User blog comment:Brandon Rhea/How we're testing the fandom.com domain migration/@comment-24361909-20181006211835/@comment-20644-20181006212429

We're starting with an initial 50 communities on Monday, to see what happens once those domains are migrated. These communities are on the lower end of the traffic compared to other communities in the 3,200, so the risk is much lower for that initial migration. Once we're comfortable with what we see, we'll migrate more.

If all goes well the entire test group will be migrated pretty quickly, but we're allowing ourselves up to 3 weeks in case we need time to adjust anything with the migration.