What’s New in .NET 9: Everything You Need to Know

.NET 9 is finally here, and it’s packed with exciting updates that make it easier than ever to build high-performance, modern applications. From cloud-native enhancements to AI tools and developer productivity features, this release has something for everyone. Let’s dive into the highlights of .NET 9 and explore what makes it a game-changer for developers.

Built for Performance and Flexibility

.NET 9 is designed with cloud-native applications and developer productivity in mind. It builds on the strengths of its predecessor, .NET 8, but takes things to the next level with better tooling, enhanced runtime, and more robust libraries. This release is an STS (standard-term support) version, which means it will receive 18 months of official support—enough time to build and refine your next big project.

.NET Runtime: Smarter, Faster, Stronger

The runtime in .NET 9 introduces a range of improvements:

• Feature Switch Attributes: Easily toggle functionality in libraries with built-in support for trimming.
• Dynamic Garbage Collection: Garbage collection now adapts to your app’s size automatically, improving performance without manual tuning.
• Performance Gains: Enhancements like loop optimizations and better Arm64 support mean faster apps, especially for CPU-intensive tasks.

These updates ensure your apps run faster and smarter out of the box.

Libraries That Do More

.NET 9’s libraries are more capable and developer-friendly than ever:

• JSON Handling: New options for working with JSON, including customizable indentation and support for nullable reference types.
• Better LINQ: New CountBy and AggregateBy methods simplify key-based aggregation.
• Improved Collections: The PriorityQueue now allows you to update item priorities seamlessly.
• Safer TimeSpan: New methods prevent errors caused by floating-point imprecision when working with time intervals.

Whether you’re building APIs, handling large datasets, or working with cryptography, .NET 9’s libraries have you covered.

Tools You’ll Love: Updates to the SDK

The .NET 9 SDK introduces some fantastic tools to make development smoother:

• Workload Sets: Keep your workloads consistent across versions until you’re ready to update.
• Smarter Unit Testing: Run tests in parallel with better MSBuild integration.
• Security by Default: Automatic NuGet security audits ensure both direct and transitive dependencies are safe.

For command-line fans, the new dotnet workload history command lets you track changes to installed workloads—a simple but powerful addition.

AI Gets a Boost

AI is at the heart of many modern applications, and .NET 9 doesn’t disappoint:

• TensorPrimitives and Tensor<T>: These new types unlock high-performance AI workflows with efficient data manipulation.
• ML.NET 4.0: Build smarter apps with new options for tokenization, ONNX model support, and experimental features like Llama and Phi pipelines.

With these tools, integrating AI into your .NET apps has never been easier—or more powerful.

ASP.NET Core: Secure and Lightning Fast

ASP.NET Core gets some major upgrades in this release:

• Blazor Improvements: New hybrid templates and smoother server rendering make building interactive apps easier than ever.
• Static File Optimization: Automatic versioning for JavaScript and CSS files ensures your users always get the latest assets.
• OpenAPI and AOT Support: Built-in tools for API documentation and ahead-of-time compilation reduce friction in modern app development.

These updates focus on making apps faster, more secure, and easier to maintain.

.NET MAUI: Better Cross-Platform Apps

For developers building cross-platform apps, .NET MAUI has some exciting new features:

• Performance Upgrades: Faster controls for iOS and Mac Catalyst.
• New Controls: A HybridWebView makes it easy to include JavaScript-enabled content, while the new TitleBar control adds polish to desktop apps.
• Smaller Apps: Native AOT and trimming improvements make your apps leaner and quicker to start.

Whether you’re targeting desktop or mobile, .NET MAUI in .NET 9 makes it easier to create polished, high-performance apps.

C# 13: Simpler, More Intuitive Code

C# 13 arrives with some highly-requested features:

• params Collections: A more natural way to pass variable-length arguments.
• New Escape Sequences: The \e escape sequence makes working with text simpler.
• Partial Properties: Add partial properties to partial classes for cleaner, more maintainable code.

These features focus on making C# even more intuitive and flexible for developers.

Modern Windows Development: WPF and WinForms

Windows desktop development gets some love in .NET 9:

• WPF Enhancements: Support for Fluent design themes and Windows light/dark modes.
• WinForms Updates: Experimental dark mode rendering and asynchronous dialog handling make apps feel modern and responsive.

For developers creating desktop apps, these updates bring modern design and functionality to the forefront.

Why Upgrade to .NET 9?

.NET 9 isn’t just an incremental update—it’s a step forward for the entire ecosystem. Whether you’re building web apps, AI-driven solutions, cross-platform experiences, or desktop applications, this release provides the tools and performance you need to deliver your best work.

Ready to Get Started?

You can download .NET 9 here and start exploring its features today. With so many improvements across the board, there’s no better time to upgrade and see how .NET 9 can elevate your development experience. 🚀