It’s bigger than the railroad expansion of the 1850s, the Apollo space program that put astronauts on the moon in the 1960s and the decadeslong build-out of the U.S. interstate highway system that ended in the 1970s.

We’re talking about the data centers now being built and financed by some of the world’s biggest companies in the artificial-intelligence boom.

Four U.S. tech giants— Microsoft, Meta Platforms, Inc., Amazon.com and Alphabet’s Google—are planning to spend up to $670 billion to build out AI infrastructure this year alone as they scramble to increase the computing power needed to operate and scale their AI-related endeavors.

It has become an increasingly expensive project, one that the companies finance with their billions of dollars in advertising, cloud and subscription revenue. And if you compare this spending to some of the biggest capital efforts in U.S. history by percentage of gross domestic product, you can see exactly how staggering the figures are.

In fact, it’s dwarfed only by the Louisiana Purchase, completed in 1803, which doubled the size of the U.S.

The companies’ capital spending has been increasing as a percentage of their annual revenue the past few years. In 2026, Meta’s spending could amount to more than 50% of its sales for the first time ever, according to analyst projections.

Investors and analysts initially expressed concern about Meta’s spending plans for 2026 but gave the company a reprieve after it posted record quarterly earnings attributed to AI-driven improvements, and forecast even bigger potential growth in the current quarter.

Amazon’s investors, however, didn’t take kindly to its plans to ramp capital spending up by nearly 60% to $200 billion this year: On Friday, the company lost $124 billion in market value.