Which stage is NOT part of the continual improvement model in ITIL 4?

The continual improvement model in ITIL 4 is designed to enable organizations to identify opportunities for improvement and implement changes that enhance their services and processes. This model consists of several key stages that guide teams in assessing their current state, defining objectives, and maintaining progress over time.

The stage "What is the cost of services?" does not fit within the continual improvement model's structure. This stage focuses on the financial aspect of service delivery rather than on the assessment or implementation aspects of continual improvement. The model emphasizes understanding the current status, establishing a vision for future improvement, and determining how to sustain improvements over time, rather than strictly evaluating the costs associated with services.

In contrast, the stages "Where are we now?" and "What is the vision?" pertain directly to assessing the current state of processes or services and setting goals for improvement. "How do we keep the momentum going?" emphasizes the importance of sustaining improvements to ensure that the initiatives lead to long-term benefits. Therefore, while assessing costs is an important function in service management, it is not classified as a stage within the continual improvement model itself.