Passive investing is no longer diversified. The S&P 500 is now over 50% weighted towards AI and big tech, with the top five companies alone comprising 30% of the index. Many investors unknowingly double down on this risk by holding an index fund while also buying the same stocks individually.

Due to the market cap concentration of a few "Magnificent 10" tech companies, owning an S&P 500 index fund is no longer a truly diversified position. Investors, especially those nearing retirement, must add geographic diversification (e.g., international stocks) to protect against a potential drawdown in US tech valuations.

Despite its name, the S&P 500 is no longer a diversified bet on the US economy. A mere 10 AI-related stocks drove 72% of all gains, meaning investors are unknowingly making a highly concentrated bet on a single, expensive, and crowded sector.

Traditionally viewed as diversified, index funds like the S&P 500 have become concentrated wagers on AI. The top 10 companies, nearly all driven by AI, now make up over 40% of the index's value. This means passive investors are taking on significant, non-obvious, sector-specific risk.

With a few AI-related stocks now 40% of the S&P 500, passive investing no longer offers broad diversification. Investors believe they are buying the market but are actually making a massive, concentrated bet on a single technology theme, which undermines the core safety premise of index funds.

The original purpose of buying an S&P 500 index fund was diversification. With the 'Magnificent 10' tech companies now comprising nearly 40% of the index's value, it has morphed into a highly concentrated investment in a single sector, undermining its role as a broad market proxy.

Due to the dominance of a few tech "hyperscalers," the S&P 500 is now heavily concentrated, with the top 10 stocks comprising 40% of the index. Investors who believe they are buying a diversified market basket are unknowingly making a large, concentrated bet on a handful of growth companies.

Investing in the S&P 500 is no longer a path to broad market diversification. With the top 10 tech companies comprising 40% of the index, it functions more like a sector-specific fund. True diversification now requires looking at other regions and asset classes.

The S&P 500 is less diversified than many believe. The top 7 tech companies now make up 32% of the index's value, more than double the historical peak of 17% for any group of companies. This creates significant concentration risk in a supposedly broad-market fund.