Originally Posted by
jroff1
Even though codeshare flights are technically not eligible, I believe the general experience has been that US preferred's receive all of their US benefits while traveling on US metal, even when booked as a UA codeshare.
Datapoint: just got my confirmation from US for a UA ticketed/UA codeshare flight number on US metal.
Upgrade Status: Complimentary upgrades not offered
So, it appears they may have closed this loophole.