I've actually just found on the site that I can upgrade with 30k miles + $600usd. I've only got 2000 miles so might need to try and buy some more. But seeing as this is an option for my booking, I think the s class is upgradeable! Is this the general way to upgrade?
I am a mileage-plus member but not premier status, I've only flown once with united, and I"m constantly flying on different airlines that are company booked so I've got several memberships across airlines like qantas, singapore air, american airlines.
Having upgraded international segments using points on United, I think I am qualified to answer here. In general for United, so long as you are not booked into Basic Economy or are travelling on an award ticket, yes you can upgrade with miles. The number of miles required and whether you end up paying a cash co-pay for the upgrade depends on where you are travelling to and the fare class you are booked into. To give you a specific example, in 2020 I booked a $900 USD return flight: London Heathrow to Sydney (via Los Angeles) which ticketed as a deep discount (but not basic economy) flight into K class (the lowest fare class United has). I was able to then request an upgrade to Polaris business class for 35,000 miles + $650 co-pay (my status at the time was Premier Gold BTW so by no means top tier elite or anything crazy). The upgrades themselves cleared at check-in, which IMHO represents decent value for United Miles. The S fare class is similar to my K class (albeit slightly more pricier)
To your point about holding elite (Premier) status, it won't impact your ability to request an upgrade. Where elite status does play a role is in prioritizing who gets upgraded. For instance, suppose there are only 8 business class seats available when United starts processing upgrades but there are 20 people requesting an upgrade. Well, first they will begin by prioritizing those who bought an expensive fare (i.e. full Y fare or Premium Economy), then for each fare code (i.e. Economy S) they will prioritize by Elite status, so 1Ks will be ahead of those with Premier Gold versus those with no status. There are some other factors outside your control such as whether your organization has a commercial contract with United, that are also taken into account too. Hence, the best way to increase your chances would be to book flights that have a high number of business class availability from the outset (i.e. 20+ seats available at booking), increase the fare you are travelling on (via a
GG BUYUP), and of course earning higher elite status. None of these by the way are a guarantee your upgrade will clear, you are rolling the dice at every point.
What happens if your upgrade doesn't clear? No worries, your points and co-pay are refunded! What if your flight does upgrade? Well, you'll travel in a higher class of service (i.e. Polaris), have access to the United Clubs and Polaris lounges en-route, and for elite members earn valuable PQPs (based on how much $$$ you spent on the co-pay) towards earning elite status. Is it worth upgrading to Premium Plus (United's Premium Economy)? No! Having flown them a number of times you would be better off sitting in an over-wing emergency exit row which boasts 50+ inches of pitch!
By the way, using points to upgrade is just one method United provides you. They also offer upgrade offers right now when you go into Manage My Booking for your flight. Sometimes these offers can be very appealing (i.e. once I had a $900 offer to upgrade my dirt cheap K fare to Polaris for Auckland to San Francisco)
Hope this discussion provides marginal benefit!
-RooFlyer88
