ABC counted, on LSEG figures from 16 April to 15 October, how lopsided the US market has become. Technology is about 44% of the S&P 500. Without six big names the index would have risen 4.35% in the window, not 10%. Those six made 57% of the gain. That is not a verdict on artificial intelligence. It is a measure of concentration.

Nvidia is worth, in the Australian reading, about A$7.5 trillion, more than US$5 trillion. Tradmap, on 18 October, put the same firm at US$5.15 trillion and 7.3% of the index, with the top 10 near 40%. In the dot-com peak the top ten held about 27%. The comparison does not mean a crash is due. It means a "broad" index is, in practice, a handful of stocks.

Since April, 230 of the 500 companies have fallen. Their loss, about A$2.9 trillion, was offset by Meta, Microsoft and Apple. Anyone who buys an S&P ETF thinks they hold America. They hold, in large part, a few chip and model labs. RMIT's Angel Zhong said that concentrates risk instead of spreading it. Forager's David Johnson pointed at the Nvidia-OpenAI-Oracle circle: invoices that feed one another.

The Wall Street Journal noted on 5 October that the Magnificent Seven together reached almost US$25 trillion, more than the GDP of any country except the United States, and that Nvidia closed at a record US$5.76 trillion. The figures move week to week. The direction does not: weight is gathering at the top.

For a pension or a fund, concentration is not a theory. If those few names stop, the index stops with them, even if the rest of the economy walks. If they keep rising, the rest of the market can fall quietly, covered by the same six. ABC is not calling a sale or a buy. It is showing an uneven map.

This is not investment advice. Market shares, capitalisations and contribution percentages are snapshots on different windows. Anyone choosing a portfolio needs their own adviser, not a newspaper article.

Image: DXR, New York Stock Exchange, CC BY-SA 3.0, Wikimedia Commons; archive facade, not an October 2026 session.

Sources consulted: A handful of AI companies are distorting the US economy - ABC News; Tech Stars' Market Cap Approaches $25 Trillion - Wall Street Journal.