gRPC

A high-performance, open-source remote procedure call framework from Google that uses HTTP/2 for transport and Protocol Buffers (Protobuf) for binary serialization, offering lower latency, smaller message sizes, and bidirectional streaming compared to JSON-RPC over HTTP/1.1. In Solana infrastructure, gRPC is most prominent as the transport layer for Yellowstone, allowing clients to open long-lived streaming subscriptions with server-side filtering while consuming far less bandwidth than equivalent WebSocket subscriptions.