All Publishers returned from the API are cold, meaning that no I/O happens until they are subscribed to and the subscription makes a request. So just creating a Publisher won’t cause any network IO. It’s not until Subscription.request() is called that the driver executes the operation.

This is incorrect as its the subscription that may trigger i/o see: Hot Versus Cold with cold publishers nothing happens before you subscribe - regardless of the initial demand. So some IO may occur on subscribe, determining sessions / creating cursors.