The features in the SDK for Windows Phone 8.1 have been leaked on Reddit ahead of the expected announcement at Build 2014. This adds to the line up of anticipated features that already included a personal digital assistant.

Although Microsoft would have liked to be able to unveil the next version of its Windows smartphone at  Build on April 2nd , when it was is expected that a public Developer Preview Program will be launched, many of its features have already been made public. 

The current release of the Windows Phone SDK has been made under a non-disclosure agreement to a limited number of key developers, but that hasn’t stopped the details of what’s in the SDK appearing on Reddit.

Assuming the details leaked are correct, it looks as though Microsoft plans to merge Windows Phone and Windows RT to a single platform thanks to support for ‘universal apps’, enabling apps in Windows Store and Windows Phone Store to run from shared HTML and Javascript.

The post on Reddit claims:

“universal apps is a template to build both WinStore and WinPhone apps from the same solution sharing code more easily”

The poster on Reddit also says that WP and WinRT will be categorized under Store Apps in Visual Studio, and that the main templates are universal apps that create both WP8 and WinRT projects, and that Windows Phone WP8 is now called WinPRT, according to the SDK documentation.

This video of the leaked SDK seems to show options including the ability to change the default messaging application for another, and added VPN support. Apps will be able to be suspended in the background in a similar way to Windows 8. The video opens with an ad that can be skipped after 3 seconds. 

While it is expected that the virtual assistant code-named ‘Cortana’ will be included, it is either missing or disabled in the SDK.

Cortana will be (assuming it appears) one of the main additions to Windows Phone 8.1. The personal digital assistant is named after a character in Microsoft's Halo game series, and was first seen in a Windows Phone 8.1 lost by a Microsoft employee last year. Cortana will be the default search option replacing the current Bing search, and will also act as a digital assistant along the lines of Apple’s Siri, though will look like an animated ball or emoticon.

In an interview on Bloomberg TV, Peter Lee, Head of Microsoft Researchtalks about the research Microsoft is doing on a personal digital assistant which is focussed on trying to answer questions and figure things out and to understand the intentions of people. 

The footage in the clip shows a male figure rather than an animated emoticon, with Lee saying the intention is to let users choose the avatar. This seems to be a more general piece of research, but it may well also be relevant to Cortona.