.NET 9 New Features for Web Developers Print

Overview

.NET 9 was released in November 2024 as a Standard Term Support (STS) release, supported until May 2026. It brings significant improvements to ASP.NET Core, Blazor, and the runtime.

.NET 9 vs .NET 10

ASP.NET Core 9 Highlights

Blazor Improvements

• Static Server Rendering (SSR): Improved performance for static content
• Enhanced Streaming Rendering: Better user experience during page loads
• Improved Reconnection: Better handling of SignalR disconnections
• WebAssembly Debugging: Enhanced debugging experience

Minimal APIs

• Native AOT Support: Improved Ahead-of-Time compilation
• Better OpenAPI: Enhanced Swagger/OpenAPI integration
• Improved Performance: Faster endpoint routing

SignalR Updates

• Improved Scalability: Better handling of many connections
• Trimming Support: Reduced application size

Runtime Improvements

Performance

• Garbage Collection: Improved memory management
• JIT Compiler: Better code generation
• Native AOT: Enhanced ahead-of-time compilation

JSON Serialization

• Better System.Text.Json performance
• Improved source generator support
• New serialization options

C# 13 Features (with .NET 9)

• Params collections: Use params with any collection type
• New lock type: System.Threading.Lock for better performance
• New escape sequence: e for escape character
• Partial properties: Partial property support in partial classes

Entity Framework Core 9

• LINQ improvements: Better query translation
• Cosmos DB: Enhanced Azure Cosmos DB support
• Performance: Reduced memory allocations
• Migrations: Improved migration tooling

Upgrading from .NET 8

Update Project File:

<TargetFramework>net9.0</TargetFramework>

Update Packages:

dotnet outdated
dotnet restore

Key Considerations:

• Review breaking changes in release notes
• Update NuGet packages to 9.x versions
• Test thoroughly before deploying

When to Use .NET 9

Choose .NET 9 if:

• You want the latest features
• You can update when .NET 10 releases
• Your project benefits from new capabilities

Choose .NET 8 (LTS) or .NET 10 (LTS) if:

• You need long-term support
• Stability is more important than new features
• You prefer less frequent updates

Resources

• Microsoft .NET 9 Documentation
• ASP.NET Core 9 Release Notes