Microsoft rolled out its first test build of its spring 2019 feature update for Windows 10 on July 25.
Officially codenamed as "19H1" for "first half of 2019, as previously rumored-- rather than as "Redstone 6," in keeping with previous codename patterns -- today's test build is the first Skip Ahead Ring build for the upcoming release. (The build number for Skip Ahead is 18204.)
Microsoft also rolled out another Windows 10 "Redstone 5" test build today to those in the Fast Ring. The build number for the Fast Ring build is 17723.
The feature set for 17723 and 18204 is the same at this point; Microsoft is just establishing a baseline for the next Windows 10 feature update by splitting the two branches.
There are a few, new relatively minor features in 18204 and 17723.
A new "Mixed Reality Flashlight" for mixed reality testers will allow them to open a portal into their real world via the Start menu, a button shortcut or voice command. Microsoft is billing the feature as a way "to mix your physical and virtual realities."
Both of today's test builds also add support for new Group Policies for Microsoft Edge. These policies include the ability to enable/disable full-screen mode, printing, favorites bar and saving history; the ability to prevent certificate error overrides; the ability to configure the Home button and startup options; setting the NewTab and home button URL; and managing extensions.
Today's test builds also add support for leap seconds, a new time protocol called the Precision Time Protocol and software timestamping. And with today's builds, Microsoft is adding a new trained model design to more accurately predict when the right time is to restart a device in the name of improving the update experience.
Windows 10 19H1 is expected to begin rolling out to mainstream users starting around May 2019, as long as the company is sticking with its previous feature-update rollout schedule.
There are a lot of fixes across all aspects of Windows 10 in today's builds, as well as a known issue for developers around switching to the Slow Ring. Microsoft's blog post about today's builds has all the details.