October's pullback in US AI-related tech stocks is putting the market's favorite coping strategy to the test: keeping the S&P 500 steady by rotating into other sectors, even though technology now makes up a hefty 38% of the index. For months, investors have leaned on this rotation to cushion the blow whenever mega-cap tech wobbles. But recent weakness in some of the biggest names is raising questions about how long that cushion can hold.
What's driving the selloff?
Reuters reports that softer results from Alphabet, Amazon, and Intel have revived doubts about the AI boom. The core worry is simple: building out data centers and chips requires enormous upfront spending, and investors are increasingly asking when that outlay will turn into reliable profits. Hyperscalers—the giant cloud and data-center operators—have been the primary engine of demand for semiconductors and infrastructure, so any sign they might pull back on capital expenditures sends ripples through the entire tech supply chain.
Until recently, the damage looked contained. The S&P 500's tech sector fell 6.8% in October, but nine of the index's 11 sectors still rose, leaving the overall benchmark down less than 1% for the month. That pattern—tech down, everything else up—was exactly the rotation investors had hoped for. It suggested the market could digest AI jitters without dragging the whole index down.
Friday's break: a warning sign
Friday showed how fast that "contained" story can break. Tech dropped 4.2%, with Intel sinking almost 29% after its disappointing outlook. The S&P 500 fell 1.8%, and the index closed below its 100-day moving average for the first time since April. That technical level matters because many investors treat widely watched trendlines as risk checkpoints. When an index slips through a level that lots of people track, some automated strategies automatically dial down risk, and some discretionary managers get more defensive. That can shift flows from "rotate within stocks" to "raise cash," which tends to pull down even sectors that were holding up.
Strategist Matthew Maley told Reuters that previous meaningful breaks below this trendline were followed by further declines in the weeks that followed. And because tech is 38% of the S&P 500, a selloff in a handful of mega-cap names can drag the whole benchmark through these technical tripwires, even if the rest of the market looks healthier.
What it means for investors
For everyday investors, the key takeaway is that the market's safety net may be wearing thin. The rotation strategy—moving money from tech into other sectors like financials, industrials, or consumer staples—has worked for a while, but it has limits. If the biggest tech stocks keep falling, they can pull the entire index down with them, regardless of how well other sectors are doing.
This is also a reminder that the AI trade is not a one-way bet. The enormous capital spending on data centers and chips is a bet on future demand, but it carries real risk. If hyperscalers meaningfully rein in their spending, the impact would be felt across semiconductors, networking equipment, and data-center construction—sectors that have been big winners this year.
Investors should watch for further weakness in tech and any signs that the rotation is failing. A break below the 100-day moving average is not a guarantee of a crash, but it is a signal that the market's internal defenses are being tested. As always, diversification and a long-term perspective remain the best tools for weathering these swings.
For more on how AI demand is shaping markets, see our coverage of South Korean stocks rebounding on AI chip demand and the Deutsche Bank view that the AI selloff is overdone.
