Using .NET 9 with this book

Microsoft will release .NET 9 at the .NET Conf 2024 on Tuesday, November 12, 2024, one week after the US Presidential election on November 5. Many readers will want to use this book with .NET 9, so this section explains how.

At the time of publishing in July 2024, .NET 9 is already available in preview, or you can wait for the final version in November 2024. But beware because once you install a .NET 9 SDK, then it will be used by default for all .NET projects unless you override it using a global.json file. You can learn more about doing this at the following link: https://learn.microsoft.com/en-us/dotnet/core/tools/global-json.

You can easily continue to target the .NET 8 runtime while installing and using future C# compilers, as shown in Figure 1.4 and illustrated in the following list:

1. November 2023 onwards: Install .NET SDK 8.0.100 or later and use it to build projects that target .NET 8 and use the C# 12 compiler by default. Every month, update to .NET 8 SDK patches on the development computer and update to .NET 8 runtime patches on any deployment computers.
2. February to October 2024: Optionally, install .NET SDK 9 previews each month to explore the new C# language and .NET library features. Note that you won’t be able to use new library features while targeting .NET 8. Read the monthly announcement posts to find out about the new features in that preview, found at the following link: https://github.com/dotnet/core/discussions/9234.
3. November 2024 onwards: Install .NET SDK 9.0.100 or later and use it to build projects that continue to target .NET 8 and use the C# 13 compiler for its new features. You will be using a fully supported SDK and fully supported runtime. You can also use new features in EF Core 9 because it will continue to target .NET 8.
4. February to October 2025: Optionally, install .NET 10 previews to explore new C# language and .NET library features. Start planning if any new library and ASP.NET Core features in .NET 9 and .NET 10 can be applied to your .NET 8 projects when you are ready to migrate.
5. November 2025 onwards: Install .NET 10.0.100 SDK or later and use it to build projects that target .NET 8 and use the C# 14 compiler. You could migrate your .NET 8 projects to .NET 10 since it is a long-term support (LTS) release. You have until November 2026 to complete the migration when .NET 8 reaches end-of-life.

Figure 1.4: Targeting .NET 8 for long-term support while using the latest C# compilers

When deciding to install a .NET SDK, remember that the latest is used by default to build any .NET projects. Once you’ve installed a .NET 9 SDK preview, it will be used by default for all projects, unless you force the use of an older, fully supported SDK version like 8.0.100 or a later patch.

To gain the benefits of whatever new features are available in C# 13, while still targeting .NET 8 for long-term support, modify your project file, as shown highlighted in the following markup:

<Project Sdk="Microsoft.NET.Sdk">
 
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <LangVersion>13</LangVersion> <!--Requires .NET 9 SDK GA-->
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
</Project>