Originally Posted by
mgcho
On my recent returned trip from Asia on 31st May, I was surprised to get free upgrade from coach to First class on Narita -->Salt Lake City on AirBus 330 with Delta Metal.

I saw several other people got upgrades like me and they were equally happy.
Congratulations on the UG, likely an Op-Up as
RSSrsvp suggests.
You were actually upgraded to Business Class not First Class, as DL does not have an international First Class cabin.