gogoprotobuf is a fork of golang/protobuf with extra code generation features. With this new release comes a new internal library version. This means any newly generated *pb.go files generated with the v1.3.0 library will not be compatible with the old library version (v1.2.1). However, current *pb.go files (generated with v1.2.1) should still work with the new library. Please make sure you manage your dependencies correctly when upgrading your project.