Microsoft has released the third preview of .NET 10, its cross-platform, open-source application development platform, which is expected to ship as a production release in November. .NET 10 Preview 3 introduces several key enhancements, including an AOT-safe constructor for ValidationContext, more powerful C# language extensions, and Blazor WebAssembly improvements.

The new AOT-safe constructor for ValidationContext ensures that developers can use the class in native builds without encountering errors or warnings. This is particularly important, as the existing constructors were marked as unsafe for ahead-of-time (AOT) compilation due to the use of reflection in extracting the DisplayName. With this update, developers can now use ValidationContext in native builds with confidence.

In addition to the AOT-safe constructor, .NET 10 Preview 3 also brings improvements to the standard library, including a deterministic option for the LightGBM trainer in ML.NET. This update exposes LightGBM's deterministic, force_row_wise, and force_cos_wise options, allowing developers to force deterministic training behavior when needed. Furthermore, C# 14 language extensions now support static methods, instance properties, and static properties, with more extension support planned for future releases.

Blazor WebAssembly also receives significant updates in .NET 10 Preview 3. Standalone Blazor WebAssembly apps can now reference static web assets using either a generated import map or a fingerprinted URL. Moreover, response streaming is now enabled by default for HttpClient, which improves performance and reduces memory usage when handling large responses.

The .NET runtime also sees improvements in .NET 10 Preview 3, with an optimization related to block ordering in the JIT compiler. This results in improved code layout and performance. The SDK and CLI also receive updates, with the --interactive flag now enabled by default for all uses of the CLI believed to be interactive.

.NET MAUI (Multi-platform App UI) also benefits from various performance improvements in .NET 10 Preview 3. Additionally, a CancellationToken can now be passed to WebAuthenticator.AuthenticateAsync, enabling programmatic canceling of authentication.

Other notable updates in .NET 10 Preview 3 include OpenAPI support being enabled by default in the ASP.NET Core Web API (native AOT) template, and a focus on quality improvements, experimental runtimes, and build performance on .NET for Android.

This preview builds upon the previous two previews, which introduced features such as allowing callers to choose which encryption and digest algorithms are used to produce the output, and C# 14 with "first-class" support for System.Span and System.ReadOnlySpan in the language.

With .NET 10 expected to ship in November, developers can start testing and providing feedback on these new features and improvements. The release of .NET 10 Preview 3 marks a significant milestone in the development of the .NET platform, and its impact will be closely watched by the developer community.

Developers can download .NET 10 Preview 3 from dotnet.microsoft.com and start exploring the new features and improvements today.