Microsoft's promised delivery of its Windows Phone 8 software development kit (SDK) some time "this summer" has now shifted to "later this year."

In a September 5 post on the "Windows Phone Developer" blog, Microsoft officials acknowledged the new, later timing. The new estimated delivery time for the full SDK is at the same time as when Microsoft launches Windows Phone 8. The Windows Phone 8 launch date is October 29 , according to my sources. (Microsoft still hasn't officially confirmed the October 29 date, but I'm feeling pretty darn confident of it, for what it's worth.)

Next week, on September 12, Microsoft will "share detailed instructions on how current Windows Phone developers with published apps can apply to obtain the near-final Windows Phone 8 SDK seemingly in the next couple of weeks. However, the number of developers who will get the SDK will be "limited," officials warned. The full publicly-released Windows Phone 8 SDK isn't due until the Windows Phone 8 launch.

Microsoft has been making private builds of its Windows Phone 8 SDK available to a small number of developers outside the company since earlier this year. An early version of the SDK leaked earlier this summer.

Developers are clamoring for the new SDK because Microsoft has made major, deep-level changes to the Windows Phone operating system between the current 7.x version and the coming Windows Phone 8 OS release. Microsoft is now using the Windows 8 core inside the Windows Phone 8 operating system. The coming Windows Phone 8 operating system also includes a number of brand-new featues, like multicore support, NFC support, encryption and more of which many developers want to take advantage.

Microsoft also is switching up how different developer tools and technologies will work with Windows Phone 8 -- something else that has developers interested in getting their hands on the SDK.

That said, Microsoft is guaranteeing that Windows Phone 7.x apps will run on Windows Phone 8.

Back in June, Microsoft officials disclosed many of the coming Windows Phone 8 operating system features that will be core to Microsoft's next-generation smartphone operating system. On September 5, during a Microsoft-Nokia Windows Phone 8 event in New York , Microsoft execs added a couple of previously officially undisclosed features to that list, including new "lenses" that look somewhat like Instagram filters, the ability to do screenshots on Windows Phones, pinch zoom support in the camera.

Microsoft officials said they wouldn't be disclosing the full set of Windows Phone 8 OS features until a later, unspecified date.