.NET 9 Preview 5

[jongalloway]

We are pleased to announce the release of .NET 9 Preview 5.

This release contains the following Libraries improvements:

• Enhanced AI capabilities with TensorPrimitives and Tensor<T>
• params offers better performance with Span overloads
• SearchValues can search for (multiple) substrings within a string
• foreach completed tasks with Task.WhenEach
• Prioritized unbounded channel
• OpenTelemetry activity linking is more flexible
• TypeDescriptor trimming support
• Type name parsing

For details on these new features and more see the Libraries Release Notes

You can find detailed release notes for additional features in .NET 9 Preview 5 below:

.NET Data & EF Core

• Enhanced database provider for Azure Cosmos DB for NoSQL
• Query translation improvements
• Full release notes

.NET MAUI

• Updated Blazor Hybrid Templates
• Android API 35 Beta 2 Support
• Android - LLVM Marshalled Methods
• Android - Trimming Enhancements
• Full release notes

ASP.NET Core

• Optimized static web asset delivery
• Improved Blazor Server reconnection experience
• Detect the current component render mode at runtime
• Simplified authentication state serialization for Blazor Web Apps
• New .NET MAUI Blazor Hybrid and Web solution template
• 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 5 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
• Containers

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.

[IrinaPykhova]

@jongalloway
after upgrading to Preview 5 I can't build my old code any more:

This is simple String.Split which now shows error
CS8652 The feature 'params collections' is currently in Preview and unsupported.

Is that some kind of breaking change?

[jaredpar]

This is an unintended consequence of the params collection feature in preview 5. The behavior for preferring new overloads is not tied to language version but the check for using params collection is. That means that you end up in this particular situation.. This was noticed when all of our bits come together in the sdk repo. After that discussed in C# LDM and fixed the behavior to avoid this type of problem. Should be fixed in .NET 9 Preview 6.

[julealgon]

@jaredpar can you elaborate what the fix will be? Is the "preferred overload" feature also going to be tied to the language version, or is the fix going to be something else?

[IrinaPykhova]

@IrinaPykhova do you have a sample project?

I assume this is targeting .NET 9... what is your LangVersion set to?

What happens if you set <LangVersion>preview</LangVersion> in your csproj?

you can check this sample: https://github.com/GrapeCity/ComponentOne-WPF-Samples/tree/master/NET_8/Scheduler/SchedulerExplorer
It targets .Net 8. If you change target to .Net 9, it won't build.
And it works if I set language version to preview.

[jaredpar]

@julealgon the logic to prefer the new overloads is also tied to language version.

[jspetit]

I had two persons on my team with the same issue. Updating VS 2022 to 17.10.* fixed the problem (they were 17.3 or 17.4).

[fabio-andre-rodrigues]

Hi all, does the preview 5 includes the openapi 3.1. generation tools?

[martincostello]

Do you mean built-in support for OpenAPI document generation? If so, yes.

[fabio-andre-rodrigues]

double yes

[SeanFarrow]

Are there any plans to make API diffs available for preview 5? They don't seem to be in the core repo.

[martincostello]

#9352

[richardaubin]

In reference to the Detect rendering location feature introduced here, is there a workaround for doing it in .net 8?

[danroth27]

Yes, there are some heuristics you can use with .NET 8. @rockfordlhotka wrote up a strategy he uses here: https://blog.lhotka.net/2024/03/30/Blazor-8-Render-Mode-Detection. The new RendererInfo formalizes support in the framework for .NET 9.

[richardaubin]

Yes, there are some heuristics you can use with .NET 8. @rockfordlhotka wrote up a strategy he uses here: https://blog.lhotka.net/2024/03/30/Blazor-8-Render-Mode-Detection. The new RendererInfo formalizes support in the framework for .NET 9.

Thanks, extacly what I was looking for.