Formal closure of a change management effort requiresapproval from the senior sponsor. This ensures the accountable executive validates that outcomes were achieved, ownership transferred, and sustainability measures are in place. The project manager approves project closure, while the change lead and training lead execute tasks but do not have the authority to formally close. Thus, the sponsor's approval is required to ensure accountability for benefits realization.
(Reference: ACMP Standard, Process Group 5 - Close; Activity: Seek formal sponsor approval for closure.)