Apparatuses, systems, and methods for a user equipment device (UE) to establish a connection with a core network through a base station configured with mixed core network deployment, wherein the base station is communicatively coupled to each of a LTE core network (CN) such as an evolved packet core (EPC) and a 5G CN. The UE determines a preference for establishing a connection with one of the EPC or the 5G CN based on one or more of a device type of the UE, an active data flow running on the UE, an availability of network slices or packet data unit (PDU) sessions through each core network, or historical network performance of a particular CN. The UE transmits a message to the base station indicating the determined preference. The UE subsequently receives a response from the base station establishing a connection with the indicated preferred core network.