Which stage of the service lifecycle includes the scope of service retirement and transfer of services between service providers?

Service Transition handles the actual execution of transitions such as deployments and decommissions, but defining the scope and design approach for retirement or provider transfer is a Service Design responsibility.

Service Level Management is a process within Service Design, not a lifecycle stage, and it does not define the scope of service retirement or inter-provider transfers.

Service Operation manages day-to-day delivery of live services and does not define the scope of retirement or the transfer of services between providers.

The ITIL Service Design publication defines its scope as covering the design of new or changed services, service retirement, and the transfer of services to or from external service providers. These concerns are addressed at the design stage so that plans, contracts, and supporting architectures for ending or transferring services are built in from the outset rather than added reactively.