Apple has released the golden master of iOS 13 to developers, as well as the third developer betas of iOS 13.1 and iPadOS 13.1, as well as a 10th beta version tvOS 13. 

Registered developers can download the betas via Apple’s developer portal (https://developer.apple.com/account/#/welcome). Or they can be downloaded over-the-air once the proper configuration profile has been installed from the Developer Center.