John F. Kennedy famously said, “The time to repair the roof is when the sun is shining.” As the S&P 500 rallied from pandemic lows to record highs, diversification has naturally received less attention. Concentrated, domestic, large-cap positions and portfolios heavy on equities have ridden the wave, while traditional diversification—across asset classes, geographies, sectors, and market capitalization ranges—has lagged, without much of an opportunity to earn its keep in a downturn. Yet quietly in the background, a new risk has emerged that could spell trouble if a rainy day comes.

Portfolio diversification rests on a simple premise: Some assets play offense, others play defense, and their returns don’t move in lockstep. That premise is being quietly tested by a single theme that has worked its way into nearly every sleeve of a modern portfolio: artificial intelligence (AI) capital spending. Today, you can hold a “diversified” portfolio of stocks, bonds, and alternatives and still be making a single bet.

AI-linked companies now represent roughly half of S&P 500 market capitalization. And the concentration doesn’t stop at the technology sector. The communication services sector carries substantial AI exposure through Meta and Alphabet, and consumer discretionary through Amazon and Tesla. Even utilities, industrials, and financials are increasingly tied to the AI build-out through power demand, data-center construction, and financing. At the end of the day, owning “the market” (that is, the S&P 500) may not provide the risk mitigation diversified investors intend.

Fixed income may not provide a safe haven, either. AI-related debt issuance is projected at approximately $500 billion in 2026 alone, and AI-linked investment-grade paper now represents a significant component of the US credit market. Bond portfolios that historically moved with rates and issuer fundamentals are increasingly moving with technology company performance.

The “alternatives” sleeve is often further exposing clients to the same underlying bet, just wearing a different label. Private credit, data-center infrastructure funds, and portions of venture and growth equity complete the picture.

The result: A client can be “diversified” across asset classes and still be running a concentrated, single-theme portfolio. The labels on the sleeves have stopped functioning as a reliable proxy for actual diversification.

None of this means abandoning AI exposure. The earnings growth behind the theme is real and explosive. It simply means being able to answer, with a straight face, “If the AI story disappoints, what in my portfolio doesn’t move with it?” If your honest answer is “not much,” it’s worth considering a fix before it’s tested, rather than after.

When correlations break down

It’s tempting to reach for a correlation matrix and call it a day, but that’s a bit like judging how good your umbrella is by using it exclusively on sunny days. Those numbers were mostly estimated while the AI theme was a uniformly positive, earnings-accretive story. Correlations have a well-known habit of rising, sometimes sharply, exactly when a shared driver reasserts itself in a downturn. As the old investment adage goes, in a time of crisis, all correlations go to one. We saw this in 2008 when equities, high-yield credit, and even some hedge fund strategies sold off in tandem as the financial crisis unfolded. It happened again in March 2020, when the COVID-19 shock briefly dragged down stocks, bonds, and gold all at once. The diversification benefits that portfolios are built on, carefully modeled using historical correlation data, can quickly break down exactly when they’re needed most.

Diversification strategies that defy AI concentration

When someone says “I diversify my portfolio by owning stocks, bonds, and alts,” the strategy they really intend is “I own things that respond to different economic engines.” In a world of AI concentration, the granular work to put that strategy into practice requires opening the hood on every sleeve (including the ones that feel safely diversified by name) and asking what drives the underlying economics and valuations. A core bond fund stuffed with hyperscaler and data-center paper isn’t doing the diversification a core bond fund is supposed to do. A private credit fund lending against GPUs is not a diversifier from a technology-heavy equity book.

So what strategies can genuinely diversify exposure right now? This is far from an exhaustive list, but it is a useful starting point for the kind of holdings whose fortunes are largely decoupled from the AI story:

  • International equities, where the sector mix skews toward financials, industrials, and consumer names rather than mega-cap tech
  • Equal-weight, value, and small- and mid-cap tilts, which dilute reliance on the handful of names driving the headline index
  • Sovereign and agency debt, municipal bonds, and TIPS—the boring stuff that still just moves with rates and inflation, the way bonds are supposed to act
  • Market-neutral, long-short, and merger arbitrage strategies, which are built to be indifferent to which direction the market or the AI theme is heading
  • Trend-following and managed futures, which can lean against a reversal in the AI trade rather than ride it
  • Real assets like farmland, timber, and non-data-center infrastructure, plus gold and select commodities as these can act as a ballast that doesn’t care about GPU depreciation schedules

To be clear, this isn’t a call that the AI trade is due for a correction, and it’s not an attempt to predict when or whether one arrives. Nobody can call that with any real confidence. The point here is simpler: Given how much of the market’s engine is now fueled by one theme, investors seeking diversification should fully understand where uncorrelated risk mitigation can truly exist, rather than assuming the sleeve labels are doing that work automatically. A little mindfulness now beats an expensive surprise later.

As always, Cerity Partners is here to help you think this through, whether that’s a quick check-in on your portfolio allocations or a deeper conversation about where the risks and opportunities lie.

If you have any questions, reach out to your Cerity Partners advisor or request an introduction today.

Please read important disclosures here.