The S&P 500 Has Fallen in 56% of Septembers Since 1928. Here's What That Means for Artificial Intelligence (AI) Stocks.

The seasonal tape argument is weak by itself; what matters is that September often concentrates flows from tax-loss harvesting, quarter-end de-risking, and macro-event hedging. In a crowded AI trade, that can create temporary multiple compression even when the fundamental slope is still up, so the first-order move is more about positioning than operating deterioration.

NVDA remains the higher-quality duration asset in the group: its upside is less about another earnings beat and more about whether hyperscaler capex keeps extending into 2026. The bigger near-term risk is not demand collapse but a rates-led de-rating if inflation stays sticky after the Fed meeting; that would hit the entire AI basket before it changes any revenue trajectory.

MU is the more tactical name because memory is a cleaner read-through on whether AI infrastructure spend is broadening beyond accelerators into HBM and server build-outs. That also makes it more fragile on the downside: if pricing or mix disappoints into the Sept. 23 print, the stock can re-rate much faster than NVDA. The contrarian point is that the market may be underestimating how quickly MU can turn from beneficiary to tell on AI digestion, while overestimating the predictive power of a calendar effect that is historically small.