T-Mobile executives said Verizon’s network speeds have slowed since Verizon launched an unlimited data plan earlier this year.

Verizon finally launched an unlimited data plan in mid-February, joining its rivals and reversing course after years of decrying the wisdom of offering all-you-can-eat on a high-speed wireless network. The company said last week that it had been on pace to lose nearly 400,000 customers during the quarter, but the new plan helped the company stanch the bleeding.

But the increased traffic sparked by unlimited data has slowed Verizon’s network speeds in recent weeks, T-Mobile CEO John Legere said.

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“An interesting thing has happened since Verizon announced unlimited, and it won’t show up until you get to the next quarter’s results,” Legere said during T-Mobile’s earnings call Monday afternoon. “Verizon’s network has slowed down 14%, and they are now slower on the 4G LTE side than AT&T. And in the same time, the speeds on our network have grown 10%. So when we say there’s only one network built for unlimited, it’s clearly ours.”

A T-Mobile spokesperson said that data was determined by using Ookla’s Speedtest app. T-Mobile initially announced its findings in a press release late last week, saying it compared network speeds of the two operators from January 1 to February 12 to results from the week of April 9 through April 15.

A Verizon representative didn’t respond to a request for comment from FierceWireless. An Ookla spokesperson confirmed that T-Mobile has access to Ookla’s data “and has licensing rights to make claims based on their analysis of that data.”

The quality and footprint of Verizon’s network has long been a key differentiator for the No. 1 U.S. carrier, of course, and it still consistently ranks at the top of results from third-party testing companies. The network-performance gap has narrowed in recent years, though, as Verizon’s smaller rivals have built out their LTE networks and leveraged new technologies and architectures.

Meanwhile, T-Mobile is already rushing to deploy service on the 600 MHz airwaves it bought during the FCC’s incentive auction, which wrapped up last week. It won 45% of the spectrum sold during the event, and it expects at least 10 MHz covering more than 1 million square miles will be clear in 2017.

That new spectrum will help T-Mobile deliver wireless data more quickly as demand continues to soar, Legere said.

“We still have stable ARPU, we see good monetization opportunities, and we do see that our competitors don’t have the ability to do this,” Legere claimed.