Microsoft is starting to distribute Windows Phone 8.1 to existing Lumia devices this week. The Lumia Cyan update provides the full Windows Phone 8.1 software, alongside some tweaks and customizations specifically for Lumia handsets. Windows Phone 8.1 includes a personal digital assistant in the form of Cortana, a number of new customization features for Live Tile layouts, a new Word Flow keyboard, a notification center, and much more.

The Lumia Cyan part of the update includes a motion data app that collects data for fitness apps like Bing Health & Fitness or Active Fitness. It also includes Bluetooth 4.0 low-energy support, mircast options, and improvements to the camera algorithms for the Lumia Icon, Lumia 1520, and Lumia 930 for improved low-light performance, better color reproduction, and auto-focus improvements. Cyan also adds a new living images feature that briefly records the couple of seconds before a photo is taken to animate images in the photo gallery. Microsoft says the Lumia Cyan update and Windows Phone 8.1 are rolling out around the world today, and will be available for all Windows Phone 8 Lumia devices over the coming weeks. If you want to check individual carrier availability then Microsoft has an update tracker right here.