Hence, the qualification of stable API. You can mark fields as unused and fields as optional (recently): https://stackoverflow.com/a/62566052 https://stackover

Hence, the qualification of stable API. You can mark fields as unused and fields as optional (recently): https://stackoverflow.com/a/62566052 https://stackoverflow.com/a/62566052 When your API changes that dramatically, you should use a new message definition on the client and server and deprecate the old RPC.