75%–4.00% in September; Goldman Sachs reads the current signals as a pause this month.

Still to come

One convention worth knowing: US companies report quarterly rather than half-yearly and almost always release results outside market hours, so the share price reaction appears in after-hours trading and then at the next session's open. "Q3" means the three months to end-September for most, though Western Digital and others run fiscal years that do not match the calendar.

This article is for information and education only. It is not financial advice or a recommendation to buy, sell or hold any investment. Always do your own research.