The documents related to the filing show that Windows Phone 8.1 has been certified against version 4.0 of the Bluetooth specification and is Bluetooth SMART ready (i.e. support for Bluetooth Low Energy).
In the filing Windows Phone 8.1 is described:
The first major update to Windows Phone 8 expands the range of hardware options while simultaneously opening up the developer experience that enables even more fantastic apps. From the Bluetooth perspective, Windows Phone 8.1 adds Low Energy APIs that connect to a wider world of personal gadgets.
Windows Phone 8 already has hardware (driver) support for Bluetooth Low Energy (added in GDR2 software update), but there are currently no public APIs to allow third party developer use (private APIs d currently exist). The certification confirms our previous speculation that the public Bluetooth Low Energy APIs will be added in Windows Phone 8.1.
The certification documents also includes information on what profiles will be supported by Windows Phone 8.1. A notable absence in the HID profile, which means the platform still will not support the use of Bluetooth enabled keyboards and mice.
In the certification submission document two dates are given. The first is for date which the EPL (End Product Listing) will be published on the Bluetoth website (1st March 2014) and the second is for the date which the product is available for purchase (1st April 2014). The second of these provides strong supporting evidence for the formal announcement of Windows Phone 8.1 at Microsoft's Build 2014 conference, which takes place at the beginning of April.