There is a week, four times a year, when the world’s markets hold their breath — not for a central bank, but for a handful of technology companies reporting earnings. The largest tech firms now constitute such an outsized share of major stock indices that a single results statement, and the guidance whispered after it, can move trillions in market value before breakfast. Monetary policy still matters. But the earnings calendar of five or six companies has become its rival.
How the concentration happened
The mechanics are compounding. Index funds channel a growing share of the world’s savings into the biggest companies by formula; those companies’ profits — from cloud computing, advertising, devices and now AI infrastructure — have grown into economies of their own, with individual firms reporting quarterly revenues rivalling the output of mid-sized nations. Their investment programmes move other markets too: the AI data-centre build-out is now a measurable force in construction, power and chip supply chains. Market structure analyses by the Bank for International Settlements have begun flagging index concentration as a financial-stability question, not merely an investment curiosity.
The AI line item
Every recent earnings season has turned on one interrogation: is the enormous capital spending on AI infrastructure earning its keep? Investors reward evidence of AI revenue and punish vagueness, sometimes within the same week from the same company. The result is a strange new ritual in which the future of a technology is re-litigated quarterly, in public, by its largest builders. Our business pages decode each season’s results — the numbers beneath the headlines and the guidance beneath the numbers.
What it means for ordinary investors
Concentration cuts both ways: index investors have been carried by these firms’ strength, and are exposed, by the same arithmetic, to their stumbles. Diversification advice has quietly updated — spreading across regions, sizes and styles matters again after a decade in which the biggest index simply won. The giants may keep winning. But a market whose fate hangs on six earnings calls is a market that has outsourced its judgement, and the bill for that convenience tends to arrive unannounced.
Regulators watch the same numbers with different questions: about competition, about the intertwining of the largest firms through each other’s clouds and chips, about what happens to the index if one stumbles badly. Concentration is not a scandal. It is a condition — and conditions, in markets, are what risk management is for.
For the companies themselves, the earnings call has become a genre of statecraft: ninety minutes in which a chief executive must narrate the future convincingly enough to defend a valuation built on it. Few performances in business carry more money per minute. The calendar, four times a year, is already circled.
