That flight is still going to be US-coded. Try to think of it as a codeshare like any other (for example, if you booked a Cathay Pacific flight on AA.com, it would say "Operated by Cathay Pacific", but the flight would have an American flight number assigned. This only gets confusing between LUS and LAA because the flight numbers are now aligned (so unlike with Cathay, where the AA and CX flight numbers would be different, the US and AA numbers are the same, but the upgrade and crediting rules are still not the same. Beware!