In some ways, using Delta GUCs on KLM represents the best deal in travel for Delta Diamonds. I wanted to share my experiences booking this that might help others trying to figure it out.

What are Delta GUCs?

A “GUC” is a Global Upgrade Certificate, which is offered to Delta Diamonds as a potential benefit for qualifying for the status. You’re able to select up to four GUCs in one year, which can be used either for yourself or for others. Think of it as a way to book a cheaper flight and get a space-available upgrade to business class on Delta or on select partner airlines.

Thanks to my rollover MQMs (no longer available) and Delta flights that I’ve taken in 2024, I earned Diamond status.

I don’t expect this to last forever where economy flights can be upgraded to business class on KLM flights. KLM continues to roll out more planes with premium economy and Delta has required that GUCs used on Delta, Air France, and Virgin Atlantic flights can only be used on premium economy tickets for those business class upgrades. Who knows when the rules will change, but I wouldn’t sit on it if you’re a Delta Diamond and you want a cheaper upgrade.

Upgrade rules for KLM flights

You could use your Delta miles to purchase the flight on KLM metal, but I’m more interested in purchasing the flight with cash on KLM’s website. Why? Because when I was digging around, I found cheaper prices just straight up purchasing the flight from KLM than purchasing it via a Delta codeshare. There’s also the case of how the flight credits, which I touch on later in this post.

You’ll find the appropriate terms on the Delta website (emphasis mine).

7. Applicable Fare Classes:  Certificate may be used to upgrade on Delta Air Lines or a valid carrier (as specified above) on published retail fares booked in P, A, G, S, W, Y, B, M, H, Q, K, L, U, T, X or V class and upgrade into RV/OK/OV class on Delta operated flights, and may also be used to upgrade on Award Travel tickets and Miles + Cash tickets on Delta-operated flights, Pay with Miles tickets and Companion Certificates. Certificate may not be used to upgrade other published fares including those booked in Basic Economy. 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.

The thing to note here is that for KLM flights, economy flights (including deeply discounted economy fare classes) are eligible to upgrade into Z class (business). But if you want to upgrade, you’re going to need to make sure that Z class is available for your preferred flight. Note that you need to buy this flight with cash; you cannot book it with partner miles and expect an upgrade from Delta.

Finding the right upgrade space

The conventional wisdom is to go out to Expert Flyer and enter your details. Let’s say we’re looking for a flight from Las Vegas, Nevada to Amsterdam, Netherlands on November 22, 2025 and you want to upgrade a party of 4. On Expert Flyer, just make your way over to the “Awards & Upgrades” button along the left and enter your departure and arrival airports and the date of travel. Under the Airline section, choose KLM and then click the “Business – Upgrade with DL SWU/Global Upgrades & Fare Class (Z)” checkbox.

What you’ll get back is any availability in Z class for that particular flight. In this case, there are 9 seats available, which works for me since I’m interested in 4 seats. Based on my conversations with Delta employees, this is the same amount of upgrade space they see on their end.

Is Expert Flyer actually needed?

So, let me ask a simple question: is Expert Flyer actually needed to determine the amount of upgrade space available? I ask this because Expert Flyer is a subscription-based model (unless you’re using a free trial) and I would like to not pay for an extra service that isn’t needed. Who wouldn’t want to save some money?

I believe potentially you can get around subscribing for it. Go to the Delta website and search for cash fares on the route you’re interested in with the number of passengers you want to upgrade. You should find the same flight (though listed with a Delta codeshare so the flight number won’t be the same) and next to the names of each fare bucket, you’ll find the corresponding fare class. If you see “Z” listed next to Business, you should be golden.

Booking the flight on KLM’s website

Go ahead and enter your details onto the KLM website and take a look at the fares. You’ll see plenty of economy options to choose from, but what counts as the right fare class?

To see the fare basis, choose an option (here I chose the cheapest “Light” fare) and move on to the next screen. Then select the “View trip details and ticket conditions” button.

You’ll find a pop-up that explains more details on the flight. In particular, we’re most interested in that fare basis code. The first letter of that code corresponds to the fare class (in this case, Q). Reviewing the fare classes against the list of eligible fares as stated from Delta will tell you if this works as a starting point for your GUC upgrade (in this case, it works).

Don’t trust what you’re seeing? You can also check out ITA Matrix to see what it says there. Click on the price (in pink) to find out the details of this particular flight.

You’ll see the confirmation not only of the fare class (Q) but also of the fare basis (QKW99NBP) that serves as confirmation for you that everything lines up. Don’t worry that the listed price is slightly different than what we saw on KLM’s website.

I’ll admit that I had some hesitation that a fare on KLM’s website listed as “Light” economy would count as qualifying for an upgrade given issues that surround basic economy, but I’ve found that as long as the fare class falls into the correct buckets, it’s fine to choose a “Light” fare. Feel free to proceed to purchase on KLM’s website at this point.

As a bit of confirmation, booking on the KLM website would cost $3,580 for this particular date in Q class for a party of 4. If you book on the Delta website (meaning booking as a Delta codeshare), Q class is not available and instead you need to book in L class, which would have cost $4,180 for the same party of 4, or $600 more than booking on the KLM website.

Calling in to book the upgrade

This is where the process slowed down for me. There wasn’t a wait for me to get in touch with an agent when calling the Diamond line, which was great, but I found a couple of agents who haven’t had experience with booking GUCs on KLM-issued tickets.

The first agent I talked to mentioned that while she saw upgrade space existed, the reservation appeared locked on her end and wouldn’t be able to do anything for me. I believe she didn’t realize she needed to recreate the ticket in order to process the upgrade and it didn’t sound like she was interested in learning the process, so I thanked her for her time and hung up.

The second agent stated that I was incorrect–that only Delta-issued tickets would be eligible for upgrades via GUC. I could have hung up at this point, but decided to push back and mention that Delta’s website states KLM-issued tickets are eligible. He admitted he was incorrect and then said he would need to contact his ticketing partners to research how to book this since he has never done it before (success!). It took nearly 40 minutes on the phone for it to be ticketed, but it does indeed work. It’s just a bit of a pain for the agents since they need to recreate it on their end. It would have been an easier process for Delta agents if you booked a Delta codeshare right from the start (of course in this case you would have overpaid).

How do flights credit?

Beyond the cheaper price up front, it gets fairly interesting on the earning side of the house too. If you book a Delta codeshare, expect to earn miles and MQD based on the price of the ticket. On Delta’s booking page, you can see it as earning 11,132 redeemable miles (as a Diamond) and $1,012 MQDs.

But what about a KLM-issued and KLM-operated ticket? That follows a different scale based on the length of the flight.

This particular route between Las Vegas and Amsterdam is 5,355 miles in length. Booking the ticket with KLM moves you into the Z revenue bucket, allowing you to earn 200% miles as redeemable (plus a 120% Diamond Medallion bonus) and 30% of the length counts as MQD. That translates to $1,606 in MQD (5,355 x 30%) and 17,136 redeemable miles, a nice boost over Delta’s earn rate for Delta codeshares. It’s nice that using GUCs helps earn more rewards by booking partner flights on partner ticket stock.

We could have done even better if we found a cheaper one-way flight to Europe, but this was ultimately just a simple example of the process.