S&P 500 excluding AI stocks leads broader index in October reversal

The S&P 500 excluding artificial intelligence stocks has outperformed the broader index by 6.4 percentage points so far in October, putting it on track for its strongest relative monthly performance on record, according to figures shared in a market update.

The shift marks a sharp reversal from September, when the index excluding AI stocks underperformed the S&P 500 by 5.1 percentage points, described in the update as the second-worst relative performance on record.

The October gap has widened in recent weeks. Over the past three weeks, the S&P 500 excluding AI stocks has outperformed the broader index by 7.4 percentage points, which the update identifies as the widest three-week spread on record.

The previous largest monthly outperformance cited was 3.6 percentage points in July.

Performance has been volatile throughout 2026. According to the figures, the index excluding AI stocks has outperformed the S&P 500 in four months this year, while the broader index has led in six.

The update attributes the latest shift to investors taking profits from AI-related investments. However, the figures alone do not establish whether profit-taking is the main cause of the change, or whether other sectors and market factors have contributed.

The comparison also depends on how the AI-stock group is defined and which companies are excluded from the calculation. The figures shared did not specify the methodology or provide details of the stocks included in the AI category.

The data point to a change in relative market performance, but do not by themselves establish whether the shift will continue through the rest of October or beyond.