The Great Vault is a weekly reward for raiding, doing Mythic+, and PvP. You can read more about it here: https://blog.askmrrobot.com/how-the-great-vault-works/
The Great Vault Upgrade Finder search will help you decide which reward to take.
Import your Rewards
As long as you have version 96 or later of our in-game addon, we will automatically read your available rewards every time you export your character. So when you have rewards available, simply export your character as normal, and you will see a list of your potential rewards in the options for the Great Vault search.
Add to my Bag
We have also added another search called “Add to my Bag” (if you don’t see it yet, it will be live within a day or two of this post). It ranks gear exactly the same as the Great Vault search, but allows you to manually pick the items to rank rather than importing your rewards for the week.
We do a ranking that is slightly different than our other Upgrade Finder searches, and more thorough. Because the potential rewards are a very small list of items (no more than 9 each week), we can do a complete Best in Bags optimization to find the best possible reward. For rewards that are not the best, we do a slightly faster Best in Bags optimization to give them a good ranking relative to the best reward for you that week.
For example, if you have 3 potential rewards:
We run Best in Bags as if you own all of the rewards (making sure to only allow the optimizer to choose one of those rewards, since you can only get one). The score of the top-ranked item will exactly match your Best in Bags score were you to choose that as your reward.
For the other two items that aren’t the best, we lock them in place and do a quicker Best in Bags optimization to get a good ranking for them. Were you to pick one of these items as your reward and run Best in Bags, your final score might not exactly match what the Upgrade Finder showed, but it will be extremely close.
The reason that we do this is that running a complete Best in Bags optimization for multiple items would be very slow (up to 9 rewards, so worst case it could take 9 times longer than a normal Best in Bags optimization). But using this hybrid approach gets very close to the same result in a much shorter amount of time, and without compromising the most important piece of information: the ranking of the best available reward.