S&P 500's AI-Driven Rally Raises Concerns About Market Risk

The US stock market has hit record levels in 2026, with the S&P 500, Nasdaq Composite, and Dow Jones Industrial Average gaining more than 20% over the past 12 months.

A major factor behind this strong market rally is the rapid growth of artificial intelligence (AI) stocks, particularly Nvidia, Apple, Microsoft, Amazon, and Alphabet.

However, this AI boom has raised concerns about a possible AI bubble. Bank of America's Global Fund Manager Survey found that fund managers see an AI bubble as the biggest tail risk facing the market right now.

The S&P 500 is unusually dependent on a small group of mega-cap technology companies, with the top 10 companies making up around 40% of the index. This level of concentration is similar to the 1965 level and even higher than during the dot-com bubble in March 2000.

The high concentration of these large companies means that a sharp decline in their shares could put pressure on the entire S&P 500. Investors may face greater market risk, despite strong returns for smaller companies.