The correct answer is Anthos. Anthos is GCP's modern application management platform that supports building, deploying, and operating applications across various environments, including on-premises and multiple clouds. It specifically includes features for managing service mesh, an infrastructure layer dedicated to controlling and monitoring communication between services in a microservices architecture.

• GKE (Google Kubernetes Engine) is a managed Kubernetes service for running containerized applications and can be part of Anthos, but it does not offer managed service mesh infrastructure on its own.
• Cloud Build is a CI/CD platform focused on building and deploying applications, not for service mesh infrastructure.
• Container refers to a technology for packaging and running applications, not a specific GCP service for managed service mesh.

Thus, Anthos is the correct choice for managed service mesh infrastructure in GCP.