.NET 11 Arrives as .NET 8 and 9 Lose Support

Microsoft released .NET 11 on Nov. 10, 2026, pairing the C# 15 language with an MCP server template in the SDK and new tooling built for AI coding agents. The same day, .NET 8 and .NET 9 reached end of support, leaving .NET 10 and .NET 11 as the only supported versions.

Key takeaways

• .NET 11 is a Standard Term Support release, supported until Nov. 14, 2028, according to Microsoft's support policy page.
• C# 15 adds union types and closed hierarchies, and the SDK now ships a template for building Model Context Protocol (MCP) servers.
• .NET 8 and .NET 9 received final patches, 8.0.34 and 9.0.23, on Nov. 10 and no longer get security fixes.

What's new in .NET 11 and C# 15

C# 15 is the default language version for projects targeting .NET 11. Its headline feature, union types, lets a value be one of a declared set of types, with the compiler checking that switch expressions handle every case. Closed hierarchies limit direct inheritance to the declaring assembly so the compiler can check patterns over them.

Smaller additions include collection expression arguments, extension indexers and labeled break and continue. The .NET team's announcement says the SDK now runs a Native AOT command-line host and keeps the MSBuild server warm between commands by default to cut startup overhead.

Other changes: .NET MAUI makes CoreCLR its default runtime, and Entity Framework Core 11 adds experimental vector indexes and approximate vector search for SQL Server. Runtime Async, which moves async suspension into the runtime, remains a preview feature.

.NET 11 AI tools: MCP template, Agent Framework and .NET Skills

Developers can scaffold an MCP server with a single command, dotnet new mcpserver, built on the official MCP C# SDK. Microsoft points app builders to Microsoft.Extensions.AI for model access and Microsoft Agent Framework for agents and workflows.

The release also targets the coding agents themselves. .NET Skills is a GitHub repository of task-specific guidance from the .NET team that agents can load. The experimental .NET MAUI DevFlow toolkit exposes a running app's visual tree and screenshots so an agent can test the UI, and the .NET Upgrade canvas shows the progress of a GitHub Copilot upgrade session.

Some pieces are not finished. Microsoft says the new Blazor AI components package, which works with the Agent User Interaction Protocol (AG-UI), stays experimental and prerelease throughout .NET 11.

.NET 8 and .NET 9 end of support

Microsoft's .NET support policy lists Nov. 10, 2026, as the end of support for both .NET 8, an LTS release from 2023, and .NET 9. Apps built on them keep running but get no new security updates, InfoWorld reported in July.

.NET 10, the current LTS release, and .NET 11 are both supported until Nov. 14, 2028. Microsoft advises teams to update target frameworks, review breaking changes and test, noting: "Installing a new SDK alone doesn't retarget your app."

Context

Microsoft ships a major .NET version every November. .NET 11 went through three release candidates, on Sept. 8, Oct. 13 and Oct. 25, according to the support policy page. Microsoft credits more than 7,000 contributors and says NuGet hosts more than 589,000 unique packages with over 1.1 trillion downloads.

What's next

.NET Conf 2026 runs Nov. 10-13, with product team sessions on the first two days. The dotnetup toolchain manager is in public preview, and Microsoft says the AG-UI hosting integration is still prerelease.

FAQ

Should I pick .NET 10 or .NET 11? Both are supported until Nov. 14, 2028. Microsoft recommends .NET 11 for the latest features and .NET 10 if its LTS lifecycle fits better.

Will my .NET 8 app stop working? No. It keeps running, but it no longer receives security fixes or technical support from Microsoft.

References

• Announcing .NET 11 - .NET Blog — Microsoft (Nov. 10, 2026)
• .NET and .NET Core official support policy — Microsoft (updated Nov. 10, 2026)
• GitHub - dotnet/skills: Repository for skills to assist AI coding agents with .NET and C# — .NET team
• End of support looms for .NET 8 and .NET 9 — InfoWorld (July 1, 2026)