Is the wire protocol exclusive to server<->server communication, or is it used for server<->client communication? If the latter applies, then alternative client

Is the wire protocol exclusive to server<->server communication, or is it used for server<->client communication? If the latter applies, then alternative clients would not be any more or less free of restrictions than alternative servers would be. Note that I'm not addressing whether the wire protocol's license affects server/client implementations — that's being discussed in a different top-level thread — I'm only addressing whether a difference could exist between server/client. (I am not your lawyer, please do not treat social media comments as legal advice, etc.)