If you want to make a breaking change, yeah - you need to version it. No question. It's fairly flexible in how much you can change without it being breaking, but it's not magic.

Beyond that it's arguably "versionless" because it does nothing to address the problem. Which is essentially fine, and is what most protocols do: you make a completely new API or change the endpoint (e.g. http path) to gradually make breaking changes (expose both, migrate callers whenever), because something like that is basically always an option.