I searched and didn't find this type of question posted since 2011, forgive me if I missed a more recent similar thread, just wanted to see if there is fresher information.

I'll be flying SEA-OAK on Sunday, but the flight does not arrive until almost midnight. However, there are two flights, SEA-SFO that would get me there earlier and have availability as of now. My experience and understanding is it's at the discretion of the gate agent to allow the co-airport standby. Wondering if that is correct and if I'll have better luck calling an agent or going to the service desk at SEA?