Microsoft is now testing Windows 10 build 17629 internally. The new Windows 10 Redstone 5 build 17629 (10.0.17629.1000 rs_prerelease.180318-0044) was compiled on March 18, 2018.
Windows 10 Redstone 5 preview build 17623 is now available for Skip ahead Insiders. The new build has added a High Efficiency Image File Format (HEIF) for Windows 10 and the Photos app.
This build also introduced a safe remove experience for external GPUs connected via Thunderbolt 3. The safe remove experience allows you to know which applications are running on an external GPU so that you can safely remove to prevent data loss during detach.
The ISO files for Windows 10 build 17623 are also now available for download. You can download it from the link below.