Microsoft is now testing Windows 10 build 17129 internally. The new Windows 10 build 17129 (10.0.17129.1 rs4_prerelease.180319-1403) was compiled on March 19, 2018.
Windows 10 Spring Update preview build 17127 is now available for Insiders which comes with Cortana improvements. A new server-powered profile page is now added in Cortana to add and edit your favorite places. The places you add are used to give you traffic updates for your daily commute, and let you easily set reminders when you arrive or leave your places.
Windows 10 build 17127 ISO images are also now available for download. You can download it from the link below. The final Windows 10 Spring Update will release in April for everyone.