The average stock is having its best relative performance in decades as the AI trade falters

The equal-weighted S&P 500 rose 4.9% in October while the market-cap-weighted index fell 0.9%, a 5.8-percentage-point divergence and the equal-weighted index’s strongest relative month since April 2009, according to Bespoke. The article links the benchmark’s decline to concerns about the sustainability of the AI trade and rising oil prices amid U.S.-Iran tensions; technology represents 37% of S&P 500 market capitalization. Bespoke cited historical median gains of 4.6% three months and nearly 13% one year after the market-cap-weighted index lags, while Fundstrat’s Tom Lee said the S&P 500 could top 8,200 by year-end, versus Friday’s close of 7,580.07.

Analysis

The key signal is a divergence in market breadth, not proof that AI leadership has broken. If participation continues to widen, earnings upgrades and incremental flows can support the median stock even while mega-cap concentration keeps the cap-weighted index vulnerable to a few valuation resets. Conversely, a rebound in AI leaders could make the cap-weighted index outperform again without confirming broader economic strength. The cited historical pattern is not a reliable timing rule: past absolute gains after relative underperformance do not establish that equal weight will keep leading, and the sample may reflect very different rate and earnings regimes.

For the next 1–3 months, watch whether breadth persists through earnings revisions and whether the equal-weight/cap-weight relative trend holds; a reversal would suggest October was rotation rather than durable broadening. Over 6–18 months, sustained diffusion of AI investment beyond infrastructure leaders could broaden beneficiaries, but oil-driven inflation or higher rates would pressure the more cyclical and smaller constituents that underpin an equal-weight trade. The main contrarian risk is treating a striking one-month relative move as a structural regime change before confirming it in forward earnings and market leadership.

Key Decisions for Investors

• Prefer a conditional, modest long equal-weight S&P 500 / short cap-weighted S&P 500 pair (e.g., RSP versus SPY), entered on consolidation rather than chasing October’s move. This isolates a breadth view better than an outright index short; size for residual sector and beta differences.
• Falsify or exit the breadth position if the RSP/SPY relative line gives back its October advance, or if earnings-revision breadth narrows back to a small group of mega-cap names. Track both relative price action and estimate revisions rather than relying on the historical average cited in the article.
• Avoid interpreting cap-weight index weakness alone as a broad-market deterioration. Keep net exposure controlled: the pair can lose if AI leaders rebound sharply, while an oil shock or renewed rate pressure could also hurt equal-weight constituents disproportionately.
• Watch crude and U.S.–Iran developments as a near-term cross-current. A sustained oil rise would weaken the broadening thesis through inflation, rates, and cost exposure; absent confirmation in earnings breadth, there may be no compelling outright directional trade.