a16z says AI infrastructure buildout has surpassed the railroad era in share of U.S. GDP

Andreessen Horowitz said in its second annual State of the Market report, released on Sept. 30, that the current AI infrastructure buildout now represents a larger share of U.S. GDP than the 19th-century railroad boom, a comparison often used by markets to frame the scale of the cycle. The firm said capital spending by the four largest U.S. cloud providers and other hyperscalers reached about $416 billion in 2025, could rise to roughly $780 billion in 2026, and may exceed $1 trillion a year starting in 2027. According to the report, technology companies accounted for about 76% of S&P 500 earnings growth in 2026, while high-tech equipment, software and R&D together made up about 55% of total U.S. capital expenditure. a16z also pushed back on the idea that GPUs quickly lose value after three to four years, saying Nvidia’s A100 chips installed one or two years ago still perform well even as demand for the newer B200 remains strong. The report added that AI adoption is broad but still shallow: about 69% of S&P 500 companies have launched AI applications, nearly 30% reported measurable benefits, yet only about 2% consistently track outcomes.