Looking to take a trip to eastern Europe at some point from May to July ideally out of IAH and I'm flexible on dates. If I'm going on United this means probably flying through London, Frankfurt or Munich. I would like to use a GPU but based on somewhat substantial fare code search, I'm not seeing and flights on which I could confirm my upgrade instantly, leading me to conclude that that these fares have not been released yet. Any advice on if my suspicion is correct and if so, when these typically open up? Thanks for any assistance.