Average S&P 500 Stock Just Pulled Off Its Biggest Reversal on Record

The average S&P 500 stock is outperforming the cap-weighted index by 4.1 percentage points in October — the biggest reversal of fortune on record, according to preliminary numbers from Dow Jones Market Data. That swing follows a September in which the equal-weight index lagged its cap-weighted sibling by 4.5 points, so the typical stock has round-tripped from historic pain to historic gain in roughly six weeks.

The driver is the wobble in the artificial-intelligence trade. The tech-heavy Nasdaq Composite was down just 1.4% for the month as of Tuesday, but the damage concentrated where the AI trade lives: chips and the so-called hyperscalers. The PHLX Semiconductor Index has dropped more than 10% in October. Shares of Nvidia, Alphabet and Meta Platforms — three of the most valuable publicly traded companies in the world — have all been hit hard.

What's actually breaking the trade?

Bond markets, not earnings. Rising yields pressured stocks through September, and by October the stress reached the AI complex through an unexpected channel: debt issued by neoclouds like CoreWeave sold off. Investors began asking whether rising borrowing costs could cap the prolific amounts of AI-related spending that have powered the trade.

"People started to worry that the debt markets were telling you something — that you can't fund AI this way," said Ayako Yoshioka, senior investment strategist at Wealth Enhancement, a large independent RIA. "That just shows you that we're short of capital. The actual bottleneck is there."

That's a shift worth noticing. For two years, the constraint on AI infrastructure was assumed to be chips and power. Yoshioka's read says the binding constraint may now be financing itself — a very different problem, and one that hits capital-hungry neoclouds first.

What does this change for the average stock?

Plenty. In September, only one of the S&P 500's 11 sectors finished higher: information technology. Everything else — struggling software names, consumer staples, stodgy healthcare firms — sold off as investors scrambled for the perceived safety of Big Tech. October has handed those unloved groups a reprieve.

The equal-weight index is the cleanest barometer of that shift because it puts the smallest S&P 500 component on par with giants like Nvidia. When it beats the cap-weighted version by four-plus points in a single month, breadth has genuinely returned — money is rotating out of a handful of mega-caps and into the other 490-odd names.

Is the AI trade over?

Probably not, and the market itself said as much this week. The Nasdaq rallied after Anthropic released its pre-IPO financials on Monday and kept climbing Tuesday. The filing appears to have allayed some of the debt-market concerns, at least for now — if a leading AI lab's numbers hold up, the funding math looks less fragile than the necloud bond selloff implied.

The takeaway for practitioners is a two-sided one. The record reversal shows how quickly concentrated trades unwind when financing costs move against them — September's safe haven became October's stretcher case in a matter of weeks. But the Anthropic rally shows sentiment can snap back just as fast. Watch the bond desks, not just the chipmakers: the next leg of this rotation, in either direction, likely gets its signal from how cheaply AI's biggest spenders can still borrow.