Windows 10 build 17615 is now going through internal testing. The new Windows 10 Redstone 5 build 17615 (10.0.17615.1000 rs4_prerelease.180227-1457) was compiled on Fab 27, 2018.
Previously, Redstone 5 build 17604 was released for Skip ahead insiders. Read more details here.
Windows 10 Spring Update preview build 17110 is now available for Insiders. The new build comes with improvements for Enterprise Customers as well as added various bug fixes.
The ISO files for Windows 10 build 17107 are also now available for download. You can download it from the link below.