Is Android officially supporting CTKD? From the BlueZ documentation:
Another improvement that LE SC brings is what’s called cross-transport key derivation. What this means is that when two dual-mode (supporting LE + BR/EDR) devices pair with each other, they only need to pair over either LE or BR/EDR to get the encryption keys for both transports in one go.
I haven't found any information in the official Android docs.