.NET 10 Released: Complete Guide to New Features and Performance Improvements in 2025

The .NET ecosystem continues to evolve with the release of .NET 10, the latest Long-Term Support (LTS) version announced at .NET Conf 2025. This release brings groundbreaking features, significant performance improvements, and innovations that will transform how developers build modern applications. With up to 3 years of support, .NET 10 represents a major milestone for the 7 million .NET developers worldwide.

Table of Contents

• What's New in .NET 10 Overview
• .NET 10 Runtime and Framework Versions
• File-Based Applications: Revolutionary Development Approach
• C# 14: Complete Language Features Guide
• Aspire Rebranding and Cloud-Native Development
• ASP.NET Core 10: Performance and WebAuthn Support
• Blazor Improvements: Hot Reload and Persistent State
• Server-Sent Events (SSE): Real-Time Communication Made Easy
• Performance Gains Across the Board
• Conclusion

What's New in .NET 10 Overview

.NET 10 arrives as the latest Long-Term Support (LTS) release with up to 3 years of support, making it ideal for enterprise applications requiring stability and extended maintenance. The release showcases Microsoft's commitment to the open-source ecosystem, with .NET ranking in the top five most active open-source projects globally, supported by more than 68,000 contributors.

Key Highlights

• LTS release with 3 years of support
• 7 million .NET developers worldwide
• 68,000+ contributors to .NET repositories
• Introduction of .NET Agent Framework (unification of Semantic Kernel and Autogen)
• New application type: AI agents for modern intelligent applications

The .NET ecosystem now supports a comprehensive range of development scenarios including Microsoft Azure integration, cross-platform development, and the exciting new AI agent development capabilities.

.NET 10 Runtime and Framework Versions

Understanding the version landscape of .NET 10 is crucial for developers planning migrations and new projects. .NET 10 represents a unified platform that consolidates multiple frameworks and runtimes under a single version number.

Version Numbers and Components

.NET 10.0 includes the following major components:

• .NET Runtime 10.0 - Core runtime engine for executing .NET applications
• ASP.NET Core 10.0 - Web application framework
• .NET SDK 10.0.x - Development tools and compilers
• C# 14 - Latest version of the C# language
• F# 9 - Updated functional programming language
• Entity Framework Core 10.0 - Object-relational mapping (ORM) framework

Framework Unification

.NET 10 continues the unification strategy that began with .NET 5, consolidating:

• .NET Framework (legacy Windows-only framework)
• .NET Core (cross-platform framework)
• Xamarin/Mono (mobile development platform)

This unified approach means developers work with a single framework that targets:

• Windows (desktop and server applications)
• Linux (server applications, containers, cloud)
• macOS (desktop and server applications)
• iOS and Android (mobile applications via .NET MAUI)
• Web browsers (via Blazor WebAssembly)

Runtime Architecture

The .NET 10 runtime includes several key components:

CoreCLR (Common Language Runtime)

• Garbage collection (GC) improvements
• JIT (Just-In-Time) compiler optimizations
• Native AOT (Ahead-of-Time) compilation support
• Cross-platform execution engine

Base Class Library (BCL)

• Core types and collections
• File I/O and networking
• Cryptography and security
• Threading and async operations

Framework Libraries

• ASP.NET Core for web development
• Entity Framework Core for data access
• ML.NET for machine learning
• .NET MAUI for cross-platform UI

Target Framework Monikers (TFMs)

When building .NET 10 applications, you'll use these TFMs in your project files:

• net10.0 - Standard .NET 10 applications
• net10.0-windows - Windows-specific features
• net10.0-android - Android applications
• net10.0-ios - iOS applications
• net10.0-maccatalyst - macOS Catalyst apps

Support Timeline

As an LTS release, .NET 10 follows Microsoft's support policy:

• Standard Support: 3 years from release date
• Security updates: Critical fixes throughout support period
• Long-term stability: Ideal for production enterprise applications
• Migration path: Direct upgrade from .NET 6, 8, and 9

Version Compatibility

.NET 10 maintains backward compatibility with:

• .NET Standard 2.0 and 2.1 libraries
• Existing NuGet packages built for previous .NET versions
• Most .NET Framework APIs (when targeting Windows)

This comprehensive version structure ensures developers can build modern, cross-platform applications while maintaining compatibility with existing codebases.

