Speaking to Business Insider in an interview published on Monday, Steve Luna, a spokesman for shoe reseller Flight Club, said that the Nike HyperAdapt 1.0 sneakers “have sold extremely well.” Luna added the sneakers’ popularity and short supply make them extremely valuable on the resale market and could be worth as much as $4,000.

Nike (NKE) released the HyperAdapt 1.0 earlier this month. The sneakers come with cables and pressure sensors that can adjust its laces to fit the wearer’s feet. They also have LED lights on the soles that tell wearers how much battery life is left. According to Nike, the HyperAdapt’s battery, which powers the lacing feature, can last about two weeks on a single charge.

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The HyperAdapt sneakers aren’t specialty sneakers like Jordans or limited editions, but at $720, have a hefty price tag. Nike is also treating the sneakers like limited editions by offering them in just a handful of locations and requiring customers to make an appointment to try them out. Nike plans to make more units available in the coming weeks.

Since the HyperAdapt 1.0s went on sale earlier this month, some owners have offered them on eBay (EBAY) to make a profit on their purchase. Pricing on the sneakers has varied based on shoe size, but they’ve generally sold for thousands of dollars.

For its part, Nike hasn’t commented on the sneakers’ success and didn’t respond to a Fortune request for comment on HyperAdapt 1.0 sales figures. However, another shoe reseller, Stadium Goods, told Business Insider that it too is seeing strong demand for the sneakers. That said, its founder, John McPheters, said the success has more to do with the “technology and rarity of the sneakers” than their intended use as shoes.

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Regardless, the early demand seems to support Nike CEO Mark Parker’s claim earlier this year in an interview with CNBC that self-lacing sneakers will be ubiquitous one day.