It's the closest thing we have to the old "Semi-Annual Channel" and "Current Branch for Business."
In the past few hours, Microsoft has given its deployment go-ahead for Windows 10 version 1903, putting it in the CBB/SAC/”ready for broad deployment” branch. The Windows 10 release information page now says:
Current status as of September 26, 2019:
Windows 10, version 1903 (the May 2019 Update) is designated ready for broad deployment for all users via Windows Update.
As devices running the Home, Pro, and Pro for Workstation editions of Windows 10, version 1803 (the April 2018 Update) will reach end of service on November 12, 2019, we are broadly updating these devices, as well as those running earlier versions of Windows 10 that are past end of service, to keep these devices both supported and receiving monthly updates. If you are not offered the Windows 10, version 1903 feature update, please check below for known issues and safeguard holds that may affect your device.
We recommend commercial customers running earlier versions of Windows 10 begin broad deployments of Windows 10, version 1903 in their organizations.
From where I sit, that's horsefeathers. The first cumulative update for September – lthe atest "non-optional" build of Win10 1903, 18362.356 – has several known problems, including the acknowledged audio level bug.
[ Further reading: Windows 10 October 2018 update: Key enterprise features ]
The spectacularly mishandled second cumulative update for September, build 18362.357, introduced several new bugs – and was never distributed through the normal update channels.
Win10 version 1903’s third September cumulative update, released yesterday, build 18362.387 – billed as an “optional non-security update” that nonetheless includes a hastily assembled security patch – has at least two well-documented bugs (preventing installation of .NET 3.5 and driving certain HP printers nuts). Microsoft hasn’t yet acknowledged those bugs, but it’d be kind of unseemly to admit to embarrassing problems on the same day that the version is elevated to CBB/SAC/”ready for broad deployment” status.
Admins I know are livid about the ridiculous (non) rollout of the CVE-2019-1367 Internet Explorer “0day” patch and its bumbling aftermath. I can’t wait until they stumble into work this morning and discover that Microsoft is telling them (and their managers) that they're ready to roll version 1903 out to the masses.
The obvious impetus: Microsoft intends to push out Windows 10 version 1909 shortly, so it needs to tie up loose ends with 1903. This announcement has nothing to do with 1903’s stability, and everything to do with Microsoft’s distribution calendar.