Machine identity security has evolved significantly with the rise of AI, transforming machine identities from static service accounts into autonomous agents that make real-time decisions and interact dynamically with other services. Traditional security models are inadequate for managing the risks associated with these advanced machine identities, which now require a focus on understanding their actions, interactions, and trust propagation within systems. Relationship-Based Access Control (ReBAC) offers a more suitable framework by modeling systems as graphs of relationships, enabling better management of permissions and delegation. This approach ensures machine identities are held accountable and auditable, allowing for dynamic delegation and preventing unauthorized access. Implementing practices such as risk scoring, time-to-live on trust, and explicit relationship modeling is crucial in securing AI-driven systems, ensuring they remain safe, predictable, and accountable amidst growing complexity.