Right up until September 30th, the rumor mill churned with tidbits of info regarding what we all expected would be called Windows 9. What follows is our collection and informed opinions on all the rumors and leaks leading up to the unveiling of Windows 10. Enjoy!

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.

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; Windows 8.3 though is likely to be a non-starter. 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.

While still just a codename, Windows 9 was referenced by Microsoft in a job posting, spotted by MSFT Kitchenon March 13, 2013 and a senior Microsoft VP let the name slip during a live-stream presentation.

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 alluding to the shift from our reliance on the traditional desktop to a new world where the Start screen is at the heart of how we use Windows.

The term "Windows TH" (possibly for Threshold) appeared on Microsoft's website, referring to a technical preview, before being removed, just days before the September 30th event.

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

As of right now, we expect to see Windows 9 in a preview build (otherwise known as Windows Technical preview) to appear on September 30. The latest report from The Verge and Recode cite sources close to the matter with knowledge that a press preview event will take place on that date.

Recode's Ina Fried said that the event - geared towards developers and an enterprise audience - will take place in San Francisco with our own sources confirming that invites have apparently gone to relevant media houses and tech analysts.

Microsoft has confirmed that it won't be live streaming the event. The company has sent a statement to Winbeta.org stating that "There will be no live stream of the keynote" although one can expect news and content to be posted across all of Microsoft's MSDN blogs.

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 to coincide with the back-to-school season and in time for the lucrative holidays season.

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. They also mentioned that upgrading from Windows 7 to Windows 9 would cost you about $30 or £20, which is sounds pretty reasonable.

What the collective has heard exactly is that a prototype version is in the works in which a barebone 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.

Microsoft has learnt to be flexible though given the changing business environment. Google's Chrome OS was barely a blip on Microsoft's radar when Windows 8 launched. Now it is seen as a growing threat to Microsoft's low-end market, so much so that it is giving Windows 8.1 for free on devices sporting an 8-inch (or smaller) display.

It is very likely that Microsoft will do the same for Windows 9 (although it could also choose to keep Windows 9 as a premium SKU). Last but not least, the president of Microsoft Indonesia has inadvertently disclosed that Windows 9 would be free for Windows 8 users.