Retail investors net purchased $9.1 billion in US stocks last week, marking the largest weekly inflow in 15 weeks as both the Nasdaq 100 and S&P 500 reached record highs. According to Citadel Securities, capital primarily targeted AI-related assets, with semiconductor stocks attracting $2.6 billion in net buying—the third-highest weekly total in a year—and AI infrastructure stocks drawing approximately $2.4 billion. The surge reflects heightened bullish conviction rather than increased trading volume. Retail buying exceeded selling by 2.7%, placing the directional bias indicator near the 90th percentile for the past year, while overall trading activity remained at just the 42nd percentile. October semiconductor net buying is now tracking toward a potential single-month record since platform records began.