I believe it's 4.0. Here's is the hardware result. It runs at USB version 1.0 though so I can't imagine it's fast. If there were a way to turn this one off I'd get a dongle adapter if you need higher speed but there isn't.
Description: Realtek Semiconductor Corp. Bluetooth driver update released in June 2017
Supported products: Windows 10 Creators Update and Later Servicing Drivers , Windows 10 S and Later Servicing Drivers
Supported languages: Arabic , Bulgarian , Chinese - Hong Kong SAR , Chinese (Simplified) , Chinese (Traditional) , Croatian , Czech , Danish , Dutch , English , Estonian , Finnish , French , German , Greek , Hebrew , Hungarian , Italian , Japanese , Japanese NEC , Korean , Latvian , Lithuanian , Norwegian , Polish , Portuguese (Brazil) , Portuguese (Portugal) , Romanian , Russian , Serbian (Latin) , Slovak , Slovenian , Spanish , Swedish , Thai , Turkish , Ukrainian
Company: ASUSTeK Computer Inc.
Driver Manufacturer: Realtek Semiconductor Corp.
Driver Class: Other Hardware
Driver Model: Realtek Bluetooth 4.0 Adapter
Driver Provider: Realtek Semiconductor Corp.
Version Date: 6/12/2017
Support Url: n/a