Accidentally high-revving your bike to 9000 RPM while it is in neutral is generally not harmful to the engine, especially if it only happened once. Most modern motorcycles are designed to handle higher RPMs and have built-in safety measures to protect the engine from damage. However, it's always a good idea to avoid unnecessarily high RPMs during the break-in period of a new motorcycle.
During the break-in period, manufacturers usually recommend keeping the engine speed within a certain range to allow the components to wear in properly and ensure optimal performance and longevity. It's important to follow the manufacturer's guidelines provided in the owner's manual for break-in procedures. These guidelines may include avoiding high RPMs, varying the engine speed, and gradually increasing the load on the engine over time.
While one accidental high-revving incident is unlikely to cause significant harm, it's still a good practice to be mindful of your bike's RPM and not excessively rev the engine, especially during the break-in period. If you have any concerns or notice any unusual behavior in your bike after the incident, it's recommended to have it inspected by a qualified motorcycle mechanic to ensure everything is functioning properly.