Jeremy Grantham Calls U.S. Stock Market Most Expensive in American History

Jeremy Grantham has declared the U.S. stock market the most expensive in American history, with soaring valuations tied to artificial intelligence pushing prices to levels he regards as historically extreme. The assessment from the veteran investor adds a prominent skeptical voice to an equity rally that has drawn global capital into U.S.-listed technology names.

The AI Valuation Driver

Grantham's argument centers on the run-up in valuations surrounding artificial intelligence. His concern is not with the technology itself but with the price the market has assigned to the anticipated gains from it — a pattern he frames as the decisive factor in making this moment stand apart from prior peaks in U.S. market history.

The framing matters. Calling this the most expensive market in American history is a comparative claim that spans every prior bubble and cycle. It positions current AI-driven enthusiasm alongside, and above, past episodes of speculative excess in U.S. equities.

What "Most Expensive" Signals for Global Allocators

For international investors who route capital through U.S. equities, Grantham's characterization carries practical weight. When a market is priced at historically elevated levels relative to underlying fundamentals, the implied forward returns compress — a dynamic that affects pension funds, sovereign wealth vehicles, and cross-border allocators evaluating U.S. exposure against alternatives in other markets.

Grantham has a long record of identifying valuation extremes before they resolve, which gives his assessments an audience beyond the domestic market. His latest view will likely circulate among risk managers in Hong Kong, London, and Singapore who monitor U.S. positioning as a direct input into their own allocation decisions.

A Single-Cause Caution

It is worth noting that AI is doing a lot of explanatory work in Grantham's framing. Valuations across the U.S. market reflect many inputs — interest rate expectations, earnings revisions, index concentration, and passive fund flows among them. AI enthusiasm is a plausible accelerant, but attributing the entirety of a historic valuation extreme to one theme invites scrutiny. Whether the market resolves that extreme through a correction or through earnings growth that eventually justifies the prices is the question Grantham's warning leaves open.

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