Another donor has stepped forward for free upgrades on United. Bonnie is donating 3 GPUs and 4 RPUs. I haven’t had any takers yet for the GPUs offered by Bill, but I get the fare restrictions severely limiting those who would be eligible. However, you don’t have the same fare restriction on domestic RPUs. Here are the rules again for both:
RPUs: These upgrades are good for any fare as long as the flight stays within Central or North America. There is an exception for some flights outside of this, such as Guam to Manila, but these are rare exceptions that I am not going to detail.
GPUs: These are for international travel, but have significant restriction on what fare class you can apply them to. From the UA page: Global Premier Upgrades are not available on flights booked in fare classes Z, P, S, T, K, L, G or N. Meaning that you can’t use them on the cheapest fares. Even cheap First or Business Class.
The United Upgrade page has the details. Your flight does need to be no later than 31 January.