A small group of AI companies are creating a lopsided US economy

Key points

• A small group of AI-linked companies is driving much of the US stock market's gains, prompting warnings about concentration risk. Tech stocks account for about 44 per cent of the S&P 500's total value.
• Six companies, including Nvidia, Micron and AMD, produced most of the index's gains since April. Experts say some AI labs still earn far less than they spend, and that companies are increasingly investing in one another.
• Analysts say the technology may transform the economy, but investor returns are uncertain.