The AI buildout comes to the bond market

Commentary by Lucas Baynes, Vanguard Senior Investment Strategist

On our “Market views” tab: How AI is becoming a value-stock story

The concentration of U.S. equity returns in a handful of AI-linked companies is by now a familiar story, one we examined in a recent article. Meanwhile, a quieter development is transforming a market many investors hold precisely because it is supposed to behave differently: fixed income.

For most of the past decade, the large technology companies leading the AI buildout have funded their investment from operating cash flow. That era is ending. As capital expenditures by the five “hyperscalers”—Alphabet, Amazon, Meta, Microsoft, and Oracle—surge, an increasingly large share is being financed in the bond market, at a scale with few precedents. For fixed income investors, the question is not whether these borrowers are creditworthy; most carry exceptionally strong balance sheets. The question is what a rapid, concentrated change in the composition of the bond market means for the traditional role bonds play in a portfolio.

The change in supply is striking. Between 2020 and 2024, the five hyperscalers combined issued roughly $35 billion of debt each year, on average. In 2025, that figure jumped to $93 billion. Year to date, they have issued approximately $132 billion, including one multitranche offering of roughly $53 billion, among the largest corporate bond sales on record, and a rare “century” bond that matures 100 years from issuance. Estimates of total AI-related debt issuance for full-year 2026—extending beyond the hyperscalers to the wider ecosystem of chipmakers, data-center developers, and utilities—range from roughly $300 billion to $570 billion.

From the issuers’ perspective, the logic is straightforward. Locking in long-dated funding spreads the cost of a multiyear infrastructure program across the horizon over which it is expected to pay off, preserves cash and flexibility, and takes advantage of high credit ratings that make debt inexpensive relative to equity. Railroads, electrification, and telecommunications, each of which changed how we lived and worked, were all substantially financed by debt. In that sense, the AI buildout arriving in the bond market is not a warning sign, but an indicator that the investment cycle is maturing.

For bond investors, the more important question is whether the current financing wave is temporary or structural. On that front, consensus expectations offer little evidence of an imminent slowdown. Aggregate capital expenditures by the hyperscalers are projected to approach $800 billion this year and exceed $1 trillion annually from 2027 through 2030. In other words, while the pace of growth may eventually moderate, spending levels themselves are expected to remain extraordinarily high. If these forecasts prove broadly correct, the recent surge in bond issuance may be less a one-off financing event and more the beginning of a multiyear shift in corporate bond supply.

For investors in broad bond index funds, this wave of supply is changing the character of the market in three ways:

First, weight. Technology has historically accounted for a modest slice of the investment-grade corporate market, but the sector’s share of the Bloomberg U.S. Corporate Bond Index is now rising quickly as AI-related borrowing accounts for a large share of net new supply. Concentration, long an equity-market phenomenon, is migrating into the asset class many investors hold as a diversifier.

Second, duration. Hyperscaler issuance during the recent borrowing wave has been heavily long-dated, including substantial issuance at 30 years and beyond, increasing the duration exposure entering the investment-grade corporate bond market. Long bonds from a handful of issuers extend the duration of the index itself, subtly increasing the interest rate sensitivity of portfolios that track it.

Finally—largely outside the index—a substantial share of data-center financing is being arranged through private credit and off-balance-sheet structures. Whatever the merits deal by deal, this migration means public balance sheets and public bond indexes no longer capture the full financing picture of the buildout, and the ultimate distribution of risk is harder to observe.

Why does composition matter if credit quality is strong? Because of what investors ask bonds to do.

Investors hold high-quality bonds in large part to diversify equity risk. Yet at the margins, the new bonds being added to the index are increasingly a claim on the same AI investment cycle that has been driving equity returns. Our midyear outlook noted that the AI complex is expected to generate more than half of U.S. earnings growth this year and next; the same complex is now a leading source of net new bond supply. If the economics of the buildout were to disappoint, the channels could correlate. If wider spreads on AI-linked credit arrived alongside weakness in AI-linked equities, it would narrow, at least modestly, the diversification that investors expect from their bond allocation.

Two balancing points are essential. The issuers in question are, for now, exceptionally strong credits, with leverage and interest coverage that most industrial borrowers would envy; nothing here is a solvency warning. And the primary source of bonds’ diversification power—high-quality duration, above all in Treasuries—is unaffected by corporate index composition. The observation is narrower: Within the credit sleeve of a portfolio, sector concentration is rising, spreads are near historically tight levels, and the compensation for that concentration is thin.

We recommend monitoring a short list of markers: new-issue concessions and order-book coverage on large AI-related deals; the spread behavior of hyperscaler curves relative to the broader technology sector; the pace at which financing migrates into private structures; and, ultimately, the capital-spending guidance that determines how much more supply is coming.

For investors, the implications are characteristically unglamorous. Know what you own: A broad “core” bond fund is gradually becoming a larger claim on the AI buildout, and an investor with substantial AI exposure in equities may be adding to that exposure, unknowingly, in fixed income. Rather than relying on credit alone for ballast, investors may be well served by diversifying across the full fixed income opportunity set—Treasuries, securitized assets, and hedged non-U.S. bonds—and letting high-quality duration carry the defensive role in the portfolio.

The bond market is doing what it has always done for transformative technologies: financing them. Similarly, investors should do what they have always done: hold bonds for their role, size credit for its risk, and be realistic about how much any single theme, however promising, should determine the behavior of what are meant to be a multiasset portfolio’s safest assets.