What .NET 11 means for ASP.NET Core and Blazor

Strengthen the foundation - what you get just by upgrading

No code changes required. Kestrel cuts TLS handshake overhead for short-lived connections and sheds malformed requests more efficiently. Zstandard compression gives Brotli-level ratios at lower CPU cost. Security work hardens Kestrel, modernizes CSRF protection with fetch metadata headers, and adds auth token refresh for long-lived SignalR and Blazor Server connections. ASP.NET Core now emits OpenTelemetry tags natively, so every request is traced without extra instrumentation.

Invest in the modern stack - minimal APIs, SignalR, Blazor

Minimal APIs gain async validation and OpenAPI 3.2. Blazor gets the bulk of the work: static server-side rendering reaches parity with MVC, picking up temp data, output caching, and client-side validation that runs without interactivity. No websocket, no WebAssembly, just data validation attributes and localized messages. Async validation lands on EditContext via ValidateAsync.

On WebAssembly, the runtime moves from Mono to CoreCLR, previewing in 11 and stable in 12, so multithreading and 64-bit memory get built once. A new Web Worker template moves CPU-heavy work off the UI thread today. C# unions arrive across the stack.

Building Blazor apps that handle files? Our Blazor Excel export tutorial with IronXL covers creating and downloading XLSX from a Blazor Server app with no Office install, and our read-Excel tutorial covers loading worksheet data.

Simplify distributed apps - a production-grade Blazor story with Aspire

A new Blazor gateway service sits between browser and backend: it serves standalone WebAssembly apps, proxies API calls so there is no CORS to configure, flows service discovery config to the client, and feeds the Aspire dashboard. It replaces the old dev server with something you can run in production.

Enable agentic web apps - making web apps agentic

With the Microsoft Agent Framework, you can host agents inside ASP.NET Core apps, with built-in support for the OpenAI responses protocol, agent-to-agent orchestration, and AG-UI for real-time agent-to-UI interactions. Apps can act as an MCP server or client via the MCP C# SDK. Hosting an AG-UI endpoint is a single MapAgui call, and the AG-UI chat client implements IChatClient from Microsoft.Extensions.AI. Blazor AI components are in progress.

Co-pilot assisted development - teaching AI to write good .NET

Curated .NET skills, custom agents, CLI and MCP tools, and eval suites that measure whether any of it helps. The demo was direct: a Kanban board built without skills came out as one 300-line file; with the Blazor plugin and a plan-ui-change skill, it came out properly decomposed. Skills install on demand so they do not fill the context window.

The big picture

Stronger fundamentals on upgrade, new features concentrated in the modern stack, a production hosting story for Blazor WebAssembly via Aspire, AG-UI for the agentic web, and AI assistants that understand .NET. The November 2026 GA also marks the end of support for .NET 8 and .NET 9, worth factoring into migration plans. The previews are available now.

Want to build document and data features on top of the previews today? IronXL reads, writes, and exports Excel in Blazor Server with no Office dependency. See how it works in a Blazor app or try IronXL free for 30 days.