I’ve had 4 B fares (A/O fares that are booked as B for the domestic leg — verified that was the case in all) in the last month as a Plat.
None cleared ahead of time with an instant upgrade but 3/4 ended up clearing at the gate (RDU - EWR, IAD - RDU x2) and one ended up as #1 on the upgrade list (RDU - IAD which is fine since it’s maybe a 35 minute flight)