Sprint is on its way to oblivion now that the T-Mobile merger has received government approval, but the increasingly troubled carrier is still going through the motions. It's even preparing to launch a new 5G device with OnePlus. However, Sprint has opted to keep virtually all the details to itself.
As you might know, OnePlus launched a 5G version of the OnePlus 7 Pro in select markets. The US was not one of those markets because we don't have much mid-band 5G, and that's what OnePlus supported. Now that Sprint has launched its 5G network in the 2.5GHz band, we do have some mid-band 5G. It's not unthinkable that OnePlus could get a version of the 7 Pro on Sprint in the near future.
Sprint says that it will announce specs, pricing, and launch timing "soon." The mystery phone will get 5G service in areas of Atlanta, Chicago, Dallas-Fort Worth, Houston, and Kansas City. Sprint's 5G coverage is more expansive than other carriers because of the lower frequency. It's unclear if you'll be able to get the 5G OnePlus phone in other markets.