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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsThe S&P 500 reaches the four-year anniversary of its October 12, 2022 closing low on October 12, 2026. Reuters reported that the index had risen 117% from that low as of October 9. The rally has been supported by corporate earnings, a solid economic backdrop and heavy investment in AI infrastructure—but its gains are concentrated, and investors still have to see whether that spending produces lasting profits. Four years of gains alone do not say when the advance will end.
What marks the four-year anniversary?
October 12, 2026 is four years after the S&P 500’s closing low for this cycle. Reuters reported a cumulative gain of 117% from that low in its October 9, 2026 market report. That is a dated measurement, not a live return; index levels move from day to day.
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Whether to call the entire period a “bull market” depends on the definition. A common convention is a rise of at least 20% after a decline of at least 20%, Reuters noted, but market experts do not use one universally agreed rule. The anniversary is therefore a useful marker for examining the advance, not proof that a market phase must end—or continue—on a schedule.
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What has driven the advance?
AI investment and earnings expectations
Reuters identified AI-related capital spending, corporate profits and a solid economic backdrop as important supports for the rally. It reported that S&P 500 earnings were expected to grow more than 35% in 2026, with hyperscalers’ data-center investment cited as a driver. That is an estimate, not a final earnings result for the year.
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Spending on data centers also feeds demand for chips and related equipment. In a September 29, 2026 speech, Federal Reserve Governor Michael Barr said AI investment was boosting business fixed investment and demand for those products. He cautioned that the productivity payoff is uncertain in timing: businesses may need to reorganize their work around new technology before its effects show up in output and profits. As Barr put it, “A key question for monetary policy, both in the near term and for years to come, will be the effect of AI on the productive capacity of the economy and the structure of the labor market.”
Gains have not been evenly spread across sectors
Reuters reported that information technology and communication services were the only S&P 500 sectors to outperform the index over the bull-market period it examined. The Federal Reserve Board’s July 2026 Monetary Policy Report separately said the S&P 500 was up about 9% since the beginning of 2026 and the information technology industry group about 16% over the report’s measurement period. Those are period-specific figures, not current year-to-date readings.
The same Federal Reserve report described sizable market fluctuations in response to AI developments and geopolitical events. It also reported that PCE inflation was 4.1% over the 12 months through May 2026, while core PCE inflation was 3.4% over that period. These inflation readings help describe the economic backdrop in the report; they should not be treated as readings beyond their stated endpoint.
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How concentrated is the rally?
Top-ten index weight
A capitalization-weighted index gives larger companies more influence over its return. Reuters cited J.P. Morgan Asset Management’s estimate that the ten largest S&P 500 constituents accounted for about 40% of the index in the October 2026 report, compared with about 28% in October 2022. This top-ten weight is one way to describe concentration; it does not mean all ten companies have the same business or AI exposure.
Concentration cuts both ways: a small number of large companies can lift the index substantially when their shares rise, but weakness in those companies can also weigh heavily on it. Edward Jones strategist Angelo Kourkafas told Reuters, “The risk of concentration is that if the prevailing theme goes out of favor, portfolios might feel it in an outsized way.”
A separate measure of concentration
The European Central Bank’s June 2026 analysis used an adjusted Herfindahl-Hirschman Index, a statistical measure of how activity is distributed across constituents. Under that measure and dataset, overall S&P 500 concentration was above its historical 95th percentile, and IT-sector concentration was above its 75th percentile. These percentiles are not another expression of the top ten’s index weight: the ECB used a different measure, so the figures should not be directly compared.
The ECB also found equity risk pricing subdued and warned that underperformance among a few large AI-exposed firms could spread to the wider market. That is a risk assessment, not a prediction that those firms will underperform.
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AI spending may not earn an adequate return
Investment can support near-term sales for infrastructure suppliers, but it does not guarantee that the companies making large outlays will ultimately earn profits commensurate with the cost. Reuters quoted Ameriprise strategist Anthony Saglimbene saying, “The AI theme is the defining feature of this bull market.” He also said technology companies face more pressure to prove that current spending will translate into profits. The central uncertainty is not whether companies are spending, but how much lasting revenue and productivity they can capture from that spending, and how quickly.
Federal Reserve Vice Chair Philip Jefferson highlighted one difference between today’s AI-linked firms and many companies associated with the dot-com boom of the late 1990s: “In contrast, the firms most closely identified with AI technologies in today’s market generally have well-established and growing earnings streams.” But established earnings do not settle whether current share prices are justified. Jefferson also noted that price gains have been rapid and that expectations and technology effects remain difficult to assess.
Vanguard’s 2026 outlook sets out both sides of the case. Faster AI diffusion and capital investment could support growth and earnings; expensive investment, competition and weak value capture could instead leave companies with disappointing returns. Its valuation and return projections are forecasts from its research period, not realized outcomes or personalized investment advice.
Higher yields and interest-rate policy
Reuters reported a 10-year U.S. Treasury yield around 5.2% on October 9, 2026, following a recent 24-year high. That is a dated market snapshot. Higher yields can make bonds more competitive with equities and put pressure on stock valuations, while monetary policy affects financing costs and expectations for economic activity. Neither relationship supplies a mechanical trigger or a date for the end of a bull market.
Reuters quoted Nationwide strategist Mark Hackett saying, “Four years is not, by any stretch of the imagination, scary with regards to a bull market,” and, “They don’t end of old age; they end from disease.” His phrasing is a personal characterization, not a market law or consensus forecast. In practical terms, the age of the rally is less informative than changes in earnings, valuations, rates, economic conditions and investor expectations.
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A drawdown could reach beyond portfolios
Federal Reserve Bank of Atlanta researchers modeled hypothetical S&P 500 declines of 25%, 35% and 50% and estimated that lower stock wealth would reduce U.S. real consumption through the equity wealth effect. These are scenario inputs and modeled effects, not forecasts that a decline of any particular size will occur. The analysis illustrates one route by which market losses could affect the broader economy: households that feel less wealthy may reduce spending.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What should readers take from the anniversary?
The rally has had real supports—earnings, investment and economic activity—but its unusually large companies and the AI investment theme have carried substantial weight. The outlook therefore depends not simply on whether AI remains prominent, but on whether spending turns into durable productivity gains and profits, how those gains are distributed, and how valuations respond to interest rates and new information. The anniversary is a moment to assess those exposures, not a clock that predicts the next market turn.
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