Announcing .NET Core 3.0 Preview 7

Rich Lander [MSFT]

Today, we are announcing .NET Core 3.0 Preview 7. We’ve transitioned from creating new features to polishing the release. Expect a singular focus on quality for the remaining preview releases.

Download .NET Core 3.0 Preview 7 right now on Windows, macOS and Linux.

ASP.NET Core and EF Core are also releasing updates today.

Visual Studio users need Visual Studio 2019 16.3 Preview 1 to use .NET Core 3.0 Preview 7.

The Microsoft .NET Site has been updated to .NET Core 3.0 Preview 7 (see the version displayed in the website footer). It’s been running successfully on Preview 7 for over two weeks, on Azure WebApps (as a self-contained app). We will likely move the site to Preview 8 builds in a couple of weeks.

ICYMI, check out the improvements we released in .NET Core 3.0 Preview 6 and the June Update on WPF, both from last month.

Go Live

NET Core 3.0 Preview 7 is supported by Microsoft and can be used in production. We strongly recommend that you test your app running on Preview 7 before deploying Preview 7 into production. If you find an issue with .NET Core 3.0, please file a GitHub issue and/or contact Microsoft support.

We intend to make very few changes after Preview 7 for most APIs. Notable exceptions are: WPF, Windows Forms, Blazor and Entity Framework. Any breaking changes after Preview 7 will be documented.

We are working to ensure a high degree of compatibility with .NET Core 1.x and 2.x apps, making it straightforward to upgrade existing apps to .NET Core 3.0.

.NET Core SDK Size Improvements

The .NET Core SDK is significantly smaller with .NET Core 3.0. The primary reason is that we changed the way we construct the SDK, by moving to purpose-built “packs” of various kinds (reference assemblies, frameworks, templates). In previous versions (including .NET Core 2.2), we constructed the SDK from NuGet packages, which included many artifacts that were not required and wasted a lot of space.

You can see how we calculated these file sizes in the .NET Core 3.0 SDK Size Improvements gist. Detailed instructions are provided so that you can run the same tests in your own environment.

.NET Core 3.0 SDK Size (size change in brackets)

Operating System Installer Size (change) On-disk Size (change)
Windows 164MB (-440KB; 0%) 441MB (-968MB; -68.7%)
Linux 115MB (-55MB; -32%) 332MB (-1068MB; -76.2%)
macOS 118MB (-51MB; -30%) 337MB (-1063MB; -75.9%)

The size improvements for Linux and macOS are dramatic. The improvement for Windows is smaller because we have added WPF and Windows Forms as part of .NET Core 3.0. It’s amazing that we added WPF and Windows Forms in 3.0 and the installer is still (a little bit) smaller.

You can see the same benefit with .NET Core SDK Docker images (here, limited to x64 Debian and Alpine).

Distro 2.2 Compressed Size 3.0 Compressed Size
Debian 598MB 264MB
Alpine 493MB 148MB


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.

We recommend that you start planning to adopt .NET Core 3.0. This recommendation is stronger if you are using containers. The 3.0 improvements for containers are critical for anyone using docker resource limits directly or via an orchestrator.

If you install daily builds, please read an important PSA on .NET Core master branches.


Discussion is closed. Login to edit/delete existing comments.

  • Byron Adams 0

    Is there a documentation of ‘breaking changes’. The api changes do not seem to help.  My app had 0 errors/warnings. Now I get a ton.  I even removed the obj folders, did a restore and rebuild.Here are some:  <NullableContextOptions>enable</NullableContextOptions> in the project file, does it still work. I get CS8627 A nullable type parameter… errorsCS1069 Icon could not be in System.DrawingCS0234 The type or namespace name ‘Forms’ does not exist in the namespace ‘System.Windows’…

    • Raja Venkatesh 0

      This happened to me too. I had updated VS2019 from 16.1.x to 16.2.0.  That was the issue.
      In VS2019 go to Tools\Options\Environment\Preview Features and select “Use previews of the .NET core SDK (requires restart)” check box.  I had done this in the previous minor version of VS2019 but the new version resets it back.  After checking this option on, the project uses .NET Core 3.0 Preview 7 and compiles fine without any changes in the code.  My code targets WPF apps built using VB.NET.

      • Byron Adams 0

        Just tried again with 16.2 and no go.  At work I have another machine with 16.3, it does not work either.

      • Alexey Leonovich 0

        I had the same issue. Was forced to check “Use previews of the .NET core SDK (requires restart)” checkbox again.

    • Phillip CarterMicrosoft employee 0

      <NullableContextOptions> is now <Nullable>. This is one of the changes we made from preview to preview for the C# 8 preview chain.

    • Byron Adams 0

      I changed <NullableContextOptions> is now <Nullable>, but no change in compiling and no fix suggestions like before.I was able to solve the problem: CS1069: The type name ‘Icon’ could not be found in the namespace ‘System.Drawing’. This type has been forwarded to assembly ‘System.Drawing.Common, Version=, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51’ Consider adding a reference to that assembly.After not finding an Add Refenence->Assemblies item. I went to Nuget, but the version is System.Drawing.Common 4.6.0-preview7.19362.9.Now I tried the same with this error: CS0234: The type or namespace name ‘Forms’ does not exist in the namespace ‘System.Windows’ (are you missing an assembly reference?)I thought having <Project Sdk=”Microsoft.NET.Sdk.WindowsDesktop”> and <UseWPF>true</UseWPF> would fix this problem like before.  Went to Nuget and could not find System.Windows.Forms.Should would help if there were some documentation on migrating.

  • Ian Qvist 0

    Windows Forms is part of the installer on Linux and Mac too?

    • Gavin Williams 0

      No, that’s why they are smaller.

  • Afshin Z 0

    Any news on the GPIO and IoT stuff? There are tons of boards out there, what boards are supported?
    One more question: Can we use Gamepad/Controllers with .NET Core 3.0? I know UWP supports Xbox One controller, what about .NET Core 3.0?

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