Which APIs on IOS XR are driven by YANG models?

All the mentioned APIs—NETCONF, RESTCONF, and gRPC—are indeed driven by YANG models in IOS XR environments. YANG, which stands for Yet Another Next Generation, is a data modeling language used to model configuration and state data for network devices.

NETCONF is an XML-based protocol that allows for the management of network devices, including configuration changes and state retrieval. It utilizes YANG models to define the structure and semantics of the data that can be manipulated through the protocol.

RESTCONF, on the other hand, is a more modern protocol that employs a RESTful approach to network management and works over HTTP/HTTPS. It leverages YANG data models for data representation and allows developers to access and manipulate network device configurations and states using standard REST techniques, making it more accessible for web applications.

gRPC is a high-performance remote procedure call framework that also supports YANG models. It allows for efficient communication between services and can utilize YANG for defining the data structures involved in the RPC calls.

As a result, since all three methods (NETCONF, RESTCONF, and gRPC) utilize YANG models to operate, the correct answer encompasses all the options listed.