gRPC Motiviation and Design Principles - Google Project Page - Published 9/8/2015, states the gRPC is based on a Google internal project referenced as 'Stubby'. Used for microservice connectivity between a large number of services. Uses case extends for applicability to mobile, IOT, and Cloud use-cases due to release of SPDY, HTTP/2, and Quic. Stubby 're-worked' to take adavantage of standardization.
gRPC release Beta - Google Project Page - Published 8/26/2015, states gRPC Beta version released.
gRPC Project 1.0 - Google Project Page - Published 8/23/2016, states that gRPC Project is 1.0 and ready for production deployments for multiple languages.