https://www.cnet.com/news/thanks-to-samsung-and-verizon-5g-is-about-to-all-get-up-in-your-face-fast-data/

Samsung's exact US launch date is unconfirmed, but the S10 5G is rumored to go on preorder sale April 18, with a May 16 launch. It'll come exclusively to Verizon before heading to AT&T, Sprint and T-Mobile. 

It's possible that Samsung is deliberately holding back the S10 5G launch until Verizon's new 5G network becomes a little more stable, and perhaps more widespread. Right now it's available only in Chicago and Minneapolis (and in mere downtown hotspots at that), but Verizon says its 5G service will come to 30 cities by the end of 2019.