Stocks have reached their most expensive valuation in American history
Jeremy Grantham, one of the few investors whose warnings have repeatedly preceded genuine market catastrophe, now places the current American equity market at a valuation extreme without precedent in recorded financial history — surpassing even the dot-com fever, the housing bubble, and the speculative heights of the 1920s. The engine of this excess, he argues, is artificial intelligence: a technology whose promise has been real enough to inspire belief, but whose market impact has inflated stock prices far beyond what earnings or assets can justify. His counsel is not to rebalance or to hedge, but to leave — a rare and sobering instruction from a man who has earned the right to be heard.
- Grantham is not warning of a downturn — he is warning of a potential 70% collapse, a repricing so severe it would rank among the worst market events in modern history.
- AI enthusiasm has become a self-reinforcing spiral: each announcement lifts prices, drawing in more capital, which lifts them further — disconnecting valuations from any grounding in actual earnings or assets.
- Millions of ordinary investors — retirement accounts, pension funds, long-term portfolios — are concentrated in U.S. equities and may not realize how exposed they are to a historic reversal.
- Grantham's call is not to rotate or trim but to exit entirely, treating current elevated prices as a closing window rather than a new normal.
- The market has absorbed bubble warnings before and kept climbing — the unresolved question is whether AI's transformative potential is real enough to justify what investors have already priced in.
Jeremy Grantham has spent decades identifying inflated assets before they collapse, and his latest declaration is among the starkest he has ever made: U.S. stocks are now more expensive relative to their underlying earnings and assets than at any point in American financial history — more than the dot-com bubble, more than the 2007 housing euphoria, more than the Roaring Twenties.
The primary culprit, in his telling, is artificial intelligence. The promise of transformative AI has drawn enormous capital into equities, bidding prices to levels that bear little relationship to what companies actually produce or own. The dynamic has become self-reinforcing — each AI announcement lifts stocks, which attracts more money, which lifts them further still.
Grantham's concern is not abstract. He is warning of a potential 70 percent crash — not a correction, but a catastrophic repricing that would erase years of gains and force a reckoning with how far prices had drifted from reality. His message to investors is unambiguous: exit equities now, while prices remain elevated, rather than risk surrendering accumulated gains when the reversal comes.
What gives the warning its weight is its specificity. Grantham is not saying stocks are expensive in a general sense — he is making a measurable historical claim, one grounded in valuation metrics comparable across centuries of market data. Whether this moment proves to be the inflection point he believes it to be, or whether AI's economic impact ultimately justifies current prices, will determine whether his forecast becomes vindication or cautionary footnote.
Jeremy Grantham has seen a lot of market cycles. The legendary investor, whose firm manages billions and whose track record of spotting inflated assets spans decades, has now made a stark declaration: American stocks have reached their most expensive valuation in the nation's entire recorded history.
This is not a casual observation. Grantham is saying that even during the dot-com bubble of the late 1990s, even during the housing-fueled exuberance of 2007, even during the Roaring Twenties, stocks were not as expensive relative to their underlying earnings and assets as they are right now, in mid-2026. The current market, by his measure, has entered uncharted territory.
The warning comes with a specific culprit: artificial intelligence. Grantham points to the AI-driven enthusiasm that has gripped markets as a primary driver of this excess. Investors have poured money into equities on the promise of transformative AI technology, bidding up stock prices to levels that bear little relationship to what companies actually earn or own. The speculation has become self-reinforcing—each new AI announcement sends stocks higher, drawing in more capital, which sends them higher still.
Grantham's concern extends beyond mere overvaluation. He is warning of a potential 70 percent crash in stock prices. That is not a modest correction or a bear market in the conventional sense. It is a catastrophic repricing, the kind that wipes out years of gains and forces investors to reckon with how far removed prices had drifted from reality. Such a decline would rank among the most severe market events in modern history.
His message to investors is unambiguous: leave equities now, before the inevitable reversal. This is not a recommendation to rotate into different stocks or to trim positions gradually. It is a call to exit the market entirely while prices remain elevated, to avoid being caught when the bubble deflates. For those who have built wealth in recent years riding the AI enthusiasm, the implication is stark—the gains may prove temporary, and holding on could mean surrendering them entirely.
What makes Grantham's warning carry weight is not just his reputation but the specificity of his claim. He is not saying stocks are expensive. He is saying they are more expensive than at any point in American financial history. That is a measurable assertion, grounded in valuation metrics that can be compared across centuries of market data. It is also a prediction that carries real consequences for millions of people whose retirement savings, pension funds, and investment portfolios are concentrated in U.S. equities.
The market has heard warnings before. Bubble calls come regularly, and many prove premature. But Grantham has a track record of identifying genuine extremes. The question now is whether this moment represents the kind of inflection point he believes it to be, or whether the AI revolution will prove substantial enough to justify current valuations. The answer will determine whether his warning becomes a cautionary tale or a vindicated forecast.
Citas Notables
Grantham urges investors to flee U.S. equities before the market reprices— Jeremy Grantham's investment recommendation
La Conversación del Hearth Otra perspectiva de la historia
When Grantham says this is the most expensive market in American history, what exactly is he measuring?
He's looking at valuation ratios—price-to-earnings, price-to-book, market cap relative to GDP. The idea is that stocks are trading at multiples of their earnings that have no precedent, even going back to the 1920s.
But hasn't technology always commanded higher valuations? Why is this different?
Fair question. Tech companies have always been priced for growth. The difference now is the scale and the uniformity of it. The entire market is being lifted by AI enthusiasm, not just a sector. And the earnings haven't caught up to justify the prices yet.
A 70 percent crash—is that his base case or a worst-case scenario?
He's presenting it as a serious possibility, not a fringe outcome. When you have valuations this extreme, the math suggests that kind of repricing is what it would take to bring things back to historical norms.
What does he think happens to the economy if stocks fall that far?
He's focused on the market itself, but a crash of that magnitude would ripple through everything—retirement accounts, consumer confidence, credit availability. It's not just a stock market event.
Has he set a timeline for when this might happen?
Not explicitly in what we're seeing here. That's actually one of the hardest parts of bubble calls—you can be right about the direction and still be wrong about the timing. He could be early.
What would prove him wrong?
If AI actually delivers on the promises—if earnings growth accelerates enough to justify current prices. That's the bet the market is making right now.