Click below to display this full wiki and read if you have general questions about using GUCs -- they may be answered here!
NOTE: Both GUC and RUC rules are listed below because the way GUCs work on domestic routes is now different than how RUCs work

New Fare Table for GUC/RUC Effective 2/1/2022

*****GUC*****

Flight has First Class
MC/C+ = Purchased
First = Last Seat J (Old Policy = OY)

Flight has DPS only
MC/C+ = Purchased
DPS = Last Seat (GUC=P / RUC=G) (Old Policy = RY)

Flight has D1 with no DPS
MC/C+ = Purchased
D1 = Z (Old Policy = OY)

Flight has D1 with DPS
MC/C+ = Purchased
DPS = Last Seat (GUC=P / RUC=G) (Old Policy = RY)
D1 = OY @ T-24h15m

Flight has D1 with DPS
DPS = Purchased
D1 = Z (Old Policy = OY)

Note: If GUC applied to domestic flight, it has better inventory than RUC (better chance for D1 transcon or to Hawaii)

*****RUC*****

Flight has First Class
MC/C+ = Purchased
First = Z (Old Policy = OY)

Flight has D1 with no DPS
MC/C+ = Purchased
D1 = OY (no change in old policy = OY)

Delta is using public inventory buckets J Z P G (and non-public bucket OY in some cases) to determine GUC/RUC availability. However once they have confirmed you the system converts the segment in your reservation to a different bucket. Here is the class mapping:

GUC Usage
MC or C+ purchased / Upgrade to DPS / P class needed / Books into RV (Clears at T-24.15 into D1 as OX if OY available)
MC or C+ purchased / Upgrade to D1 (no DPS) / Z class needed / Books into OK
DPS purchased / Upgrade to D1 / Z class needed / Books into OK
MC or C+ purchased / Upgrade to FC (no D1/DPS) / J class needed / Books into OV

RUC Usage
MC or C+ purchased / Upgrade to DPS / G class needed / Books into RX (Clears at T-24.15 into D1 as OX if OY available) ****THIS AIRCRAFT CONFIG MAKES NO SENSE DPS IS NOT SOLD ON RUC ROUTES, MAYBE THIS IS FOR FUTURE PLANS?****
MC or C+ purchased / Upgrade to D1 (no DPS) / OY class needed / Books into OX
DPS purchased / Upgrade to D1 / OY class needed / Books into OX ****THIS AIRCRAFT CONFIG MAKES NO SENSE DPS IS NOT SOLD ON RUC ROUTES, MAYBE THIS IS FOR FUTURE PLANS?****
MC or C+ purchased / Upgrade to FC (no D1/DPS) / Z class needed / Books into OL

New Delta.com Upgrade Availability Indicators that appeared 2/1/22 and what they mean

***The GUC/RUC indicators are still based on married segment logic as of 10/2022. You likely will need to look up desired flights individually to see correct upgrade indicator. Also, indicators currently ONLY work for DL coded/ DL operated flights. You still need to use an external tool like Expert Flyer to find space on AF/KL/VS/KE.

Dom D1 Tag meaning:
Global Upgrade Certificate Available = GUC in Z (OY = 0 for RUC)
Upgrade Certificate Available = GUC in Z /or/ RUC in OY both available

Dom F Tag meaning:
Global Upgrade Certificate Available = GUC in Last Seat J (Z = 0 for RUC)
Upgrade Certificate Available = GUC in last seat J /or/ RUC in Z both available

Example D1 Flights from JFK - LAX (flight numbers are fictitious)

DL 01
Dom D1 flight
Actual Availability: J5 C4 D4 Z3
Hidden Availability: OY2
Website indicator: Upgrade Certificate Available
Actual decode: (2 RUC (OY) open, 3 GUC (Z) open)

DL 02
Dom D1 flight
Actual Availability: J5 C4 D4 Z3
Hidden Availability: OY0
Website indicator: Global Upgrade Certificate Available
Actual decode: (0 RUC (OY) open, 3 GUC (Z) open)

DL 03
Dom D1 flight
Actual Availability: J3 C2 D2 Z0
Hidden Availability: OY0
Website indicator: No flag - neither is available GUC (Z0) and RUC (OY0)

DL 04
Dom First flight
Actual Availability: J3 C2 D2 Z1
Hidden Availability: n/a
Website indicator: Upgrade Certificate Available
Actual decode: (1 RUC (Z) open, 3 GUC (J) open)

DL 05
Dom First flight
Actual Availability: J3 C2 D2 Z0
Hidden Availability: n/a
Website indicator: Global Upgrade Certificate Available
Actual decode: (0 RUC (Z) open, 3 GUC (J) open)

DL 06
Dom First flight
Actual Availability: J0 C0 D0 Z0
Hidden Availability: n/a
Website indicator: No flag - neither is available
Actual decode: (0 RUC (Z) open, 0 GUC (J) open)

