Full Breakdown
Jeremy Grantham Warns AI-Driven Stock Market Bubble Is at Historic Levels
6/26/2026, 11:15:10 PM
AI-Fueled Stock Market Valuation Hits Record Levels
Veteran investor Jeremy Grantham, co-founder of Boston-based GMO, told CNBC’s “Squawk Box” that the surge in artificial-intelligence-related equities has pushed the U.S. equity market to a valuation unprecedented in American history. He cited a market-capitalization-to-GDP ratio of roughly 235 %, indicating that the total value of U.S. listed stocks now exceeds twice the size of the nation’s economy.
Historical Context and Valuation Metrics
Grantham referenced the “Buffett indicator,” a metric Warren Buffett has used to warn when markets become overheated. Buffett famously said that when the ratio approaches 200 %—as it did in 1999-2000—investors are “playing with fire.” Grantham noted that the current ratio surpasses that level and likened the situation to past bubbles, including the 1999 internet bubble, the South Sea Bubble, and the 2007-2008 housing crash, all of which were preceded by “excessive enthusiasm, over-investment and significant destruction of value.”
Grantham’s Forecast and Investment Guidance
Grantham warned that the AI-driven rally could culminate in a “major correction,” estimating that some AI-linked stocks may fall up to 70 %. He emphasized that the timing is “terribly uncertain” but that markets could “potentially peak.” To mitigate risk, he advised investors to reallocate about 60 % of their portfolios to non-U.S. equities (including Europe, Japan, Canada, Australia and emerging markets), place 5-10 % in precious metals, and hold the remainder in short-term government bonds, real estate, or similar low-volatility assets. He explicitly rejected the S&P 500 as a current investment choice.
Data & Statistics
- Market-cap-to-GDP ratio: ~235 % (Longtermtrends.com).
- U.S. equity earnings multiples: 35-40 ×, well above historical averages.
- Emerging-market indices: +65 % over the past 12 months, versus +25 % for the S&P 500.
- GMO’s managed assets: ? $85 billion.
- Grantham’s prior 2024 warning: “The long-run prospects for the broad U.S. stock market here look as poor as almost any other time in history,” yet equities continued to rise afterward.
Conflicting Reports & Gaps
Grantham’s March 2024 outlook predicted a bleak long-run outlook for U.S. stocks, but market indices advanced in the months that followed, illustrating uncertainty about the precise timing of any correction. No independent forecasts or counter-arguments appear in the provided sources.
Verbatim Quotes
- “Based on the value of the stock market compared to GDP, with modifications, this is the most expensive market in American history,” — Jeremy Grantham, Investor
- “The long-run prospects for the broad U.S. stock market here look as poor as almost any other time in history,” — Jeremy Grantham
- “As he states, he has never bought Bitcoin and does not intend to invest in it in the future, considering that it lacks real economic fundamentals and practical utility.” — Jeremy Grantham
- “Buy a broad-based index of non-US equities.” — Jeremy Grantham
- “approaches 200% — as it did in 1999 and a part of 2000 — you are playing with fire.” — Warren Buffett, Investor (cited by Grantham)
- “No.” — Jeremy Grantham, in response to investing in the S&P 500
What’s Next
Grantham expects a potential market correction driven by AI-related overvaluation. He recommends that investors begin shifting assets toward international equities, precious metals, bonds and real-estate holdings while avoiding U.S. growth stocks and cryptocurrencies. Monitoring the market-cap-to-GDP ratio and earnings multiples will be central to assessing whether the bubble is inflating further or beginning to deflate.
