You are building a cross-platform live dashboard that requires low-latency, bidirectional, real-time messaging over WebSocket. Clients must be able to join groups and the backend should scale without sticky sessions or custom WebSocket server management. What should you implement?

Azure Web PubSub service is the correct choice because it is a fully managed service specifically designed for real-time web applications using WebSockets. It handles WebSocket connections at scale, supports client groups for targeted messaging, and allows for a serverless architecture where you expose a negotiate endpoint for clients to get access tokens. Azure SignalR Service, while also real-time, is primarily for ASP.NET Core SignalR applications and SSE is not bidirectional. Azure Event Hubs is for event ingestion, not real-time bidirectional communication. Azure Relay Hybrid Connections are for connecting on-premises services to Azure, not for scalable public WebSocket endpoints. Operating custom WebSocket servers on VMs behind an Application Gateway introduces significant management overhead and doesn't offer the fully managed benefits of Web PubSub.