Didn't get a chance to dig into Sea of Thieves when the closed beta came around? You're about to have another chance. Sea of Thieves is getting a new scale test in order to test the limits of the servers. The scale test is going to be coming up this weekend, starting on February 16th, and going until February 18th.
The test is not going to be focused on adding in new features, or even trying to root out bugs. Rare is just trying to get as many people playing at the same time as they possibly can, in order to get an idea of how many users they can fit in. If you had access to the closed beta a few weeks ago, you automatically have access to this - so be sure to mark your calendar and log in as much as you can to help out the test!