.NET 9 Preview 4

[jamesmontemagno]

We are pleased to announce the release of .NET 9 Preview 4. This release contains the following Libraries & Runtime improvements:

• UnsafeAccessorAttribute supports generic parameters
• Feature switches with trimming support
• Tokenizer library enhancements
• OpenTelemetry: Make activity linking more flexible
• PDB support for System.Reflection.Emit.PersistedAssemblyBuilder

For details on these new features and more see the Libraries release notes and Runtime release notes

Discuss this release with the .NET team on GitHub Discussions.

You can find detailed release notes for additional features in .NET 9 Preview 4 below:

.NET Data & EF Core

• Enhanced database provider for Azure Cosmos DB for NoSQL
• GroupBy complex types
• Read-only primitive collections
• Full release notes

.NET MAUI

• New Input Keyboards
• Android 15 Beta 1 Support
• NativeAOT improvements for iOS & Mac Catalyst
• Full release notes

Discuss this release with the .NET MAUI team on GitHub Discussions

ASP.NET Core

• Built-in support for OpenAPI document generation
• Introducing HybridCache
• Developer exception page improvements
• Added OverscanCount parameter to QuickGrid
• Add static SSR pages to a globally-interactive Blazor Web app
• Avoid 503's during app recycle in IIS
• Full release notes

Discuss this release with the ASP.NET Core team on GitHub Discussions.

WPF

• Theming improvements – Support for Windows 11 theming for WPF apps
• Hyphen based ligature support
• Full release notes

Get started

To get started with .NET 9, install the .NET 9 SDK.

If you're on Windows using Visual Studio, we recommend installing the latest Visual Studio 2022 preview, or get started with Visual Studio Code and the C# Dev Kit extension.

You can find .NET 9 Preview 4 Installer & Binaries on GitHub.

Team Announcements & Discussions

Discuss this release with the product teams on GitHub through the announcements for this release.

• .NET MAUI
• ASP.NET Core
• Libraries & Runtime
• Source-build

Stay up-to-date with .NET 9

You can stay up-to-date with all the features of .NET 9 with:

• What's new in .NET 9
• What's new in ASP.NET Core
• What's new in .NET MAUI
• What's new in EF Core
• Breaking Changes in .NET 9
• .NET 9 Releases

For .NET 9 previews we are utilizing GitHub Discussions to make announcements. For more information read our discussion.

Stay up to date by subscribing to the RSS feed for all release announcements.

Engage with the product teams by commenting below as you try out these new features or have questions.

[hez2010]

The link to MAUI release notes is incorrect. It should be https://github.com/dotnet/core/blob/main/release-notes/9.0/preview/preview4/dotnetmaui.md

[jamesmontemagno]

This is updated

[jeromelaban]

Congrats on the release!

One thing dotnet workload install maui fails with:

Workload installation failed: One or more errors occurred. (Version 17.0.8523 of package microsoft.ios.sdk.net8.0_17.0.msi.x64 is not found in NuGet feeds https://api.nuget.org/v3/index.json.)

Should we be waiting for some package publication later today? I know @rolfbjarne had to do something for preview 3, maybe it needs to be done the same for preview 4?

[rolfbjarne]

Hm yeah, looks like some packages are missing. Looking into it now.

[rolfbjarne]

Should be all published now.

[jeromelaban]

It's working, thanks for the quick update!

[mhedden94]

Glad to see support for WPF and Windows 11 styling. However, even after installing the latest .NET 9 preview 4 SDK and preview version of Visual Studio 2022, building a WPF app on Windows 11 still shows the old control design. I don’t see any option to enable or force the new design elements.

[mhedden94]

Worked perfectly, thank you!

[jamesmontemagno]

Updated the docs with this :)

[kumoh2]

nice

[arknu]

@jamesmontemagno Is this intended to be needed for the final release? If so, seems kind of silly. Who would not want the new styles by default? You could have a switch the other way round, if you need the old styles for compatibility.

[jamesmontemagno]

I would inquire on the WPF repo: https://github.com/dotnet/wpf

[PaskalSunari]

Congrats for the release

[IrinaPykhova]

Congratulations with release. @jamesmontemagno I have some questions about WPF Fluent theme:

• if you use it in application, what would happen if this application runs on Windows 10?
• what are your plans about target frameworks? Would it be .Net 9 only, or we will be able to use it in earlier versions? What about .Net framework?
• do you plan something for control authoring? For old themes, you could include theme-specific resources into your library as described here: https://learn.microsoft.com/en-us/dotnet/desktop/wpf/controls/control-authoring-overview?view=netframeworkdesktop-4.8#defining-resources-at-the-theme-level. Would it be possible to do the same for Fluent theme? Or maybe you will obslete this mechanism entirely?

[IrinaPykhova]

@jamesmontemagno do you have any insights about my questions?

[jamesmontemagno]

Best thing to do would be to ask on the WPF repo: https://github.com/dotnet/wpf

[valco1994]

I can't compile .NET 9 application on macOS Big Sur x64 with .NET 9 preview 4 due to Symbol not found: __ZNSt3__113basic_filebufIcNS_11char_traitsIcEEE4openEPKcj in libhostfxr.dylib.

Is it intentional? Does .NET 9 require macOS 12+ now?

[jamesmontemagno]

@richlander ?

[richlander]

@elinor-fung ?

[fraluderin]

Congratulations on this release and thanks to all the contributors for this great result... finally WPF gets the attention it deserves! I can't believe it is finally getting theme updates. Any news on extending nullable context annotations on WPF library?