S&P 500 falls 1.2% as AI stocks sink but over 300 constituents gain

The headline drop masks unusual breadth: most S&P 500 names rose even as the index had its worst day since July, and small caps and the Dow held up — a sign the selling was concentrated in AI and semiconductor leadership rather than broad risk-off. That concentration cuts both ways: it shows how much index-level direction now depends on a narrow AI trade, and it offers a reminder that cap-weighted benchmarks can look weak while most constituents are fine. Whether this divergence is a one-day rotation or the start of a wider unwinding in AI leadership is the open question worth tracking.