Microsoft is now testing Windows 10 build 17681 internally. The new Windows 10 Redstone 5 build 17681 (10.0.17681.1000 rs_prerelease.180524-1724) was compiled on May 24, 2018.
Recently, Windows 10 Redstone 5 preview build 17677 was released for Insiders. The latest insider build comes with various bug fixes and improvements. The Windows Security Center (WSC) service now requires antivirus products to run as a protected process to register. Products that have not yet implemented this will not appear in the Windows Security UI, and Windows Defender Antivirus will remain enabled side-by-side with these products.