A listing made today on Bluetooth SIG reveals Windows Phone 8.1 passing the certification. As can be seen in the above screenshot, the description clearly mentions “Mobile Phone operating system” and the design and design model number both bear “Windows Phone 8.1” name. The certified specification is Bluetooth 4.0 with low-energy, which is expected.
Windows Phone 8.1 may see a reveal during Build 2014. Some recent leaks have been seen, like notification center settings and separate volume control, while older leaks talk about Cortana, improved multitasking etc. Many sources have claimed similar timelines for Windows Phone 8.1 release.
Release to Manufacturers: March
Release to Developers: April
Release to Users: May