Other Upgrade Rules (post 01 Feb 2022)

Using GUCs to upgrade companions:

• "There is no limit to the number of travel companions you can upgrade with an Upgrade Certificate — even if you don’t need to use one for yourself.* In order to upgrade your companions, they must be flying in the same reservation or a linked reservation and each companion will require their own Certificate to be upgraded."
• *but if you are using an AMEX Companion Cert then you must use GUCs for both passengers or none (must travel in same cabin)

Using Delta Global Upgrades

DL page: https://www.delta.com/us/en/skymiles...llion-upgrades
scroll down to "Upgrade Certificates" and start reading there. Other primary sections of interest may be "Where to Use Upgrade Certificates" and "How the Upgrade Certificates Waitlist Works", or scroll to the bottom to expand the full T&C (also the pre-2022 historical terms are still available as well)

Choosing upgrades as a choice benefit

• Starting with the 2022 Medallion year, upgrade certificates now expire at the end of the Medallion year they are associated with, i.e. for MQ*s accumulated in 2022, to qualify for 2023 status, any certificates selected with 2023 Choice Benefits expire Jan 31, 2024 regardless of when you select them. (Historically, certs expired a year after the date on which you selected them but this is no longer the case). So if you are confident you will be using GUCs (or RUCs for that matter) there is no longer much reason to wait to select them -- the only real reason to wait is that if you reach the end of the year without having needed to select certificates, you would still be able to choose something else like SkyMiles as a Choice Benefit.
• Certificates usually appear in your account within 24 hours of selection (and in most cases far sooner than that, within a small number of hours). If you have selected your choice benefits very recently (within the last 24-48 hours), the phone agent may not yet be able to see your upgrade codes, but you can read the codes to the agent from the My Wallet page on Delta.com
• All Diamond Medallions also receive a Platinum Medallion choice benefit, even if just renewing existing Diamond status in a year, so DMs could for example select 4 RUCs as their Platinum choice benefit and 4 GUCs as one of their Diamond choice benefit, or 4 RUCs as their Platinum choice benefit and 8 more RUCs as one of their Diamond choice benefits
• However, it is not possible to select 8 RUCs as one Diamond choice benefit and 4 GUCs as another, nor select 4 GUCs more than once for a single year's Diamond choice benefits -- so the most GUCs anyone can currently earn in a single year is 4
• You do not need to select all three DM benefits at the same time, nor do you need to select your PM benefit before your DM benefits
• Upgrades can be used after you are no longer a Diamond Medallion as long as the upgrades are still valid, though non-DM-line phone agents will be less familiar with them, so they may be harder to use or run a higher risk of being processed incorrectly, so it may be worth booking your GUC flights before your DM status expires if possible.
• All flights to be upgraded must be flown, not just requested, by the expiration date of the upgrade certificates, though there have been some examples of short extensions offered by phone agents (for example, to the end of the month of the expiration date) as long as the upgrade is able to be confirmed before the certificates expire. In this case it is important to push the agent to make sure the ticket is reissued right away, since it will not be possible to reissue the ticket after the GUC expires. You can tell if the ticket has been reissued because the ticket number on the booking will change from what it was when you originally booked in coach, and the GUC will be marked as "closed" in your wallet on Delta.com.

Finding upgrade space

• If you book a main cabin ticket, GUCs may now only be used to clear in advance into Premium Select; you can still use a single GUC to upgrade from main to PS, then waitlist for D1, but in this case you will not clear any earlier than T-24h. Note: in most cases gate agents in other countries may not know how or be willing to clear the day-of-travel upgrade list, in which case you are relying on space to open up before the gate takes control and being able to call in to get a phone agent to process the upgrade for you.
• If you book PS outright, you can clear into D1 any time (including at booking) subject to availability similar to how GUCs used to work pre-2022.
• The website now shows certificate availability since early 2021: https://www.flyertalk.com/forum/delt...d-12-31-a.html however quirks have been reported both with the website showing availability and agents saying no, or the website not showing availability but people clearing at booking. Unclear how much of this is buggy Delta IT and how much of it is uninformed/junior agents.
• Delta phone agents and Twitter/chat reps can also check for available upgrade space
• ExpertFlyer cannot be directly use to look for space in any two-letter inventory bucket, including the O_ upgrade buckets, but in some cases upgrade inventory may map onto a paid fare bucket such as Z; there have been observed quirks here as well so YMMV.
• Upgrade space is not necessarily correlated with award space

