Really weird. I just ran SFO-AMS on July20-27. It nominally returned a P for the domestic legs and an A for the international legs, which I expected to be a P-UP, booking into A. But here's the fare construction:

City Pairs Fare Class Fare Basis Code
SFO - CHI S SAA21AKN
CHI - AMS A ANC2S
AMS - SFO A ANC2S

So the A's are true A fares, not UP's. That S fare I don't understand at all, it's not even an UP. And why UA isn't selling any discount business fares on this route doesn't make much sense to me at all. The buckets are 9 all the way down to P.

Edited to add: If I restrict the search to J, C, D, Z, and P, I get a construction with Z fares for the international segments that's almost a $1000 higher.

So for whatever reason, the A is just the cheapest front cabin fare UA is selling on this route right now.