Apple instantly releases iOS 11.4.1 Beta 2 to registered Developers with a build number 15G5063b & just after the release of iOS 11.4.1.
iOS 11.4.1 beta 2 contains security with bug fixes and improvements.
Downloading iOS 11.4.1 beta 2
The registered developer can download the iOS 11.4.1 beta 2 from the Apple Developer Program with an appropriate configuration profile or Apple Beta Software Program through Settings >> Software Update >> Download and Install.
Along with that Apple also releases second betas of macOS 10.13.6 and tvOS 11.4.1.
Image Credit: Apple