Is the stock market in a bubble? The AI bubble question for index investors

Is the stock market in a bubble, or is only part of it?

A stock market holds thousands of companies, and a bubble can sit in one corner while the rest trades on earnings. The AI bubble question concerns the corner where valuations rose fastest. For an index investor the useful version asks how big that corner is inside the fund, because a small corner limits the damage and a large corner spreads it.

This reframing replaces a yes or no with a measurement. Instead of arguing about the whole market, you read the weight, the valuation, and the funding of the AI corner. The measurement gives you something to compare next quarter, and a comparison tells you more than any single opinion about the market.

How much AI bubble risk sits inside your index fund?

Start with the factsheet of your fund, which lists the largest holdings and their weights. Add the weights of the companies that sell AI chips, cloud capacity, and models. The sum is your AI exposure through the fund. Funds that weight by company size hold more of the biggest names as their prices rise, so the sum can drift upward without any action from you.

Then repeat the exercise for every fund you own. Savers often hold a world fund, a US fund, and a technology fund, and the same companies appear in all three. The page on S&P 500 concentration in AI stocks shows how the main US index is built, which helps you read the overlap between your funds.

Which valuation measures help an investor judge a stock market bubble?

Three measures cover most of the question. The price to earnings ratio shows what you pay for each unit of profit. A version averaged over 10 years smooths out one-off swings in profit. The earnings yield, which is the inverse of the ratio, lets you compare shares with bonds. When shares offer a thin yield next to bonds, you pay more for the same profit stream.

Compare each measure with its own history and not with a rule of thumb. A ratio that is high for utilities can be normal for software. The AI corner deserves its own comparison, set beside its growth in profit. A high ratio with fast profit growth tells a different story from the same ratio with slow growth.

Who pays for the AI build-out behind the stock market bubble question?

The funding source separates a boom from a bubble. When customers repay the spending through revenue, the build-out supports the prices. When new investors and new debt repay it, the prices depend on a supply of fresh money. The EQOS Asia AI study records about $200B a year invested in AI while 95% of projects fail in production (EQOS Asia AI study, April 2026).

Read company reports for 3 items: capital spending, revenue from AI products, and borrowing. If capital spending grows faster than AI revenue for several quarters, the funding gap widens. If revenue catches up, the gap closes. Writing the 3 items in a table each quarter gives you a trend, and trend is what you need.

How does your time horizon change the stock market bubble answer?

Time horizon decides how much of a fall a portfolio can carry. Savings needed in 20 years can ride through a long decline and recover. Savings needed in 2 years follow the market more closely and carry more risk if prices drop at the wrong moment. The same bubble reading therefore leads to different actions for different savers.

Write down the date for each pot of money: the home deposit, the school fees, the retirement account. Match each pot to an exposure it can carry through a 30% fall, using your own comfort level. This exercise uses no forecast, and it gives you an answer that holds whether AI prices rise or fall.

Why do investors stage purchases when the AI bubble question stays open?

Staging means splitting a large investment into equal parts spread over several months. Each part buys at a different price, so the average price smooths out. This habit suits an open question, because it lets you keep investing while the evidence builds. It also reduces the weight of a single date on the final result.

Rebalancing is the partner habit. Once a year, bring each holding back to its target weight. When AI shares grow beyond their target, you sell part of the gain and restore the plan. The rule decides in advance, so your choices do not depend on headlines. A licensed adviser can fit staging and rebalancing to your situation.

What does the EQOS Asia score add to the stock market bubble check?

The EQOS Asia AI study scores the enterprise AI market at φ(S) = 0.337, in the fragile zone where a shock can tip the system (EQOS Asia AI study, April 2026). The score measures structure and adoption, and it sits beside the index numbers as an independent reading. The Λ simulator lets you recompute it for your own case.

For a family office, a company treasury, or an investor with a large AI exposure, a 30-minute pre-diagnostic applies the same scoring to your decision. You bring the fund list and the horizon, and the session returns a score and a ranked set of options. The mother guide adds the concentration data that decides how far a fall would spread.

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About the author

Stéphane Jambu

President, EQOS Forecast Asia

Stéphane Jambu leads EQOS Forecast Asia and works as a consultant in e-commerce, search visibility, and AI. LinkedIn profile