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People were surprised when Amazon announced its first brick-and-mortar bookstore in November 2015. Then came No. 2, 3 and 4.

Sixteen months later, Amazon just confirmed to Recode that it is now working on store No. 10 — a location at the Bellevue Square shopping center across Lake Washington from Seattle. Plans for this new location were found in building permits flagged by the building contractor site BuildZoom.

“We are excited to be bringing Amazon Books to Bellevue Square in 2017, and we are currently hiring store managers and associates,” an Amazon spokesperson said.

If it wasn’t clear before, it is now: Amazon really likes the traction it has seen in the four stores that have opened so far and is committed to becoming a physical retailer at scale. New locations are opening in places like Chicago, New York City and the suburbs of New Jersey later this year.

That doesn’t mean the stores still aren’t puzzling. Why does Amazon — bookstore killer — want to become a physical book purveyor? One smart take has been that the stores are as much about selling Amazon devices like the Echo and Kindle as they are about selling books.

When I visited the Seattle location last month, these devices were indeed on display in the physical center of the store. Amazon’s Chief Financial Officer Brian Olsavsky also admitted as much on the company’s last earnings call.

“We test, we innovate,” he said. “We think the bookstores, for instance, are a really great way for customers to engage with our devices and see them, touch them, play with them and become fans. So we see a lot of value in that as well.”

Amazon also showcases some electronics accessories from the AmazonBasics brand in the first Seattle store, as well as items like food processors in the cookbook section.

The stores are also an indirect showcase for the Amazon Prime membership program, because Prime members pay considerably less for books than non-members do. Industry insiders speculate that Amazon could also eventually expand its “just walk out technology” from its new Amazon Go convenience store to Amazon Books locations, as well.

Amazon may never get to the 400 locations that a mall operator mentioned last year, but they are continuing to expand at a fast clip.

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