Originally Posted by bruinflyer

Is there a way to check for guaranteed upgrade space for GPUs or RPUs? Basically, do those book into a specific fare class, kinda like "I" is theoretically business class upgrades, thus if you see space in I-class then you can buy an economy and upgrade? I'm happy using the United site or using ExpertFlyer, for the record.

I'm asking because I'm trying to buy a route that is showing 100% availability in the front cabin (2cabin flight, literally no seats are booked yet according to the United sites' seats-available-per-cabin info) but is also showing zero GPU and zero RPU guaranteed seats (it only shows "waitlist").

Caveat: I know there are a bunch of threads on upgrades, I know there are a bunch of threads about EF. I have searched both here in the forums and via Google and I can't find this exact question, so if you know where I can find the answer I'll happily accept a link directly to the answer!