The refreshed apps are available to only those running developer preview version of Windows Phone 8.1 or those who have purchased new devices running Windows Phone 8.1.
We are releasing a broad set of updates to the Bing Apps which are available for download and will now ship standard on new Windows Phone devices. The app updates are available only to users on Windows Phone 8.1 which is currently in developer preview. It will be available to existing users running compatible hardware and on the next wave of Windows Phone devices in the coming months