This build is an internal build with the same build number as the released version of iOS 12.0.1 It was first found on an iPhone XS Prototype (likely PVTe based on last digits of serial number and manufacture date). This build is overall very similar to 16B92.
This build has a kernel version of Darwin Kernel Version 18.0.0: Tue Aug 14 22:08:36 PDT 2018; root:xnu_development-4903.202.2~1/DEVELOPMENT_ARM64_T8020