https://wccftech.com/windows-10-1903-finally-makes-its-way-to-slow-ring/

Microsoft usually starts shipping out Insider Preview Builds to the Slow ring after the first few builds make their way to the Fast ring. However, those in the Slow ring continued to wait for the upcoming Windows 10 1903 (19H1 branch) builds despite the development process having almost reached the finish line. That changes today as the Windows maker has made the first Preview Build for the Slow ring available today.

Windows 10 Insider Preview Build 18342 was released to the Fast ring last week. Insider Preview Build 18342.8 is now available to those in the Slow ring who choose to avoid dealing with the initial bug-infested builds.