Microsoft announced yesterday that Slow ring members of the Windows Insider Program were being moved over to the Windows 10 20H1 development branch. That means almost all of the company's pre-release testers are using the next major version of Windows 10, which is expected to arrive during the first half of 2020.
Slow ring members shouldn't have been too surprised by this change. Microsoft said multiple times that it was moving them to the Windows 10 20H1 development branch, and even though it did so by updating an existing blog post several times rather than publishing new ones, word about its plans quickly got around.
The company did actually publish a new blog post yesterday, which made the update to Windows 10 Insider Preview Build 19013 that much easier to see coming. Anyone who didn't want to jump from Windows 10 19H2 (which should be released to all Windows 10 users soon) to Windows 10 20H1 had plenty of warning.
This change doesn't mean a whole lot in and of itself. Microsoft said that Preview Build 19013 "includes a fix for the issue where the Settings app would hang or crash when accessing the System or Ease of Access sections." End description of the changes Slow ring members can expect as they move between dev branches.
Windows 10 20H1's spread throughout the Windows Insider Program should indicate that its development's on track, though, and that's probably the only sign we'll get until the update gets closer to release. Microsoft doesn't tend to offer specific release dates for these updates until just before they become available.