Amazon opened its first checkout-free store in early 2018, and it has said it could open as many as 3,000 cashierless Amazon Go stores by 2021. So far, most have been smaller convenience stores, but people have speculated that it's only a matter of time before Amazon brings the cashierless checkout to large supermarkets. That said, it's unclear how exactly Amazon will make that model work with the many items in a grocery store that need to be weighed before purchase, like fresh fruit and vegetables. But last month, Amazon confirmed that its engineers are testing Go tech at a 10,400-square-foot retail space in Seattle.

Amazon is notorious for trying multiple ideas at once, and just last week, the company said it plans to roll out another grocery store format. Supposedly, that model will be different from Whole Foods but will still have cashiers. Amazon is also considering licensing its cashierless tech to other retailers, like movie theaters, stadiums and airports.

Amazon did not immediately respond to a request for comment.