Microsoft isn't yet done developing Windows 10 19H1 (also expected to be known as the April 2019 update/1903). But on February 14, the Windows 10 team released to testers in the "Skip Ahead" ring a new test build which they said comes from the Windows 10 20H1 development branch.
Build 18836 is not from the Windows 10 19H2 (October 2019/1909) branch, as one would expect. Microsoft officials said today that they plan to begin releasing 19H2 test bits to Insider testers "later this spring."
Officials didn't say much about the reasons for the unusual move of jumping ahead to the 20H1 branch beyond "some things we are working on in 20H1 require a longer lead time."
I asked on Twitter whether today's test build is different from the 18834 Windows 10 19H1 test build which Microsoft released last week. Senior Program Manager Brandon LeBlanc responded:
"Right now 20H1 and 19H1 builds are largely the same and haven't diverged too much yet in terms of code. It'll be a little bit before they do. Eventually, 20H1 builds will start seeing a behind-the-scenes changes etc."
The list of changes and fixes in today's 18836 build which Microsoft disclosed in its February 14 blog post are for issues that were found in Windows 10 19H1. Microsoft officials didn't call out any features that will be new to Windows 10 20H1. Usually, when Microsoft releases its first few new Skip Ahead builds, those test releases include some under-the-covers updates to the Windows 10 core and not any noticeable new features.
If Microsoft continues along its current development path, Windows 10 19H1 should start rolling out to mainstream users in April 2019. Windows 10 19H2 should be out in October 2019. And Windows 10 20H1 should begin rolling out to mainstream users in April 2020.
Some of my Microsoft-watching colleagues on Twitter are wondering whether Microsoft is planning to modify its testing rings, given today's announcement.
Maybe Microsoft will release Windows 10 19H2 test builds only to Fast Ring testers and not Skip Ahead ones? In other words, perhaps Skip Ahead testers will actually be testing new feature releases that are further out from delivery? Such a change might make sense and could potentially be a way for the company to shore up its testing process so there isn't another Windows 10 1809/October 2018-type update debacle. But for now, these are just guesses, not official testing changes.
Update: LeBlanc tweeted that once a tester takes a Skip Ahead 20H1 build, s/he can't downgrade. This basically means that only Fast Ring (and, I'd assume, ultimately Slow Ring/Release Preview Ring) testers will get Windows 10 19H2 test builds. It doesn't necessarily mean that Fast/Slow/Release Preview Rings won't ever get 20H1 builds, however.