From documentation: Traffic Director delivers a GCP-managed Pilot along with additional capabilities such as global load balancing and centralized health check

From documentation: Traffic Director delivers a GCP-managed Pilot along with additional capabilities such as global load balancing and centralized health checking. However, note that Traffic Director cannot be configured using Istio APIs in this Beta release; you can use GCP APIs for configuration. Both Traffic Director and Pilot use open standard APIs (xDS v2) to communicate with service proxies.