Mwenenzi

Complimentary upgrades on international flights are not the norm. Some ffp's have an upgrade instrument for top tier status holders. Like SWU for AA. But only able to be used on AA marketed and operated flights.

Oneworld alliance (AA, AS, BA, CX, JL, AY, QF etc) does not have a cross airline upgrade system. AA-IB-BA have a (out of alliance) cross airline upgrade system, but has onerous t&c's (including high cost base fare) so little use for most passengers. AA-AS have a (out of alliance) cross airline upgrade system with t&c's but many pax looking for upgrades.

Star alliance (UA, LH SQ etc) does gave a cross airline upgrade system. But has onerous t&c's (including high cost base fare) so little use for most passengers.

So for international flights always expect to fly in the seat you buy. Even getting a cash & ff miles upgrade on the airline of your ffp will be hard, and far from guaranteed. Upgrade policy between USA and non USA airlines is very different. Paid long haul business class is where airlines get a lot of money. Nothing in it for them to give away upgrades or sell upgrades at very low cost