S&P 500 Enters October Amid Weakened Market Breadth

The S&P 500 enters October, historically the third-best month for the SPDR S&P 500 ETF (SPY), following a September that saw a 0.26% gain. Despite the index's positive performance, market breadth has reached its lowest level since May 2025, with approximately 75% of S&P 500 stocks closing September lower. Gains were concentrated in a few large-cap technology and hardware companies, while sectors like banking and software faced declines as Treasury yields rose.