Server-Sent Events in ASP.NET Core and .NET 10

ASP.NET Core 10 introduces native Server-Sent Events (SSE) support as a lightweight alternative to SignalR for one-way real-time updates. SSE uses standard HTTP with the text/event-stream content type, requires no client libraries, and supports automatic browser reconnection. The new Results.ServerSentEvents API works with IAsyncEnumerable to stream data, handles missed events via Last-Event-ID headers, and integrates seamlessly with existing authentication and authorization. SSE is ideal for dashboards, notifications, and progress bars where bidirectional communication isn't needed, while SignalR remains better for complex two-way scenarios.