Based solely on the article, the valuation of US stocks has entered an extreme range, but analysts believe high valuation alone is not enough to end the current bull market. The real "culprit" requires a significant jump in interest rates or a fundamental collapse of the AI profit logic, neither of which has been met at present. Ian Harnett, co-founder and chief investment strategist of Absolute Strategy Research, wrote that since October 2022, the cumulative increase of US stocks has exceeded 100%. The core driving forces are strong corporate profits driven by AI technology and a relatively loose monetary policy environment. The current price-to-earnings ratio based on actual earnings in the past 12 months is 28.4 times, about 40% higher than the average of the past 40 years. Based on cyclically adjusted 10-year average earnings, the price-to-earnings ratio is 41 times. Harnett noted that such extreme valuation has only appeared near the top of major bull markets in history, but to break the current momentum, a major change is needed in interest rate expectations, corporate profit prospects, or the fundamentals of the AI sector. He stated that what really causes market turmoil is the speed and magnitude of interest rate changes, noting that market reversals in 1907, 1929, 1973, and 2000 all occurred after policy interest rate changes.