Checked my RDU–MSP flight in the app last night just to see what seat I had. Out of curiosity, I looked at First Class and noticed a few red seats that I could actually select. No price shown.
Clicked one, hit save… got an email congratulating me on my upgrade and asking for my meal choice. It’s still showing as confirmed today.
I’m fully expecting it to disappear at the gate, but if not… I may have just found a glitch in the Matrix.