What’s New in .NET 9: A Simple Guide for Developers

Introduction

.NET 9 has arrived with a focus on cloud-native applications, performance improvements, and developer productivity. This release is packed with updates for runtime, libraries, tools, and frameworks like ASP.NET Core, .NET MAUI, and Entity Framework Core. Let’s dive into the features in simple language to help you get started.

Core Platform Updates

Runtime Improvements

New Feature Switch System

The .NET 9 runtime introduces a sophisticated attribute model for feature switches with enhanced trimming support. This system allows libraries to:

• Define toggleable functionality areas
• Maintain better control over feature availability
• Optimize application size through improved trimming

Advanced Garbage Collection

The new garbage collection system brings significant improvements:

• Dynamic adaptation to application size (enabled by default)
• Replaces traditional Server GC
• Optimizes memory management based on real-time usage patterns
• Reduces memory footprint while maintaining performance

Performance Optimizations

Substantial performance improvements include:

• Enhanced loop optimization algorithms
• Smarter inlining capabilities
• Improved Arm64 vectorization
• Optimized code generation for modern hardware
• Reduced memory overhead in common operations

Library Enhancements

System.Text.Json Updates

The JSON handling capabilities have been significantly expanded:

• Full support for nullable reference type annotations
• JSON schema export functionality from .NET types
• Customizable JSON indentation options
• Multi-root JSON value reading from single streams
• Improved performance for large JSON documents
• Better handling of complex object graphs

LINQ Enhancements

New LINQ methods provide more efficient data operations:

• CountBy: Efficiently count elements by key without intermediate collections
• AggregateBy: Perform aggregations by key without GroupBy overhead
• Improved performance for existing LINQ operations
• Better memory utilization in LINQ queries

Collection Improvements

Priority Queue enhancements:

• New Remove method with comprehensive comparison options
• Improved performance for common operations
• Better memory efficiency for large queues

Cryptography Updates

New cryptographic capabilities:

• One-shot hash method on CryptographicOperations
• KMAC algorithm implementation
• Enhanced security features
• Improved performance for common cryptographic operations

Reflection Capabilities

The new PersistedAssemblyBuilder brings:

• Ability to save emitted assemblies
• Full PDB support for debugging
• Symbol information generation
• Enhanced debugging capabilities for generated code

Artificial Intelligence Integration

AI Building Blocks

Microsoft.Extensions.AI

New unified C# abstractions for AI services:

• Seamless integration with language models
• Embedding support
• Vector store capabilities
• Flexible middleware options

Tensor Operations

TensorPrimitives and Tensor improvements:

• Nearly 200 optimized method overloads
• SIMD-optimized operations
• Generic support for numerical operations
• Zero-copy interop with major AI libraries

ML.NET 4.0 Features

Core Improvements

• Programmatic MLContext configuration
• Stream-based ONNX model loading
• Enhanced DataFrame capabilities
• Advanced tokenization features

Experimental Features

• TorchSharp ports of Llama models
• Phi family model support
• CausalLM pipeline APIs
• Improved model training capabilities

Tokenizer Updates

The Microsoft.ML.Tokenizers library now supports:

• Tiktoken for GPT models
• Llama tokenization
• CodeGen support
• Phi2 tokenization
• WordPiece and Bert implementations

Web Development

ASP.NET Core Updates

Security Enhancements

• Secure-by-default configurations
• Enhanced authentication APIs
• Improved authorization capabilities
• Better HTTPS development support on Linux

Performance Improvements

• Optimized static file handling
• Automatic asset versioning
• Reduced memory usage
• Faster startup times

Blazor Updates

• New application templates
• Improved component rendering
• Enhanced reconnection handling
• Better server-side performance

API Improvements

• Built-in OpenAPI document generation
• Enhanced native AOT support
• Improved API versioning
• Better performance for common API operations

Mobile and Desktop Development

.NET MAUI Enhancements

Performance Updates

• Optimized CollectionView and CarouselView
• Improved control lifecycle management
• Better memory utilization
• Enhanced startup performance

New Controls and Features

• Windows TitleBar control
• HybridWebView for web content
• Enhanced keyboard support
• Improved application lifecycle events

Platform-Specific Improvements

• iOS and Mac Catalyst optimizations
• Windows-specific enhancements
• Better cross-platform consistency
• Improved native feature access

Development Tools and SDK

SDK Improvements

Workload Management

• Unified workload versioning
• Better version control
• Simplified updates
• Enhanced compatibility

Testing and Security

• Parallel test execution
• Comprehensive security audits
• Improved build logging
• Version mismatch detection

Language Updates

C# 13 Features

• params collections
• New lock semantics
• Escape sequence improvements= \e
• Method group enhancements
• ref locals and unsafe contexts in iterators and async methods
• ref struct capabilities
• field backed properties (preview)

F# 9 Enhancements

• Nullable reference types
• Discriminated union improvements
• Enhanced active patterns
• REPL improvements
• Collection functions
• C# collection expression support

Data Access and Entity Framework

Entity Framework Core Updates

Azure Cosmos DB Integration

• Improved NoSQL support
• Better performance
• Enhanced query capabilities
• Optimized data operations

Performance Improvements

• Steps toward AOT compilation
• Pre-compiled queries
• Reduced memory usage
• Faster query execution

.NET Aspire

Cloud-Native Application Development

Dashboard Improvements

• Enhanced monitoring capabilities
• Better resource management
• Improved visualization
• Real-time updates

Integration Features

• New service integrations
• Flexible APIs
• Enhanced development experience
• Better production readiness

Best Practices and Migration

Upgrading to .NET 9

Preparation Steps

1. Review existing codebase compatibility
2. Update dependencies
3. Test application functionality
4. Deploy updates systematically

Migration Considerations

• Review breaking changes
• Update deprecated features
• Test performance impacts
• Verify security implications

Conclusion

.NET 9 is packed with features that cater to developers building modern apps. Whether you’re working on cloud-native projects, AI solutions, or web apps, this release brings tools to make your job easier, faster, and more efficient.

Whether you're building web applications, mobile apps, or AI-powered solutions, .NET 9 offers compelling reasons to upgrade. The improved performance, enhanced security, and new features across all areas of the framework make it a worthy upgrade for existing projects and an excellent choice for new development efforts.

Getting Started

To begin working with .NET 9:

1. Download the latest SDK from Microsoft's website
2. Review the official documentation
3. Test your existing applications for compatibility
4. Start exploring the new features in a development environment