A trader works on the floor of the New York Stock Exchange during morning trading on August 13, 2025 in New York.ANGELA WEISS/AFP via Getty Images AI optimism is driving the S&P 500 price-to-book ratio to records, surpassing dot-com levels. High valuations reflect expectations for AI-driven earnings. While the ratio's level is head-turning, it doesn't necessitate that stocks are in a bubble. Stock-market bulls convinced of the power of AI to transform the economy often shrug off comparisons to the ...