You might assume you aren’t making big, concentrated bets if you haven’t picked individual stocks. In reality, you don’t need to pick an AI stock or a tech fund, or even choose your own super option, to end up heavily exposed to a single theme. Through diversified funds and default super investment options, that exposure can be built in even without you selecting it.

Right now, the clearest example of this is artificial intelligence. AI has become one of the biggest forces shaping markets, and there is little agreement on what comes next. Some prominent investors, such as Ray Dalio, warn of a bubble, while AI leaders and governments balance safety concerns against the fear of losing ground in the global race.

For long-term investors, the key question is not “Is AI a bubble?” but “How much of your own portfolio depends on the answer?”

As a young investor with a long-time horizon, I’m less worried about short‑term volatility than many others. Sharp swings don’t scare me in the same way they might with someone closer to retirement.

Still, there’s a more important question than whether markets are about to fall: do I know why my portfolio moves the way it does? An informed investor is far less likely to make costly mistakes by overreacting to market movements.

Diversification and understanding what you own

Diversification is often called the only free lunch in investing. I remember hearing that phrase during my first finance class at university. The idea is that spreading your money across enough different assets reduces risk without giving up expected returns. It was one of the first concepts of investing that clicked for me.

What I’ve since realised is that diversification is more fragile than it sounds. You can own hundreds or even thousands of investments and still be exposed to the same underlying risk. Owning more assets doesn’t automatically mean less risk.

Right now, that underlying theme driving many people’s investment outcomes is AI. Semiconductors alone now make up a fifth of the US large-cap market. And that concentration drives returns. In the first half of 2026, nine of the ten stocks that contributed most to the US market’s gains were directly tied to the AI buildout.

Where Australians get their exposure:

That got me wondering how an average Australian investor, who might never buy a single stock directly but almost certainly has exposure through super and managed funds, is exposed to the AI theme. More and more investors are using passive funds: our research shows more than 90% of the A$38.2 billion that flowed into Australian ETFS in 2025 went to passive strategies.

There is an irony as to where that money goes. Our share market is dominated by banks and miners (BHP and big four banks make up about a third of Vanguard Australian Shares (ASX: VAS), the ASX’s largest ETF), so many of us go overseas to diversify. But in Vanguard MSCI International ETF (ASX: VGS), the second largest ETF and a popular way to do that, the ten largest of its roughly 1,300 companies, led by Nvidia, Apple and Microsoft, make up about 27% of the fund. Diversifying away from one concentration can land you in another.

Super is no different. As Morningstar’s Tom Lauricella points out, fund managers tend to stay close to their benchmarks because that’s what their performance is judged against. Super funds face the same pressure through the government’s annual performance test, which measures them against broad market indexes. When a handful of AI-linked companies dominate the index, your super holds them too.

So, even if you have never picked an AI stock or tech fund, your ETF or default super option is already making sizeable bets on one story: AI.

Exposure isn’t always obvious

Many investors think about AI exposure through companies like Nvidia or Microsoft. The reality runs much deeper. Behind every chatbot and AI application sits an enormous amount of physical infrastructure: TSMC manufactures the chips, Samsung and SK Hynix produce the memory, ASML and Applied Materials build the machines and equipment used to make them.

None of these companies sell AI products directly, even though they all benefit from the same investment cycle. The biggest tech companies are expected to spend around US$729 billion on AI infrastructure and other capital investment in 2026, up from US$166 billion in 2023 That money flows into equipment makers like ASML and memory suppliers like Samsung, SK Hynix and Micron, which say capacity shortages could last until 2028. And while none of this shows up as “AI” on your super statement, it’s all there in the default.

It’s showing up in bonds too

Bonds and equities have traditionally moved somewhat independently of each other. It’s a big part of why the classic mix of stocks and bonds is supposed to make your portfolio less risky. But today, many of the same companies that are pushing share prices higher are also the biggest borrowers in the bond market

The biggest tech companies now make up 4.8% of the US corporate bond market, up from 2.7% in mid-2025, according to Capital Group and Bloomberg data.

Hyperscales share of U.S corporate bond market (%)

Australia saw this in August 2026, when Alphabet raised A$5.5 billion in its first Australian dollar bond sale, the largest corporate bond deal ever issued in the country. The transaction was explicitly tied to funding its AI expansion. And because many super funds manage their bond portfolios against broad global benchmarks like the Bloomberg Global Aggregate Index, that debt ends up in the defensive part of your super as well. The result is that one theme, AI, now sits on both sides of a portfolio that was originally supposed to keep share risk and bond risk separate.

How to navigate a market dominated by a single theme

Achieving diversification in this market environment requires more effort. The AI boom shows how one theme can run through equities, infrastructure and bonds all at once. Understanding how tied your portfolio is to that story helps explain why your balance moves the way it does, and makes it easier to avoid poor decisions when markets get volatile

Most of this exposure isn’t intentional; it’s usually the default. That’s why, the next time an AI‑driven wobble moves your balance, you’ll at least know what’s behind it. And that alone is often enough to stop a bad decision. Understanding what’s happening makes it easier to respond rationally rather than emotionally. For long‑term investors, that’s probably more useful than trying to guess where AI goes next.

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