Other upgrade rules

• It is possible to request upgrades in one direction of a roundtrip only, for example if you had 4 US-Europe trips planned and only 4 GUCs, you might decide to upgrade the eastbound flights only as they are overnight flights and remain in economy for the westbound flights.
• Unlike AA and UA upgrades, DL upgrades cannot be gifted to someone whom the SkyMiles member is not traveling with. However you can use GUCs to upgrade any number of companions up to the limit of however GUCs you have available, even if you do not need to upgrade yourself (i.e. you already purchased J).
• The priority order of GUCs, RUCs, mileage upgrades, and complimentary upgrades is not 100% clear, but it is known that GUCs and RUCs have higher priority than complimentary upgrades, and that GUCs and RUCs appear to have equal priority. It is listed on Delta.com that GUCs and RUCs clear first by medallion level and then by time of request, which is different from the upgrade priority used for complimentary upgrades (which is also listed on the website)
• Gate agents can only process an upgrade if you are on the upgrade list. If one is not on the upgrade list because the GUC was incorrectly applied by a ticketing agent, that mistake can only be fixed by Delta reservations prior to 3 hours before schedule departure. If you check-in for a flight with a GUC supposedly applied (assuming it has not already cleared), and are not on the upgrade list, then something is wrong. The three hour deadline cannot be over-ridden, and a flyer with a mis-applied GUC will not be upgraded at the gate even if seats are available at departure.

Using upgrades on KLM

Dedicated thread: https://www.flyertalk.com/forum/delt...grade-klm.html

• "For travel on KLM-operated, Delta-marketed flights this certificate may be used to upgrade on published fares booked in Y, B, M, H, Q, K, L, U, T, X or V class and all fare classes upgrade into Z class. For travel on KLM-operated flights marketed by KLM, fares booked in Y, B, M, K, H, L, Q, T, N, R, or V class are eligible to upgrade into Z class. For travel on KLM-operated flights marketed by AF, this certificate may be used to upgrade on published fares booked in Y, B, M, K, H, L, Q, T, N, R, or V class into Z class. "
• NOTE: some of the combinations above are only (relatively) recently eligible for GUCs. Phone agents may not be familiar with the new rules, and may need to be gently pointed in the direction of the DL T&C on their own website.
• NOTE 2: Although as of Sep 2022 the website T&C have not been updated to reflect this yet, KL's rollout of Premium Economy is under way, and on routes where it is available, similar to on DL and AF you can only upgrade one cabin with a GUC.
• In the course of processing the upgrade of a Delta-marketed, KLM-operated flight, Delta reissues the KLM flights on KLM flight numbers when they issue the upgrade
• Make sure they reissue the ticket before you hang up on the call. If the ticket is not reissued, the partner airline will cancel the segment entirely within several days, as from their perspective they will see a reserved seat without a supporting payment (the certificate).
• It is not possible to waitlist for upgrade on KLM flights, nor to go to the airport upgrade list, so space must be available in advance in order for the upgrade to clear. Many agents will offer to put you on the waitlist, but putting you on the upgrade waitlist for a KLM flight will simply never clear so you're better off monitoring it yourself (see next bullets).
• KLM upgrade space can be checked on ExpertFlyer.com (requires a paid membership). ExpertFlyer also allows users to set alerts for particular fare classes becoming available, which could be useful in lieu of being able to waitlist -- you can set an ExpertFlyer alert for "Z" availability and then call Delta to grab the upgrade if you receive an ExpertFlyer alert that it becomes available. If you don't want to pay for an EF subscription you can also search ITA Matrix and force "f bc=z" in the extended codes to search only for Z availability.
• KLM upgrade space on a single segment is different if you search that segment alone vs. if you search a connecting itinerary involving that segment. So if you are looking for KLM upgrades ORD-AMS-JNB, you need to search ORD-JNB in ExpertFlyer to see the true availability; even if there is space on ORD-AMS and AMS-JNB, if it Z space doesn't show up for ORD-JNB you won't be able to upgrade. Unfortunately this means that ExpertFlyer availability alerts, which can only be set on a segment-by-segment basis, are not useful for monitoring KLM upgrade availability on connecting flights.
• In some cases, adding a DL domestic connecting flight can change KLM upgrade availability. For example ATL-AMS on KLM may show availability but MCO-ATL-AMS may not. Example. Unfortunately some more complex routings, such as forcing an extra connection to find KLM upgrade space (flying JFK-ORD-AMS-CPT instead of JFK-AMS-CPT), do not show up on ExpertFlyer so you are at the mercy of hopefully finding Delta agents who know what they're doing.
• Bookings with KLM ticket numbers (starting in 074) can be upgraded using the same rules as bookings with Delta ticket numbers (starting in 006). Delta-operated, KLM-coded flights can be upgraded under the same rules as any other KLM-coded flight. Delta-coded, Delta-operated flights booked on a KLM ticket number can be upgraded the same as if they were booked on a Delta ticket number, so in any fare class other than E.
• There have been numerous challenges with KLM upgrades, so be careful, be persistent, and make sure you request the upgrade within the no-risk cancellation window of the ticket so you can cancel if it doesn't work as expected.
• More KLM upgrade reading: 1, 2, 3, 4, 5, 6

