Microsoft has scaled back its Windows 10 release schedule to two feature upgrades annually, not the three per year it once said was its plan.

The Redmond, Wash. company has hinted since November that it would cut back on the number of Windows 10 upgrades. That's when it began to refer to the schedule as "two to three times per year," rather than the solid three-times-a-year pace it had talked up before Windows 10's official release.

But in a presentation at the WinHEC technical conference in Taiwan last month, Microsoft provided its hardware partners and third-party developers a more definitive release cadence for Windows 10.

"Targeting twice per year with new capabilities," Microsoft said of Windows 10's servicing strategy in a slide presented by Chris Riggs, senior program manager, as part of a larger deck about "Windows as a Service" (WaaS) -- Microsoft's label for the new maintenance model.

On another slide, Riggs laid out the schedule of each major upgrade: For the first four months after debut, each build will be pushed only to consumers and those businesses that have adopted the faster "Current Branch" (CB) release track.

After its four-month life in the CB, the upgrade will be promoted to the "Current Branch for Business" (CBB), the track that companies are expected to assign to the bulk of their PCs.

That build will be available to deploy and use for the next 12 months, with a 60-day grace period tacked to the end. The grace period gives businesses time to migrate to the next build before Microsoft pulls the patch plug on the predecessor, halting delivery of security updates and other bug fixes.

In total, then, corporate PCs will run each CBB anywhere from 12 to 14 months, with the latter including the 2-month grace period.

Microsoft issued the first Windows 10 upgrade to the CBB in mid-April, about five months -- not four -- after it began appearing on CB-assigned PCs. That build was designated "1511" to mark the year and month of its original launch.

If Microsoft adheres to Riggs' schedule, businesses running Windows 10 1511 on the CBB will generally deploy and use it until April 2017 before beginning to shift to the next upgrade. They must wrap up their move off 1511 and onto its replacement by June 2017, or face a patch spring that's gone dry.

Data: Microsoft The latest lifecycle for Windows 10's November 2015 upgrade, pegged as "1511," puts its end-of-support around June 2017.

The follow-up to 1511, to be designated "1607" to mark its July 2016 release -- according to another WinHEC presentation, it will ship July 29 -- will thus launch about 8 months after 1511 and presumably hit the CBB pool of PCs in late November 2016.

That timeline jibes with Riggs' presentation, as 1607 will reach CBB a year after the former build, 1511, landed on the CB.

Meanwhile, this summer's 1607 build -- which Microsoft has been calling "Anniversary Update" -- would be supported with patches on the CBB track until January 2018.

Data: Microsoft Windows 10 1511's successor, tagged "1607," should hit the Current Branch for Business in November and receive security updates until January 2018.

Confused?

It's actually a bit less bewildering than Microsoft's original timetable for Windows 10, which was to sport three feature upgrades annually, and so have even more builds active at any one time.

There will still be multiple CBB editions active simultaneously, however. Riggs' timeline signaled an overlap between November 2016 and June 2017 when both 1511 and 1607 would be supported with security fixes. If Microsoft were to repeat its upgrade tempo of 2015 this year -- one in July, a second in November -- a smaller window between March 2017 and June 2017 would include three supported builds on the CBB, the latest stamped "1611" to mark its launch date.

The latter seems unlikely.

Speculation has been widespread that Microsoft will only issue one Windows 10 upgrade in 2016, then ship the next in the spring of 2017.

In Riggs' presentation, the word "targeting" in the phrase "Targeting twice per year..." suggested as much; it implied that Microsoft would shoot for two annual upgrades but might not always meet the goal.

The slower Windows 10 upgrade tempo is not completely unexpected. Two months ago, Gartner analyst Steve Kleynhans pointed out that the schedule was in flux, most likely because Microsoft realized it could not meet the original 3x pace, or that corporate customers were balking at a three-time-a-year cadence, or a combination of the two.

At the time, Kleynhans said that if a slower schedule were adopted, "It's because that's what the market has ended up telling Microsoft."

From what Microsoft told partners at WinHEC, it sounds like that market has spoken.

The "Windows as a Service" presentation that Riggs presented at WinHEC can be downloaded from Microsoft's website.