No one can reliably say how long the AI-led bull market will last. High U.S. equity valuations raise the stakes if expectations disappoint, but they are not a countdown to a downturn. Bonds look more useful as portfolio ballast than they did when yields were unusually low: higher starting yields offer more income and may help absorb some price pressure. They are a potential cushion, not protection against losses.
Can anyone tell how long the AI bull market will last?
No. A high valuation can mean investors are paying a lot for expected future earnings, but it does not reveal when prices will turn or whether they will fall. The AI theme may continue to support earnings and investor enthusiasm; it may also disappoint if growth, profits or adoption fall short of expectations. Neither possibility supplies a reliable market-timing signal.
Vanguard’s valuation analysis, dated July 22, 2026, and using data through June 30, put broad U.S. equity valuations at effectively the highest percentile in its historical sample, after previously measuring them at the 99.7th percentile. That is a statement about the valuation level relative to that sample, not a forecast of when a bull market will end. The measure covers broad U.S. equities, rather than providing a clock for AI-linked stocks in particular.
Why do bonds look more useful now?
The key change is the income available at the time an investor buys. A higher starting yield gives a bond portfolio more income to offset some price declines if yields rise further. Vanguard’s fixed-income discussion describes that income as a cushion against future yield increases; its 2026 outlook for bond returns also frames bonds as useful even without rate cuts.
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That cushion is not principal protection. When market yields rise, prices of existing bonds generally fall, and the effect is usually greater for bonds with longer duration. Income can offset some of that decline over time, but it does not ensure a positive return over a particular period. Inflation can also erode the purchasing power of both principal and interest.
Starting yield matters, but it is not the whole return
A bond’s yield is a useful starting point for thinking about its income potential, not a promise of what an investor will earn. The result also depends on changes in market yields, credit losses, inflation, fees and, for taxable investors, taxes. Vanguard’s 2026 outlook, published in late 2025, projected returns of around 4% annually for high-quality U.S. bonds over the coming decade. That is a model projection—not a realized result, guaranteed return or short-term forecast. Vanguard’s methodology presents nominal returns, excluding inflation, taxes and investment expenses, and cautions against using long-term forecasts as short-term expectations.
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What is pushing yields, and what does the Fed have to do with it?
Bond yields reflect more than Federal Reserve rate decisions. Vanguard has pointed to persistent inflation, concerns about fiscal sustainability and borrowing demand connected to AI infrastructure investment as contributors to higher global yields. These are several pressures, not proof that AI spending alone is driving rates.
The Federal Reserve’s Monetary Policy Report, submitted July 10, 2026, described the largest Treasury yield increases at shorter maturities. It attributed that pattern to market expectations for the federal funds rate pushing up real rates. This helps explain why a bond’s maturity and interest-rate sensitivity matter: a change in expected policy rates does not necessarily move every part of the yield curve by the same amount.
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Vanguard has described a 10-year Treasury yield settling meaningfully above 5% as a risk scenario. That is not a reported current yield or a prediction. It illustrates the kind of further yield increase that could put pressure on existing bond prices.
Which bonds could provide a cushion?
“Bonds” covers investments with different risks. High-quality government bonds are not interchangeable with lower-quality corporate or high-yield credit, and a fund holding one category can behave differently from a fund holding another. Consider these distinctions before comparing an investment with a stock allocation:
- Duration and rate sensitivity: Longer-duration bonds generally react more to interest-rate changes. A shorter-duration holding may have less sensitivity to rising rates, but its income and reinvestment prospects can differ.
- Credit quality: Government and other high-quality bonds have different default risks from lower-quality corporate debt. In a growth shock, credit-heavy holdings may not provide the same diversification as high-quality government bonds.
- Inflation exposure: Fixed payments can lose purchasing power if inflation remains high. A nominal yield does not by itself show an after-inflation return.
- Taxes and expenses: Taxes depend on the security, account and investor’s circumstances. Fund expenses reduce returns; compare costs alongside yield rather than treating headline yield as take-home income.
Individual bonds and bond funds are not the same
An investor holding an individual Treasury security to maturity can receive its stated principal at maturity, assuming the U.S. government meets its obligations; selling sooner exposes the investor to the market price at that time. A bond fund has no single maturity date for an investor to wait for, and its share price fluctuates as the underlying holdings and market yields change. Government backing of Treasury or agency securities does not prevent a fund’s share price from falling.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to think about a bond allocation without trying to call the market
The evidence supports considering high-quality fixed income as a diversifier, not choosing a universal allocation or a particular fund. A practical review can start with the job the bond holding needs to do in the portfolio:
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Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →- Define the purpose. Decide whether the holding is meant to provide income, reduce portfolio volatility, fund a near-term expense or balance exposure to stocks. Those goals can point to different maturities and types of bonds.
- Match maturity and duration to the time horizon. Money needed soon is exposed to a different set of risks from money invested for a decade. Check duration, not just a bond fund’s name or stated maturity range.
- Check credit exposure. Identify how much the holding depends on corporate borrowers’ ability to repay. A high yield may reflect additional credit risk rather than a better version of a government-bond cushion.
- Account for inflation, taxes and fees. Compare what remains after these factors, especially if the goal is future purchasing power rather than nominal income.
- Choose a mix for a range of outcomes. A portfolio should not rely on the assumption that rates will fall, inflation will fade or the AI rally will reverse on a particular schedule.
Higher yields improve the starting point for high-quality bonds compared with the low-yield period, but they do not establish that every bond category is attractive or that a particular allocation is right for every investor. The useful question is not whether bonds can prevent a stock-market loss; it is whether the specific bond exposure fits the portfolio’s time horizon, income needs and tolerance for rate, inflation and credit risk.
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