Announcing .NET Core 3.0 Preview 7



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 SystemInstaller Size (change)On-disk Size (change)
Windows164MB (-440KB; 0%)441MB (-968MB; -68.7%)
Linux115MB (-55MB; -32%)332MB (-1068MB; -76.2%)
macOS118MB (-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).

Distro2.2 Compressed Size3.0 Compressed Size


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.

Richard Lander

Program Manager, .NET Team

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Max Mustermueller 2019-07-23 12:06:45
We can use and build .NET Core WPF and Winforms app even when a third party control dependency targets .NET Framework. But now as we have a "go live" build of .NET Core I wonder how it works with self contained publishing. Would it run by itself or does the .NET Core 3 application still requires .NET Framework installed only because a third party dependency has target it. That's currently my biggest blocker, not many companies provide .NET Core binaries of their control suites yet.
Ma, Chuanshan 2019-07-23 18:26:17
Should it be RC instead of preview?
Алексей Леонович 2019-07-24 01:03:19
"We will likely move the site to Preview 8 builds in a couple of weeks." - it will be in August 2019.. But .NET Core RC was promised in July 2019 - what is current schedule? And BTW: Any plans for making possible to do PublishReadyToRun and PublishTrimmed in Publish window? I mean, we do not use the command line and get inside Visual Studio without editing project file.
Ian Marteens 2019-07-24 01:33:45
No Windows Forms Designer yet?
Max Mustemann 2019-07-24 02:56:12
Any details on why .NET Core 3.0 Preview 7 requires VS 16.3 Preview? When .NET Core 3.0 Preview 7 is "Go Live" and can be used for production, I still would need to use a preview version of Visual Studio that is *not* supported for writing production code. However, I tested the .NET Core 3.0 Preview 7 SDK with Visual Studio 16.2 Preview 4 and did not notice any problem, so I'm wondering why that 16.3 requirement is.
Yahor Sinkevich
Yahor Sinkevich 2019-07-24 12:16:35
Please provide ApiDiff from the 2.2
Behnam Emamian
Behnam Emamian 2019-07-24 19:19:06
It is good to document the changes: 1)Json librarySystem.Text.Json.Serialization => System.Text.Json 2)JsonSerializer.Parse => JsonSerializer.Deserialize 3) JsonSerializer.ToString => JsonSerializer.Serialize
Tony Henrique 2019-07-25 07:40:00
Mark Adamson
Mark Adamson 2019-07-25 09:55:42
It sounds like we won't be able to build WPF apps on Linux build servers due to the SDK bundle not including the Desktop SDK. Is that correct? The rest sounds great :)
Andrew Osman
Andrew Osman 2019-07-28 14:21:25
Can you please give any clarity around support for C++ / CLI, even if its only for Windows. Thanks! 
Byron Adams 2019-07-28 19:12:38
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'...
Cinema Choob
Cinema Choob 2019-07-30 02:27:21
Ian Qvist 2019-08-03 16:43:00
Windows Forms is part of the installer on Linux and Mac too?
Afshin Z 2019-08-04 11:30:15
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? Thanks,