The Google Cloud client libraries are open-source; I don't really see the difference.
I should also point out: often, with this type of project (in-the-open development of a client for a paid service) the client comes with some sort of stub emulator for the service. FOSS developers can test their changes against the emulator, and then submit PRs, which then get run by CI against the real service.
I should also point out: often, with this type of project (in-the-open development of a client for a paid service) the client comes with some sort of stub emulator for the service. FOSS developers can test their changes against the emulator, and then submit PRs, which then get run by CI against the real service.