The rumor was spun up on Twitter by HXL, which cites unnamed AMD source, and dates mentioned in the tweet are actually coming from an Asus marketing person post over at Chinese Weibo. The dates line up with AMD's B550 motherboard launch and availability, and it is possible that these two refresh Matisse SKUs could launch on the same date.
3750X/3850X.....— HXL (@9550pro) May 22, 2020
Not APU https://t.co/GOz2JOHobW
As Videocardz.com points out, Matisse refresh has also been spotted in Gigabyte's B550 presentation, alongside upcoming Vermeer CPUs and Renoir APUs.
AMD Ryzen 7 3800X and the 3700X were big sellers for AMD, launching at $399 and $329 back in July last year. Currently, the Ryzen 7 3800X can be found for as low as $392 and the Ryzen 7 3700X is down to $289.
Both CPUs are 8-core/16-thread SKUs, and both ship with Wraith Prism stock cooler. The Ryzen 7 3800X works at 3.9GHz base and 4.5GHz Boost clocks and has a 105W TDP, while the Ryzen 7 3700X works at 3.6GHz base and 4.4GHz Boost clock and has a 65W TDP.
The Matisse refresh SKUs could up these clocks a bit and keep the things rolling for AMD until it launches its Ryzen 4000 desktop Vermeer CPUs in September.