This will depend on when you get through the queue and into actual registration. But the 10k is one of the first things to sell out.
10k first, then the marathon. Explanation below.
Start here. DopeyBadger has kept tabs on the race sellouts, and once you factor in anniversary weekends, you can generally see the trends. If you go through that thread, there are also
several posts with pictures of what the registration page will look like, what information you'll need to know (especially important if you are registering other people.) It's really helpful.
There are no anniversaries for MW in 2026, so "normal" sell-outs should happen in their usual order of 5k first, then 10k or Goofy 2nd and 3rd. Then Dopey, and followed by either the HM or M.
If one of the races is the "MUST-DO" and the other "I'm ok if I miss out" then complete your registration for the must-do registration and PAY FOR IT.
Once you do that, you can go right back in
using the same browser and register for another race. While I personally haven't done this, there are plenty in here that have and should not end up in the queue, but get put directly into the registration page because they base it off your browser ID.
If you feel more "ALL OR NOTHING" about the registrations, fill out the first one, click "add another registration" (or whatever the wording is) and then complete the 2nd/3rd/4th registration(s) and pay all in one transaction. If something sells out, I believe you have to start completely over. Your cart contents are not "held" while you are completing the registrations and checking out.
If you get a short queue that you can start the registration process within 30-40min of it opening, I would do it all in one transaction. After that 30-40min I would check out with the one that usually sells out sooner and then go back for the 2nd in a separate transaction.
The usual method for us is to have as many devices/browsers available to us open
before 10am. As soon as the first distance "register now" button pops up, we start clicking on it because all users who enter the queue before 10am (or when they open registration...it's not always right AT 10am) will be placed in random order, and all users who join AFTER are placed in the order in which they join. That means I have my computer with 2 different browsers both with normal and incognito open. That's 4. Then my phone with 1 normal and 1 incognito. And so on with whatever devices I have at my disposal. Some of us will stagger when we join, or join the queue right when it goes live, but it's really just random of where you will get placed. If you end up with extra queue IDs that are counting down, we share them with other dis'ers via DM. This is generally pretty successful, but as always YMMV because we don't know when rundisney will change something on their end and they could possibly tie a queue ID to your login or something.