Very similar to the approach AWS takes with ‘clientToken’ being an API parameter, not transport/protocol header, for operationz that need it. If clients dont specify a value the SDK will populate the idempotency token and handle retries etc transparently. The approach is that API/SDK/client semantics should be similar across services, but very few users care about actual transport or “on the wire” serialization.

Disclaimer: principal at AWS, but just general observations on this topic.