Billionaire investor Jeremy Grantham: This is the most expensive market in American history

Summary

Jeremy Grantham argues the US stock market is the most expensive in American history, drawing parallels to the 2000 tech bubble, and predicts a 70% decline once it peaks. He also expects AI stocks to crash due to overinvestment, similar to past innovation cycles.

• Grantham defines bubbles using a statistical two-sigma deviation and notes all 26 historical ones eventually broke back to trend.
• He claims the current US equity market is the most expensive on record, with valuations far above long-term averages.
• He forecasts the market will peak sometime between now and two years, then drop by roughly 50-70%.
• The AI boom mirrors earlier revolutionary innovations like railroads and the internet, which triggered overinvestment and crashes.
• Grantham expects AI investors to 'lose their shirts' as the cycle repeats, despite AI's transformative potential.
• He highlights the uncertainty of timing but says the eventual collapse is inevitable.
• He cites Amazon's 92% decline in the 2000 bust as an example of how even eventual winners get crushed in a bubble.