S&P 500, Nasdaq Post Worst Day Since July as AI Stocks Tumble on Hot CPI

On October 14, 2026, the S&P 500 dropped 1.1% and the Nasdaq composite fell 1.9%, marking the worst day for both indexes since July. The decline was led by AI-related stocks after a hotter-than-expected September Consumer Price Index report. The CPI rose 0.6% month-over-month and 3.7% year-over-year, topping the 3.6% consensus estimate.

The inflation reading renewed concerns that the Federal Reserve might raise interest rates. Higher rates are particularly damaging for companies that require large upfront capital and wait years for returns, a description that fits AI infrastructure. Building data centers and purchasing chips at scale demands heavy borrowing, making these firms vulnerable to rising financing costs.

The selloff hit AI buildout names hard. Nvidia and Broadcom each lost 3.7%, while Advanced Micro Devices fell 6.1% — nearly double the drop of its larger rival. CoreWeave suffered the worst decline, plunging as much as 15.9%. The Philadelphia Semiconductor Index, or SOX, extended its losing streak, indicating broad weakness across chip stocks rather than isolated declines.

Rising Treasury yields added to the pressure, as higher yields make borrowing more expensive and put AI infrastructure firms under sharper scrutiny regarding how they will fund expansion. According to Crypto Briefing, the market was already nervous before the CPI report, having been rattled by negative reports about OpenAI's revenue projections and commentary comparing AI investment to 'casino gambling.'

The immediate takeaway is that the AI trade is now tightly tied to macroeconomic data. A single inflation print moved chip stocks more than the broader market, highlighting the rate sensitivity embedded in these valuations. The Nasdaq's heavier tech exposure resulted in a 1.9% drop versus the S&P 500's 1.1%, and within tech, AMD and CoreWeave fell further than Nvidia and Broadcom.

The re-evaluation of aggressive AI valuations had already begun before the CPI report, but the inflation data accelerated it, turning a gradual reassessment into a sharp one-day repricing. The spread between the indexes underscores how much the AI trade depends on the rate outlook.