We are officially witnessing the biggest wave of infrastructure investment in modern US history. Total investment in data centers and AI infrastructure is projected to average 3.63% of US GDP per year from 2025 to 2032, the highest proportion among major infrastructure buildouts since the 1800s. The previous largest investment, railroad infrastructure, represented 2.24% of GDP per year in 1870-1890. This was followed by highway investment that averaged 1.13% of GDP in 1956-1973, while telecommunications and fiber infrastructure averaged 1.10% in 1996-2003. By comparison, electrification stood at just 0.50% of GDP in 1905-1925, while canal investment accounted for 0.66% in 1836-1841. This comes as AI and data-center infrastructure investment is projected to total ~$10.3 trillion between 2025 and 2032. The AI buildout is the largest infrastructure investment in modern US history.