Announcing .NET Core 3.0 Preview 9



Today, we’re announcing .NET Core 3.0 Preview 9. Just like with Preview 8, we’ve focused on polishing .NET Core 3.0 for a final release and aren’t adding new features. If these final builds seem less exciting than earlier previews, that’s by design.

Download .NET Core 3.0 Preview 9 right now on Windows, macOS, and Linux.

ASP.NET Core, EF Core and Visual Studio are also releasing updates today.


.NET Core 3.0 is launching at .NET Conf

Tune in for .NET Conf, September 23-25th. We will launch .NET Core 3.0 during .NET Conf. Yes, that means that Preview 9 is the last preview, and .NET Core 3.0 will be released in its final version later this month. We have a lot of great speakers and content prepared for .NET Conf this year. It’s one of the big .NET developer events each year, and you cannot beat the price. It’s free and streaming online.

Visual Studio Support

.NET Core 3.0 is supported with Visual Studio 2019 16.3 Preview 3 and Visual Studio for Mac 8.3, which were also released today. Please upgrade to it for the best (and supported) experience with .NET Core 3.0 Preview 9. See Visual Studio 2019 16.3 release notes for more information.

We know that some folks have been successful using .NET Core 3.0 builds with Visual Studio 2019 16.2 and wonder why 16.3 is required. The short answer is that we only test .NET Core 3.0 with Visual Studio 2019 16.3 and have made many improvements and key fixes that are only in 16.3. The same model applies to Visual Studio for Mac 8.3.

The C# Extension for Visual Studio Code is always updated to support new .NET Core versions. Make sure you have the latest version of the C# extension installed.

Go Live

NET Core 3.0 Preview 9 is supported by Microsoft and can be used in production. We strongly recommend that you test your app running on Preview 9 before deploying into production. If you find an issue with .NET Core 3.0, please file a GitHub issue and/or contact Microsoft support.

The Microsoft .NET Site has been updated to .NET Core 3.0 Preview 9 (see the .NET Core runtime version in the footer text). It’s been running great on previews, starting with Preview 7, on Azure WebApps (as a self-contained app). Check out the Microsoft .NET site and see for yourself how it performs on Preview 9.


The .NET Core 3.0 release is coming close to completion, and the team is solely focused on stability and reliability now that we’re no longer building new features. Please tell us about any issues you find, ideally as quickly as possible. We want to get as many fixes in as possible before we ship the final 3.0 release.

If you missed earlier (more exciting) posts about .NET Core 3.0, check out the improvements that were part of .NET Core 3.0 Preview 6 (last preview with new features) and earlier releases.

If you install daily builds, read an important announcement about .NET Core master branches.

Richard Lander

Program Manager, .NET Team

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    • Olia Gavrysh
      Olia Gavrysh

      We will release a first preview version of the WinForms designer around the .NET Core 3.0 GA. It’s still very early days for the designer. This version willl support only some common controls and basic operations just to give you a sneak peek on the progress we’ve done so far. After that we will be releasing new preview versions on a regular cadence.

  • Avatar
    Max Mustermueller

    When will .NET Core 3 ship with a Windows update? That would be great to know when our customers should have it by default (ignore self contained publish in this case) just like .NET Framework.

  • Avatar
    Dave Nay

    I thought .NET Core 3.0 was supposed to cleanup old installed versions proactively? I still have dozens of versions installed (including previews 6, 7, and 8) after installing P9.

      • Avatar
        Livar Cunha

        .NET Core starting with SDK 3.1.100 will upgrade itself. Meaning, if you had 3.1.100 and are now adding 3.1.101, then 3.1.100 will be replaced by the newer one.
        It won’t proactively remove older versions like 2.1.x, 2.2.x, etc.

  • Avatar
    Alexey Leonovich

    1) Does this preview support building C++/CLI projects for Windows?
    2) Does x64 .NET Core SDK installer already includes x86 or I need to install both on x64 machine? The same question for .NET Core runtimes.
    3) Is .Net Core 3 supposed to be used in offline (disconnected) scenarios? Because for now it’s impossible to compile template Windows Forms App (.NET Core) with Visual Studio 2019 Professional 16.3 preview 3 and .NET Core 3-preview9 if PC cannot reach –

    • Avatar
      Livar Cunha

      1) Coming in .NET Core 3.1 and VS 16.4
      2) VS will install the runtime for both x86 and x64 if you are on a x64 machine and installing x64 VS. It won’t install both SDKs because that’s not really necessary. You can target x86 from a x64 SDK.
      3) That should work. That VS feedback item is for preview3. What error exactly are you getting with preview9? You should see a restore failure if there is any package missing, which should not be the case for a vanilla winforms project targeting net core.

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    VB User1

    Why are these features removed in preview 9? — Microsoft.VisualBasic.ApplicationServices, Microsoft.VisualBasic.Devices, Microsoft.VisualBasic.MyServices. — I’m worried because I frequently use Microsoft.VisualBasic with .NET Framework.

    • Avatar
      Kathleen Dollard

      These classes have dependendies on WinForms.
      In .NET Core, we are splitting the Visual Basic runtime into a portion in CoreFx and a portion that depends on WinForms. As we’ve previously announced, WinForms support will not be in .NET Core 3.0. 
      We initially thought we could split these classes and included portions of these classes in CoreFx and earlier previews contained these classes. We realized this was a terrible idea – it relied heavily on reflection and would give runtime errors when WinForms was not availble. Thus, we removed all but one of the classes that depends on WinForms. We left Interaction because it contains IIf. 

  • Avatar
    Bob Howell

    Seems that while some of the wonks were resolved in the Wpf designer, seems now data binding is fubar. “Bind to Data Source” is grayed out in the properties window context menu. You cannot select a data context, like a view model. Ugh guys should this not have been obvious? You can stil type it directly into the XAML but I am a visual person. I like the designers.

  • Avatar
    VB User1

    P/Invoke StgOpenStorage(OLE32.DLL) is crash.
    There is no problem with .NET Framework, but it crashes with .NET Core Preview 9.
    <DllImport(“OLE32.DLL”, CharSet:=CharSet.Auto)>Public Shared Function StgOpenStorage(<MarshalAs(UnmanagedType.LPWStr)>ByVal pwcsName As String,ByVal pstgPriority As IStorage,ByVal grfMode As STGM,<MarshalAs(UnmanagedType.LPArray)>ByVal snbExclude() As String,ByVal reserved As Integer,<Out()>ByRef ppstgOpen As IStorage) As HRESULTEnd Function

  • Massimo Signoretto
    Massimo Signoretto

    HI RichardI am following the Blazor platform with great interest, I am having problems with the use of the areas in the mapping of the images, I explain myself better if I insert in NoHref to prevent the post from the page, the onclick does not work, you would call me a Correct way to use the images with mapped areas Thanks anyway

  • Avatar
    Phil Harris

    I’m not following something…  that .Net Core 3.0 Preview 9 is supported for production, but requires VS 2019 16.3 Preview which states that it is not licensed for production release. Can you clear up my confusion?  Not that I have anything to imminently release.  Just want to understand.

    • Avatar
      Daniel Eldström

      If you want to develop something using .net core 3.0 preview 9 using full Visual studio you need to use 2019 16.3 preview afaik but you can, as i have use VS Code or any other text/code-editor out there to create a dotnet core app using .net core 3.0 preview 9 and have the golive license since you then only use the dotnetcore libs and sdk to compile and publish the app. You could most likely develop it and test using VS 2019 16.3 also but doing the actual last build and deploy using the dotnet build/publish tools.

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