Walmart plans to open four new fulfillment centers that rely heavily on automation by 2024, the company announced today.

Why it matters: Where Amazon has excelled, Walmart is investing heavily to catch up as its own e-commerce business has grown.

Details: Walmart's upcoming fulfillment centers (where online orders are packed and shipped) will be the first of their kind for the company — given their combination of robotics, machine learning and people.

What they're saying: "[T]hese four next generation [fulfillment centers] alone could provide 75% of the U.S. population with next- or two-day shipping on millions of items," David Guggina, senior vice president of innovation and automation at Walmart U.S., wrote in a blog post.

In contrast: Amazon had 253 fulfillment centers, 110 sortation centers, and 467 delivery stations in North America, not to mention hundreds of thousands of drivers and over 100 Amazon Air cargo aircraft, as of the end of 2021.

The big picture: Both Amazon and Walmart have been spending to bulk up where the other has had the upper hand.

Be smart: Online shopping experiences have become almost indistinguishable from one site to the next, so retailers have been battling one another for customer loyalty through free and fast shipping and returns.

What to watch: The new fulfillment centers will be located in Joliet, Illinois; McCordsville, Indiana; Lancaster, Texas; and Greencastle, Pennsylvania — with each planning to hire more than 1,000 new workers.