It was a nice surprise.
Years ago I opened a BA credit card because Chase had a good SUB, and I'd planned a trip to Europe. That never happened, and I've been slowly cashing out Avios ever since.
My final trip was this past weekend - I used those Avios to book Alaska to SAN. When I booked, I did not have enough to buy first class ... I know it's lame on an E175, but I like my shoulder room even on short flights.
Between the booking and the flight, I made Atmos Silver... I've never in my life flown often enough to earn status, but this year the stars aligned and I got there. This flight to SAN was the first one I'd taken after having reached Silver.
Much to my surprise, both inbound and outbound flights were automatically upgraded to 1st. Economy tickets purchased with points on a partner turning into 1st class is pretty rad. Icing on the cake of my trip!