Is this one of those situations where we sign up and get a bit of money from the company, or will we have already been contacted?
Amazon will do an automatic payout to some people for up to $51. No need to claim anything for that. I'm guessing they'll mail checks or prepaid debit cards or something.
Then Amazon will make a website, within 30 days, and post it on their site (and I'm sure news media will also post it) that will be for manual claims. These claims are also for up to $51 and people will have 180 days to manually claim.
After that, if there's still money, then Amazon will repeatedly do more $51 automatic payments to more people until they're out of money (basically more lax automatic qualification of Prime members from June 23, 2019 to June 23, 2025).
Basically ~30 million people get up to $51.
[0] https://www.ftc.gov/system/files/ftc_gov/pdf/Amazon-ROSCA-Or...