Retail investors' net purchases of U.S. stocks reached $9.1 billion last week, setting a 15-year record, with capital concentrated in the AI sector.

Scott Rubner, Head of Equity and Derivatives Strategy at Citadel Securities, noted in a recent research report that retail investors net purchased $9.1 billion in U.S. stocks through the firm's platform last week, marking the largest single-week net buy record in nearly 15 years. The heavy concentration of funds in artificial intelligence (AI)-related stocks and exchange-traded funds (ETFs) pushed the Nasdaq 100 Index and S&P 500 Index to record highs.