On April 18, some tech pros began noticing that Microsoft had made its Windows 10 1903/May 2019 Update release available on MSDN for download. If Microsoft hadn't changed its Windows 10 servicing cadence a couple weeks ago, this would be business as usual. But, in early April, Microsoft officials said the plan was to make Windows 10 1903/May Update available to consumers and business users starting in late May, not in mid-April.
From Microsoft's April 4 blog post about plans to change the Windows 10 update experience in the name of improved quality:
"Our commercial customers can begin their targeted deployments in late May, which will mark the beginning of the 18-month servicing period for Windows 10, version 1903 in the Semi-Annual Channel. We recommend IT administrators start validating the apps, devices and infrastructure used by their organizations at that time to ensure that they work well with this release before broadly deploying. The May 2019 Update will be available in late May through Windows Server Update Services (WSUS), Windows Update for Business, the Volume Licensing Service Center (VLSC) for phased deployment using System Center Configuration Manager or other systems management software."
Microsoft's plans for 1903 was to give the "RTM" bits longer to bake in the Windows Insider Release Preview ring, as well as inside Microsoft, its OEM, and ISV partners before making the new bits available to mainstream customers. Microsoft pushed out the Windows 10 1903/May Update bits to Insider testers in Release Preview on April 8.
Officials said earlier this month that business customers would be able to start testing the commercially available 1903/May update internally in late May, and that Microsoft would use the late May date when it begins rollout as the start of the 18-month support period for Windows 10 1903.
Yet now, on April 18, Windows 10 1903/May Update (Build 18362.30) and its Windows Server 1903 complement both showed up on MSDN for download, as noted by Tero Alhonen and WZor.NET on Twitter. The 1903/May Update bits are not yet available in the Evaluation Center or VLSC.
I contacted Microsoft officials to see if this was a mistake on its part or if Microsoft intended to make the coming release available a month or so ahead of schedule for those with MSDN subscriptions. Or maybe Microsoft's (unstated) intention was to get IT pros to start kicking the tires of the near-final Windows 10 1903/May Update in a controlled-pilot kind of way by putting the bits on MSDN? So far, no response form Microsoft on this.
Update: It's increasingly looking like this was not a mistake, but intentional. In early April, Microsoft officials never shared when they planned to release the 1903/May Update bits on MSDN. In the past, Microsoft usually released RTM bits to MSDN around the same time they went to VLSC and other "mainstream" business channels. But it looks like Microsoft is going with the literal definition of MSDN -- Microsoft Developer Network -- and not looking at it as a business/IT pro channel. And so 1903's release on MSDN is tied to the SDK release today.
Microsoft released the Windows 10 Software Development Kit (SDK) for the May 2019 Update on April 18 with a "go-live" license and told developers they could start developing on the Windows 10 May 2019 Update now.