It is for some things, but not for other things.

SJU is "domestic" for:
- lounge access (not offered within "North America")
- meal service (basic or basic plus, depending on flight length...but definitely not Flagship standards)
- stickerless e-upgrades are valid (within "North America")
- no passport required; no FIS procedures upon return obviously


SJU is "international" for:
- premium cabin marketed as "Business" instead of First"
- crews are international (overwater qualified)
- equipment must be overwater certified (so no S80s or RJs)
- some fare rules indicate "International"



I'm sure there are others that I'm forgetting....