Microsoft isn't yet talking about the next update to Windows Phone. Though the company has made a series of small updates to Windows Phone 8, with three delivered so far, the platform is more or less the same as it was in 2012.

A big update is, however, in the cards. A series of leaks over the past few weeks have revealed an abundance of details about what Microsoft is likely to call Windows Phone 8.1. Unlike the three updates already made to Windows 8, Windows Phone 8.1 will be huge: so big that the 8.1 name (no doubt chosen to align the phone operating system with the desktop and tablet one) is downright misleading. If version numbers were determined by the scale of changes alone, this would be called Windows Phone 9.

The single biggest leak is the release of a version of the Windows Phone 8.1 SDK, the tooling and documentation that enables developers to produce Windows Phone 8.1 applications. It's unfortunate that this had to leak. Windows Phone 8 was in a similar situation; prior to its launch, the SDK was only distributed to a few select partners. The result was, come launch time, vanishingly few applications actually existed to take advantage of Windows Phone 8's new capabilities.

Such appears to be the case this time around too; a few select partners have been given access to the SDK—and promptly leaked it—but the regular Windows Phone developers are kept in the dark.

In conjunction with other leaks, a reasonably complete picture of Windows Phone 8.1 is available. Some of the details are still in flux, so things like the appearance of all the new features aren't necessarily nailed down, but at this point we have a reasonable grasp of the broader capabilities, and a few important highlights stand out.

8.1 is set to address a lot of missing user features. Some are much-demanded capabilities. Action Center will provide centralized notification management to see historic alerts, missed notifications, and so on, and it will also provide quick access to things like airplane mode. 8.1 will support different volume settings for music and for notifications. Google Calendars with multiple calendars will be supported. There will be a full-featured podcast app.

Other features are of narrower interest, but no less important. Enterprise support is greatly expanded, with VPN support, encrypted S/MIME e-mail, EAP-TLS Wi-Fi authentication, certificate management, and support for scanning and OCRing documents with the camera.

There are also lots of broader system updates: Internet Explorer gets bumped to version 11, including WebGL support and support for the rich YouTube HTML5 experience. A new Battery Sense feature will show which apps are using the most power and allow you to choose which apps get suspended when in battery saver mode. There will be built-in support for Bluetooth LE, mice, keyboards, Miracast, and Wi-Fi Direct.

There will be new ways of interacting with the phone. The keyboard will support swiping, so fingers can be dragged from key to key, and there is expected to be a new virtual assistant along the lines of Apple's Siri, currently named (or perhaps codenamed) Cortana. Personally, I feel that Google Now is a better model to follow, as I've found it manages to be useful more often than not without me even having to ask it.

But more than all this is the behind-the-scenes alignment with "real" Windows. Windows Phone 7 apps were built with, more or less, a version of Silverlight, Microsoft's cut-down .NET framework. Windows Phone 8 apps had a range of options. 7-style Silverlight apps could still be used, but using any new 8 features meant rebuilding with a sort of hybrid system: a derivative of 7's Silverlight-based API, but running on top of the full-size .NET framework. In parallel, native C++ could be used, with access to Direct3D, and a very small subset of the WinRT API that's used for Metro apps in Windows 8.

Windows Phone 8.1 shakes things up radically. It will continue to support the Silverlight-based applications developed for both Windows Phone 7 and Windows Phone 8. It will also provide a new version of Silverlight, dubbed Silverlight 8.1, to give those applications access to some—though not all—of 8.1's new features.

But what Microsoft really wants is for developers to create apps using the Windows Runtime (WinRT). Windows Phone 8.1 will be the first meaningful iteration of Microsoft's converged Windows platform. Developers will be able to write apps using WinRT, and in principle these applications will be universal, able to run both on the phone and on the PC. WinRT applications will have the most extensive access to the underlying APIs and capabilities of the device, and going forward, WinRT is going to be the API that grows and becomes richer.

Just like on desktop Windows, WinRT apps on the phone will be able to use C#, C++, VB, or HTML and JavaScript.

Not all code will be common, with Microsoft estimating that perhaps 20 percent, especially around the user interface, will need to be custom work to handle the different form factors. Nonetheless, the release of Windows Phone 8.1 means that Windows will finally be in a position comparable to iOS and Android. Those platforms both allow mobile developers to relatively easily target both phone users and tablet users with substantially the same code.

Even with 8.1, the platforms aren't fully unified. Windows Phone, for example, has richer control over data usage and background downloads than Windows does. Some applications will need to continue to use Silverlight 8.1, too; WinRT doesn't support the Windows Phone VoIP API, or the Camera Lens API, or a few other bits and pieces. Windows has a charm concept for sharing between apps with no counterpart in Windows Phone. So while the long-term story for developers is a good one, it does mean that they'll be targeting another interim platform in the form of 8.1, after already having to do so for 8.0.

Microsoft's platforms are converging, but even with Windows Phone 8.1, they still won't be converged. They will, however, be an awful lot closer than they are right now. That probably deserves something more than a .1 version bump.