Warning emitted for .NET Standard 1.x targets
A warning is now emitted when a project that targets netstandard1.x is built with the .NET 9+ SDK.
Previous behavior
Previously, you could build a project that targeted .NET Standard 1.0 - .NET Standard 1.6 without any build warnings.
New behavior
Starting in .NET 9, if you build a project that targets .NET Standard 1.0 - .NET Standard 1.6, the following warning is emitted:
warning NETSDK1215: Targeting .NET Standard prior to 2.0 is no longer recommended. See https://aka.ms/dotnet/dotnet-standard-guidance for more details.
Version introduced
.NET 9 Preview 6
Type of breaking change
This change can affect source compatibility.
Reason for change
The build warning was introduced to encourage customers to target .NET Standard 2.0 or .NET 6+. If you target .NET Standard 1.x, you're limiting yourself to a subset of .NET Framework 4.5, which is over 10 years old. A lot of innovation has happened since then that you're missing out on. In addition, .NET Standard 1.x is distributed as a granular set of NuGet packages, which creates a large package dependency graph and results in a lot of packages being downloaded when the project is built.
For more information, see What is the downside of targeting .NET Standard 1.x?.
Recommended action
Update your TargetFramework property to netstandard2.0 or netstandard2.1.
If you must stay on an older .NET Standard version, you can set <CheckNotRecommendedTargetFramework> to false in your project file (for example, .csproj file) or Directory.Build.props file to skip the target framework version check:
<PropertyGroup>
...
<CheckNotRecommendedTargetFramework>false</CheckNotRecommendedTargetFramework>
</PropertyGroup>
Alternatively, you can suppress the warning using the <NoWarn> property in your project file:
<PropertyGroup>
...
<!-- Disable "Targeting .NET Standard prior to 2.0 is no longer recommended." warning -->
<NoWarn>$(NoWarn);NETSDK1215</NoWarn>
</PropertyGroup>
Affected APIs
N/A
