Nvidia’s market capitalisation has lifted its share of the S&P 500 above 8%, a level no single company has reached in the benchmark’s recorded history. Combined with Microsoft, the two companies now represent roughly 15% of the index, underscoring the dominance of a handful of mega-cap technology names. That concentration is rippling through the wider market. The ten largest constituents make up 40% of the S&P 500, while the biggest 10% of U.S. stocks control about 76% of overall U.S. equity value—both all-time highs and well above peaks seen during the dot-com boom and before the Great Depression. Technology’s own index weight is hovering between 34% and 44%, matching records set in March 2000. Rich valuations accompany the narrowing leadership. The Technology-Media-Telecom group trades near 27 times forward earnings, and the S&P 500’s cyclically adjusted Shiller P/E has climbed to 38.8, its loftiest point since 2000. Globally, the IT segment of the MSCI World index also fetches 27 times earnings, while the Nasdaq’s performance relative to the small-cap Russell 2000 has reached a record multiple of more than nine. Investor positioning mirrors the trend. Bank of America’s August survey of 169 fund managers overseeing US$413 billion found that 45% view a “long Magnificent 7” wager as the market’s most crowded trade, a reprise of the sentiment earlier this year. The findings highlight how heavily investors are relying on a narrow slice of the market for returns, raising concerns that any reversal in the sector could reverberate across global portfolios.