Historic warning signals reappear: Schiller PE ratio of US stocks approaching 2000 peak. "Hindenburg Omen" also shines light on the NYSE and Nasdaq.

This week, two market signals that are significant enough to be recorded in financial history are both flashing red lights at the same time. The US stock market is experiencing an extremely rare dual extreme state in terms of valuation and technology: on the valuation side, the Shiller cyclically adjusted price-to-earnings ratio (CAPE Ratio) developed by Nobel laureate Robert Shiller has surged to 42.32, just under 5% below the peak value during the 2000 dot-com bubble period. On the technology side, a rare technical warning signal, the "Hindenburg Omen", has been triggered simultaneously on the New York Stock Exchange and Nasdaq, sparking intense debate among traders about whether the prosperity of the US stock market is becoming increasingly fragile beneath the surface. Both signals themselves are significant, but more importantly, they point to the same underlying issue: underneath the facade of the stock indices continually reaching new highs, the participation in the rise may be rapidly narrowing, with the frenzy of a few giants masking the weakness of most stocks. Shiller P/E ratio "red alert": the third extreme value in history The cyclically adjusted price-to-earnings ratio (CAPE), developed by Robert Shiller, compares the current stock price with the average earnings over the past ten years adjusted for inflation to smooth out the interference of economic cycles on earnings. It is considered one of the most reliable indicators of long-term stock market valuation levels. As of May 2026, this indicator has risen to 42.32, just under 5% below the peak value reached during the dot-com bubble period. If stock prices further exceed this previous high point, it will set a new record for the highest valuation level in US stock market history. The warning significance of high CAPE levels from a historical perspective is self-evident: historically, the CAPE ratio has fluctuated around a long-term average of about 17. The current reading of 42.32 means that the valuation of the US stock market has surpassed most periods leading up to the global financial crisis, the rebound after the pandemic, and even the majority of the period of excitement during the dot-com bubble in 1999. Historically, this indicator has only reached similar or even higher extreme levels in two periods: on the eve of the Great Depression in 1929 and on the eve of the bursting of the dot-com bubble in 2000. Each major collapse has started with a sharp rise in the Shiller P/E ratio. Concurrently soaring with valuation, market concentration has also increased. Currently, the top ten components of the S&P 500 Index account for over 40% of the total market value, nearly 50% higher than the level of about 27% during the dot-com bubble period in 2000. Tech giants such as NVIDIA (with a market value exceeding 5.7 trillion US dollars), Apple, and Microsoft have contributed the vast majority of the index's gains, demonstrating a highly structural feature of reliance on a small number of stocks. Ben Snider, the new chief US equity strategist at Goldman Sachs, pointed out in a year-beginning outlook report that the combination of "high valuations, extreme concentration, and strong recent returns" in the US stock market bears a striking resemblance structurally to market rallies following overheating in the 20th century. Hindenburg Omen: "cracks" under the facade of prosperity, flashing simultaneously on NYSE and Nasdaq While the valuation signal is flashing red, another more "mysterious" technical warning signal is quietly being triggered within the market. The "Hindenburg Omen" is a technical indicator named after the Hindenburg airship disaster in 1937, and its core logic is not to predict the direction of the index, but to detect "divergence" within the marketwhen many stocks simultaneously establish new highs and new lows, it signifies a serious differentiation within the market: while some stocks continue to rise strongly, others are quietly collapsing. Even though major indices such as the S&P 500 and Nasdaq 100 remain at high levels, the simultaneous occurrence of new highs and new lows indicates a weakening market breadth and rising uncertainty. The triggering of this indicator has garnered widespread attention on Wall Street, especially due to its simultaneous confirmation by two major exchangesan extremely rare occurrence during a period of strong upward movement in the indices. Historically, the Hindenburg Omen has appeared before major market corrections, including the stock market crash of 1987, the burst of the dot-com bubble, and the financial crisis of 2008. In February 2026, this signal was triggered three times within six days, and over the past six months, there have been eight clusters of signals, leading analysts to warn that "signal clusters often indicate the formation of market tops." As we enter May, the internal structure of the market continues to deteriorate. According to the latest data, while the S&P 500 Index has been frequently setting new highs, the divergence between the number of stocks reaching new highs and lows on the New York Stock Exchange continues to widen, with funds highly concentrated in a few large-cap stocks, leading to a significant decline in overall market participation. The Goldman Sachs Chief US Equity Strategist team warned in their latest report that the current upward trend in US stocks is highly concentrated in a few giant tech stocks, with market breadth falling to levels not seen since the dot-com bubble period, and downside risks are continuing to accumulate. However, traders also caution that this signal itself may be prone to false alarms, as a single trigger does not guarantee that a market crash is imminent. Technical analysts typically look for further confirmation signals in the following trading days to assess the validity of this omen. Strong earnings and AI faith: why the bulls are still holding on Despite both valuation and technical indicators sounding warnings, the US stock indices continue to hit new record highs. As of May 15th, the S&P 500 Index closed at 7,501.24, the Nasdaq Composite Index closed at 26,635.22, both setting new intraday and closing highs. The Dow Jones Industrial Average surged over 370 points on the same day, recovering and stabilizing above the 50,000 point mark. The core logic supporting the bulls lies in the fundamental differences between this market cycle and the 2000 bubble period. The leading AI companies in this cycle have strong profitability. The overall forward price-to-earnings ratio of the technology sector is around 30 times, much lower than the over 50 times seen during the dot-com bubble period. AI core beneficiaries such as NVIDIA, Google, and Microsoft have ample cash flow and real profit growth, in stark contrast to the mass speculation in the dot-com era involving "profitless, revenueless, and productless" internet companies. In addition, recent overall corporate earnings have been strong, providing an important fundamental support for the market. Morgan Stanley's Chief Strategy Officer Wilson believes that, with the economic restructuring and profit growth support, the US stock market is breaking free from its reliance on rate cuts, as long as inflation is demand-driven rather than cost-driven, and does not trigger a new round of rate hikes. The increase in pricing power is actually a significant positive for the stock market, and he has raised the year-end target for the S&P 500 to 8,000 points. Key divergence: bubble or not, will ultimately depend on the realization of the "trillion-dollar bet" The core disagreement surrounding whether the US stock market is in a bubble will ultimately depend on a key variable: whether the annual AI capital spending of over $700 billion can be translated into sustainable profit growth. A Deutsche Bank survey shows that 57% of institutional investors view the revaluation of AI as the biggest market risk at present. A group of well-known investors led by Michael Burry, the prototype of the character in the movie "The Big Short," has issued stern warnings. Burry estimates that the current price-to-earnings ratio of the Nasdaq 100 Index is as high as 43 times, significantly higher than the reasonable implicit level of around 30 times, suggesting that "Wall Street may have overestimated the earnings level of the fastest-growing, highest-valued batch of leading companies by over 50%." He wrote, "We are witnessing history. But in the stock market, this is not a good thing." He likened the current market to "the thrilling moment just before a devastating car crash." Economist Zeberg also warned that the market is experiencing the largest bubble in history and predicts a more severe recession than in 2008. Based on his Buffett Indicator (the total market value of US stocks as a percentage of GDP) nearing 230%, far exceeding the peak during the dot-com bubble period, by about 75% above the long-term trend. Not all pessimistic voices come from the "short camp." Morgan Stanley strategist Wilson, once regarded as the most famous "Big Short" on Wall Street, is now on the bullish side. He believes that the market's previous adjustment was not "blindly optimistic," but a profound self-correctionabout half of the components in the Russell 3000 Index have experienced wide swings of over 20%, and the forward P/E ratio of the S&P 500 has compressed by 18% from its peak. "The market doesn't truly need a rate cut to sustain the rally," as long as profit growth remains strong, there is still upside potential for the indices. Furthermore, HSBC Global Investment Research raised its year-end target for the S&P from 7,500 to 7,650 on May 11, and synchronized its EPS growth forecast for the year by 8% to $325 per share, with an expected growth rate of around 20%. Strategist Nicole Inui outlined four progressive catalysts in the report: tech stock revaluation (which can contribute 300-700 points), lagging sectors catching up (which can contribute 130 points), AI efficiency improvement (which can contribute 200 points), and ideal rate scenario (which can contribute 300 points). The team led by Citi Group strategist Beata Manthey also maintained an "overweight" position on US stocks in their latest global strategy allocation report, while highlighting three major sectors in technology, healthcare, and materials. Manthey explicitly stated in the report, "The 'trend of concentration' within the market will continue to exist, and with the spillover effects from the Iran conflict, fundamental factors will once again take the lead." Federal Reserve transition and policy uncertainty: new variables at the macro level At the macro level, the Federal Reserve is in a sensitive transition period. The term of current Chairman Powell officially ended on May 15, with Kevin Warsh being approved as the new chairman by a vote of 54 to 45 in the Senate. The April FOMC meeting resulted in an 8:4 vote to keep the federal funds rate unchanged at 3.50% to 3.75%, showing a rare voting divide since 1992, with significant internal disagreements about the future direction of policy. According to the CME's "FedWatch" tool, the market expects a probability of over 98% that rates will stay unchanged until July and a high probability of remaining cautious throughout the year. After Warsh takes office, there is a high expectation in the market for a near-term inclination towards rate cutshe favors a "trimmed mean PCE" inflation indicator that is low, and rate cuts align with the political demands of the Trump administration. However, with stalled US-Iran talks, high international oil prices, coupled with internal divisions within the Federal Reserve, consolidating opinions and pushing for rate cuts rapidly may prove difficult for the new chairman. The CPI and PPI data released this week have both exceeded expectations, showing that energy costs are translating into consumer-side inflation. It is worth noting that even with rate cuts in motion, there are uncertainties in the policy transmission path. The current size of the Federal Reserve balance sheet is about $6.75 trillion, and if rate cuts and balance sheet reductions were to proceed simultaneously, "the negative effects of tapering may significantly outweigh the positive liquidity release from rate cuts, causing index-level fluctuations of 10% in the stock market." Summary Combining the peak of the Shiller P/E ratio, the triggering of the Hindenburg Omen, the rise in earnings concentration, and the transition of Federal Reserve power, the current challenges facing US stocks are not just a single signal of a bubble, but a resonance of three dimensions: valuation, structure, and policy. The core difference from the dot-com bubble in 2000 lies in the fact that the technology companies back then generally lacked stable profit models, while the current AI leaders have strong cash flow and actual profitability, with the overall valuation multiples of the technology sector far from reaching the extreme levels of that time. However, the key variable is whether the over $700 billion in AI capital spending by tech giants can truly sustained profit growth. If the productivity gains driven by AI materialize significantly after 2028 as optimists expect, the current valuations will have support; but if the pace of profit realization lags behind the pace of capital investmentthis is the core argument of shorts like Michael Burrythe downward pressure on the market cannot be underestimated. As Goldman Sachs Snider put it, valuation and concentration are measures of "potential energy" that need catalysts to transform into actual declines. And this catalystwhether it be oil price shocks, policy surprises, or AI profits falling short of expectationsis becoming more worthy of attention against the backdrop of multiple signals stacking up.