Update: It looks like Windows 9 will fundamentally transform not just the PC operating system, but all of Microsoft's OSes. Head over to Page 2 to read up on the latest news and rumors!

With Windows 8 and now Windows 8.1, Microsoft tried – not entirely successfully – to make tablets part of a continuum that goes from number-crunching workstations and high-end gaming rigs through all-in-one touchscreen media systems and thin-and light notebooks down to slender touch tablets.

The general consensus is that it still has a long way to go to produce a unified OS.

Despite rumors of an aggressive development and shipping schedule, there's no official word about what's in the next version of Windows, but there are plenty of rumors (many of them from Chinese enthusiast sites that claim to have leaked builds), plus more reliable information from job postings for the Windows and Windows Phone teams.

There are also patents, which may or may not be relevant, and some rare comments from developers on the Windows team. Here's what we've heard about Windows 9 and what we think is happening.

Cut to the chase
What is it? A complete update of Windows
When is it out? We expect it to be out in 2015
What will it cost? We really have no idea. But if Windows 8 is anything to go by, it won't cost much to upgrade.

Windows Blue turned out to be Windows 8.1 rather than a completely new version of the Windows OS – Windows 9 will be that new version.

As for interim releases, we'll probably also get Windows 8.2 before we get Windows 9. And we have already seen the initial update to Windows 8.1, called Windows 8.1 Update 1.

Windows 8.1 Update 1

The new update features improvements to the Start Screen including the ability to boot straight into the Desktop, the return of shutdown on Start and a more familiar task bar to unify the old and new user interfaces. The update was announced at Build 2014, along with features teased for Windows updates to come.

It certainly seems there's a new development cadence for Windows in action. It seems that Microsoft is set to put out new releases of Windows, Windows RT and Windows Server every year, the way it already does for Windows Phone.

The next complete version of Windows is being referred to as Windows 9, though this may change. And a new codename has appeared – Threshold, possibly in refrence to moving across from our reliance on the desktop to a new world where the Start screen is at the heart of how we use Windows.

While still just a codename, Windows 9 was referenced by Microsoft in a job posting, spotted by MSFT Kitchen on March 13, 2013.

The ad, for a Bing Software Development Engineer, says that the team will be delivering products "in areas including Windows 9, IE11 services integration, touch friendly devices including iPad and more."

Windows 9 release date

Microsoft communications chief Frank Shaw said the company wasn't ready to talk about how often Windows might come out when we spoke to him in January, but he agreed "you have certainly seen across a variety of our products a cadence that looks like that; Windows Phone is a good for example of that, our services are a good example of that".

We don't know if Windows 9 will be available as an upgrade from Windows 7 that you can buy as a standalone product or if you'll have to have Windows 8 to get the upgrade. But it may not be with us for a while yet – Windows business chief Tami Reller has talked about "multiple selling seasons" for Windows 8, meaning that we'll likely have several versions of it.

Some rumors have suggested late 2014 or early 2015 for a Windows 9 release, though the former seems wide of the mark. While claims and reports are all over the place, it seems like Windows 9 should drop before September 2015 at the latest.

In January 2014, well-known Microsoft blogger Paul Thurrott said he believes the company plans to release Windows 9 (codenamed Threshold) in April 2015, less than three years after Windows 8.

The thinking appears to be that the Windows 8 name is now too tarnished and that – in contrast to Reller's comments above – Microsoft wishes to clear things out by releasing Windows 9 instead.

ZDNet's Mary Jo Foley recently echoed these reports, citing sources pointing toward a spring 2015 release for Windows 9.

In May, prolific Microsoft leaker FaiKee released two separate documents that he or she claims to be Redmond's full roadmap for Windows 9 and other products. The first of which, released to the My Digital Life forums, pointed to text reading "Windows 9 Windows Preview Release @ 2015 02-03."

That appears to point toward a preview release of either February or March 2015. The second leak was caught by Myce.com, and is a bit more vague in timing but less so in the actual text. That alleged official document detailed a preview release between Q2 and Q3 2015, so by September of next year at the latest.

In June, we learned from a ZDNet source that Microsoft would launch a preview build of the latest Windows in the fall. But most recently, WZOR struck again with a rumor that Windows 9 in full will launch in that same time frame. Naturally, a Microsoft representative snapped back at the rumor on Twitter.

How much will Windows 9 cost?

Not a cent. At least that's what Russian leaker collective WZOR claims to have heard. The group reports that Microsoft is considering pushing out Windows 9 for free, but cannot confirm at this time.

What the collective has heard exactly is that a prototype version is in the works in which a barebones version of Windows 9 will be available for free. For additional functionality, users would have to pay up through a subscription.

That said, ZDNet's Foley has heard the opposite: different SKUs of Windows will be offered for free or at different prices to OEMs and consumers, but that the desktop version will indeed have a sticker price. A recent, subsequent leak provided by WZOR seems to not only corroborate Foley's sources, but render its previous report moot.