The AI boom: rational enthusiasm or the next dot-com bubble?

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Malin Andersson<br>Senior Team Lead - Economist · Economics, Business Cycle Analysis

Johannes Breckenfelder<br>Senior Economist · Research, Financial Research

Stefano Corradin<br>Team Lead - Economist · Research, Financial Research

Kalin Nikolov<br>Head of Section · Research, Financial Research

Maria Antonietta Viola<br>Research Analyst · Research, Financial Research

THE ECB BLOG<br>The AI boom: rational enthusiasm or the next dot-com bubble?

17 August 2026<br>By Malin Andersson, Johannes Breckenfelder, Stefano Corradin, Kalin Nikolov and Maria Antonietta Viola<br>The rise of AI has driven a blistering rally in the tech sector, bringing stock market valuations to levels last seen during the dot-com bubble. Although AI is reshaping the economy, do today’s high valuations bear the risk of an abrupt and painful setback in the euro area?

Valuations on the US stock market, as measured by the CAPE ratio, are currently close to their historical peak.[1] Euro area equity valuations have also risen, albeit to a lesser extent (Chart 1). Markets on both sides of the Atlantic reflect investors’ enthusiasm about artificial intelligence (AI) shaping the economy and driving profits. The extremely optimistic valuations raise questions: do today’s stock market prices reflect a rational bet on the transformative technology? Or are we seeing a remake of the dot-com bubble? We argue that economic research on past technological revolutions points to a worrisome conclusion: a correction of current stock market valuations is likely.<br>A sharp stock market correction would have severe consequences for the euro area, through two channels. One is euro area investors’ direct exposure to the Magnificent Seven stocks (hereafter Mag7) and the other is the degree of overexuberance in euro area stock markets themselves.[2] This post explains why a correction should be expected even if current valuations are rational, why that matters not only to the shareholders who would take the direct hit, and what it implies for the euro area specifically.<br>Chart 1<br>US and euro area stock market valuations<br>a) S&P 500 Index (cyclically adjusted price-to-earnings ratio)<br>b) Euro area Market Equity Index (cyclically adjusted price-to-earnings ratio)<br>(Index)<br>(Index)

Source: Datastream<br>Notes: Price-earnings ratio (monthly) from 1980 to 2026. Numerator: real (inflation-corrected) S&P Composite Stock Price Index (panel a) and Euro Stoxx 50 Price Index (panel b). Denominator: moving average over preceding ten years of real S&P Composite (panel a) and Market Equity (panel b) earnings.

Why do technological revolutions so often end in a boom and bust?<br>The current excitement surrounding AI has many historical precedents. To name just a few: the railway boom of the 19th century, the expansion of electricity and radio in the 1920s and the surge of the internet, or the “dot-com era”, in the 1990s. In each case, a genuinely transformative technology attracted investment, and the stock market valuations of firms that adopted it rose strongly before falling sharply. Economic research offers two complementary explanations.<br>First, the rational view argues that high valuations can be justified by extreme uncertainty about a new technology’s productivity.[3] Why has Nvidia’s share price risen 20-fold since 2022? Because investors rationally perceived that the company would become the next Google – with a highly uncertain and potentially large upside. In the worst case in such a scenario, investors lose their investment. But in the best case, the gains are large and genuinely hard to bound. This “option value” increases the stock valuations of early adopters, causing their price-to-earnings ratios to rise sharply.<br>Even if the technology succeeds, stock prices may eventually fall. Why? The nature of uncertainty shifts from a “single sector” to the “entire” economy. Initially, the new technology is like a small-scale experiment. If it fails, it’s unfortunate for that company, but the rest of the economy is unaffected. The risk can be diversified away. As adoption spreads, the same uncertainty becomes economy wide. If something then goes wrong with that technology, the whole economy suffers. This risk cannot be diversified, so investors demand a higher risk premium. However, this does not necessarily mean that profits will fall. Adoption itself is good news for cash flows, but the rising risk premium has the opposite effect and tends to prevail historically (Chart 2, blue line), unless profit growth is strong enough to compensate for that (Chart 2, yellow line). The exact timing is unknowable in...