Usually with soak tests they send out an email inviting you to sign up to participate and then you get an email several days later telling you that the update is coming, so I assume that we'll start hearing about what the update actually is by Friday, maybe, or early next week, if the past is any predictor. Usually somebody leaks what the test is - when the software rolls out, we'll know it within an hour or two.
I assume that they are using a small number of people for the soak this time, since a lot of people who did soak tests before say that they didn't get an email. After the bricking the last time, that sounds like a pretty smart plan to me.