S&P 500’s 15 largest stocks now hold a record 46.7% of the index

A handful of AI-fueled mega-caps now control nearly half of America's benchmark index, raising fresh questions about what passive investors actually own The S&P 500’s 15 largest stocks now account for a record 46.7% of its total market value. That matters because the S&P 500 is the default holding for retirement accounts, index funds and anyone told to “just buy the market.” Increasingly, buying the market means buying a small cluster of tech giants. The concentration figure is approximately 46.7% as of mid-to-late October 2026, according to the research findings. Technology sector exposure across the index sits close to 46%.

Source: Crypto Briefing