Methods and apparatus are provided for providing UE EPS capability information and receiving non-access stratum (NAS) security algorithm information for an interworking procedure in the 5GS network. In one novel aspect, the UE provides the UE EPS capability information in cleartext before the security mode procedure, and the NAS security algorithm information is included in a security mode command message during the security mode procedure. In one embodiment, the UE EPS capability information is an S1 mode indicator or the 5GMM capability information including the Si mode indicator. In another novel aspect, the network provides the NAS security algorithm information before interworking procedure from 5GS to LTE. In one embodiment, the network provides the NAS security algorithm information in the Registration Accept message. In another embodiment, the network provides the NAS security algorithm information in handover procedure from the 5GS to LTE.