https://wccftech.com/want-ios-12-gm-before-anyone-else-then-take-these-measures-right-now/

We know you’ll want iOS 12 GM (Gold Master) way before anyone else come September 12, so take these measures right now.

As is the case every single year, Apple is going to release iOS 12 GM to developers and testers before pushing the update out to everyone else later this year. This is done so that last minute bugs are ironed out in case they manifest in any way. But usually, the GM build is seeded as-is to everyone at a later date and it’s rare that Apple runs into a slight hiccup.