Using upgrades on Air France

Dedicated thread: https://www.flyertalk.com/forum/delt...20-onward.html

"For travel on Air France-operated flights marketed by Air France and booked in Y, B, M, K, H, L, Q, T, N, R, or V class, customers can upgrade into A class (Premium Economy), or they can upgrade from W, S, or A class into Z class (Business Class). For Air France-operated flights marketed by KLM, customers with a published fare booked in Y, B, M, K, H, L, Q, T, N, R, or V class can upgrade into A class (Premium Economy), or they can upgrade from W, S, or A class into Z class (Business Class). For Air France-operated flights marketed by Delta, customers with a published fare booked in Y, B, M, H, Q, K, L, U, T, X or V class can upgrade into A class (Premium Economy), or they can upgrade from W, S, or A class into Z class (Business Class). In addition, customers traveling on an Air France-operated, Delta-marketed flight and booked in P, A, or G class can upgrade to Z class (Business Class). "

NOTE: GUC usage on AF used to be restricted to high fare classes only. Phone agents may not be familiar with the new rules, and may need to be gently pointed in the direction of the DL T&C on their own website.

NOTE 2: Most of the bullet points about GUCs on KL (above) apply to AF as well, including the advice to get the ticket reissued immediately upon clearing.

Using upgrades on Virgin Atlantic

3-year-old thread: https://www.flyertalk.com/forum/delt...lantic-vs.html
related, upgrading VS with SkyMiles (also requires G class, so the info may be useful too?): https://www.flyertalk.com/forum/delt...pgrade-vs.html

• "Valid on Delta-marketed, Virgin Atlantic-operated flights for use globally on published fares booked in W, S, Y, B, M, H, Q, K, L, U, T, X or V class to Virgin Atlantic’s P class (Premium Economy), or from fares booked in P, A, G class to Virgin Atlantic’s G class (Upper Class)." Upgrading on Virgin-marketed (VS flight number) flights using GUCs is not possible.
• Global Upgrades on Virgin Atlantic flights must be confirmed 24 hours prior to departure.
• Global Upgrade Certificates may not be used to waitlist for a Virgin Atlantic-operated flight. Many agents will offer to put you on the waitlist, but putting you on the upgrade waitlist for a Virgin Atlantic flight will simply never clear so you're better off monitoring it yourself (see next bullets).
• DL flight numbers are not available for most Virgin Atlantic flights to regions other than the US (for example LHR-JNB), so it is not possible to use GUCs on those flights.
• Virgin Atlantic upgrade space appears to use the same availability as awards, so if a business class award is available for a Virgin Atlantic flight on Delta.com, it should be available for an upgrade (as long as that flight is booked on a DL flight number). If an award is not available, an upgrade is probably not available -- but if you notice any exceptions to this rule please share in the thread. You can also monitor G space using ExpertFlyer (see KLM section above).
• Because G is the same code as Virgin Atlantic uses for award tickets, after you fly the tickets will register with Delta as having been awards and will not earn any miles. Watch your mileage earning carefully and you will likely have to call Delta and explain that it wasn't an award ticket but an upgrade from a paid coach ticket, and they will correct the mileage earning to be equivalent to what you would have earned on your original coach ticket.

Using upgrades on Korean (restricted to certain fare classes only)

Dedicated thread: https://www.flyertalk.com/forum/delt...ed-thread.html

"Valid on Delta-marketed, Korean Air-operated flights for use globally on Delta's published fares booked in J class to Korean Air’s A class, Y or B class to Korean Air's Z class, or booked in M class to Korean Air's O class."

GUC usage on Korean requires the purchase of high fare classes, which may mean that it is cheaper to buy a discounted business class ticket than to buy an eligible coach fare and try to upgrade. Uniquely, it is possible to use GUCs to upgrade from business to first on Korean, but only if you buy the most expensive business class fares.

Using upgrades on Aeromexico

"For travel on Aeromexico operated, Delta marketed flights this certificate may be used to upgrade on Delta`s published fares booked in W, Y, B, M, H, Q, K, L, U, T, X or V class and all fare classes upgrade into Aeromexico`s O class."

Using upgrades on Virgin Australia

Valid on Delta-marketed, Virgin Australia-operated flights on published fares booked in Y, B, M, H, Q, K, L, U class to Virgin Australia’s Business Class.

Delta no longer partners with Virgin Australia. "Effective September 1, 2021 Global Upgrade Certificates will no longer be issued on Delta-marketed, Virgin Australia-operated flights. For Global Upgrade Certificates already issued, travel must be completed by August 31, 2022 or within 1 year of the ticket being issued."