According to a report in Android Police, Copresence will use Wi-Fi Direct to transfer data and Bluetooth/ NFC for authentication as well as establishing a quick connection between the devices.
The current implementation of Android Beam is limited and needs the devices to feature NFC hardware and be in contact with each other to initiate a transfer. With Copresence, Google could remove the necessity of NFC hardware and use Bluetooth whenever the NFC is not present or something like that.
The exact details about the feature are unclear at this point but it looks like we could see the launch of Copresence soon. Till then, check out these Copresence related illustrations from Play Services teardown.
