Within service design, what is the key output handed over to service transition?

Measurement methods and metrics are components defined within the design process but are inputs and tools used during design, not the formal deliverable handed over to Service Transition.

The Service Design Package is the key output of the Service Design stage in ITIL. It contains all aspects of a service and its requirements through each stage of the lifecycle, including business requirements, service applicability, service contacts, design and topology, organizational readiness, and transition and operational plans - providing Service Transition with everything needed to build, test, and deploy the service.

Service portfolio design is an activity within Service Design concerned with the broader portfolio, not the specific package of documentation that gets transferred to the next lifecycle stage.

Process definitions are produced as part of design work but represent only one element of a larger deliverable; they are not the key output handed to Service Transition as a whole.