Named after the AI character in Halo, Cortana is Microsoft's mobile digital assistant, designed to take on the likes of Siri and Google Now.
Sources attached to the project have leaked some images of Cortana in action to The Verge.
Sadly for Halo fans, the shots show a circular icon rather than the titular female avatar.as part of the next update and will replace Bing search.
Cortana will, of course, be voice activated, with the service designed to record and store information in a Notebook system. It can then use this information to learn more about user behaviour, refining the information it delivers by analysing previous requests. Cortana will also pre-emptively prepare searches and data based on location and habits.
Like Google Now, Cortana will be able to find travel information and other mentions in a user's email, then use that information to generate data about flight times and the like.
Microsoft is expected to reveal Cortana formally at the next Microsoft Build conference, with a developer preview of the 8.1 update likely to be issues at the same time.