File-Based Applications: Revolutionary Development Approach

One of the most anticipated features in .NET 10 is file-based applications, which fundamentally changes how developers can create and run .NET programs. This feature eliminates the need for solution and project files for simple applications.

How File-Based Applications Work

Instead of creating a full solution structure, you can now create a simple .cs file and run it directly:

Example: Basic Hello World

Console.WriteLine("Hello, World!");

Run it with:

dotnet run hello-world.cs

Console Arguments Support

File-based applications support command-line arguments seamlessly:

Console.WriteLine($"Hello, {args[0]}!");

Execute with:

dotnet run hello-world.cs John

Direct NuGet Package References

The revolutionary new syntax allows you to reference NuGet packages directly within your .cs file:

#:package Silo

// Now use types from the Silo package

This inline package reference eliminates the need for separate package management files for simple scripts and applications.

Converting to Full Projects

When your file-based application grows, convert it to a traditional project structure:

dotnet project convert

Use Cases for File-Based Applications

• Quick prototyping and experimentation
• Scripting and automation tasks
• Learning and teaching C# fundamentals
• Single-file utilities and tools
• Code samples and demonstrations

This feature represents an entirely new paradigm for .NET development, making it more accessible and reducing friction for beginners while maintaining power for experienced developers.

C# 14: Complete Language Features Guide

With .NET 10 comes C# 14, introducing powerful language features that make code more concise and expressive.

1. Null Conditional Assignment Operator

This feature simplifies null-safe assignments, reducing boilerplate code significantly.

Before C# 14:

public class Developer
{
    public int Age { get; set; }
}

public Developer? CreateDeveloper(int age)
{
    if (age > 0)
    {
        return new Developer { Age = age };
    }
    return null;
}

// Usage
var developer = CreateDeveloper(25);
if (developer != null)
{
    developer.Age = 30;
}

With C# 14:

var developer = CreateDeveloper(-5);
developer?.Age = 30; // Safe assignment - no crash if null

The ?. operator before the assignment ensures the operation only executes if the object is not null, eliminating the need for explicit null checks.

2. Field-Backed Properties with field Keyword

Previously, implementing property validation required explicit backing fields. C# 14 introduces the field keyword to simplify this pattern.

Before C# 14:

public class Time
{
    private double _hours; // Explicit backing field

    public double Hours
    {
        get => _hours;
        set
        {
            if (value < 0)
                throw new ArgumentException("Hours cannot be negative");
            _hours = value;
        }
    }
}

With C# 14:

public class Time
{
    public double Hours
    {
        get => field;
        set
        {
            if (value < 0)
                throw new ArgumentException("Hours cannot be negative");
            field = value;
        }
    }
}

The field keyword automatically creates and references the backing field, reducing code clutter while maintaining validation logic.

3. Extension Fields

C# 14 introduces extension fields, a groundbreaking feature that allows you to add fields (not just methods) to existing types.

Syntax and Usage:

public extension UserExtensions for User
{
    private string _cachedFullName;

    public string GetCachedFullName()
    {
        if (_cachedFullName == null)
        {
            _cachedFullName = $"{this.FirstName} {this.LastName}";
        }
        return _cachedFullName;
    }
}

This feature enables:

• Adding stateful behavior to existing types
• Caching computed values
• Implementing decorators without inheritance
• Extending third-party libraries

4. Enhanced Collection Expressions

C# 14 expands collection expressions with more powerful syntax:

Spread Operator in Collections:

int[] numbers1 = [1, 2, 3];
int[] numbers2 = [4, 5, 6];
int[] combined = [..numbers1, ..numbers2, 7, 8];
// Result: [1, 2, 3, 4, 5, 6, 7, 8]

Dictionary Collection Expressions:

var config = new Dictionary<string, string>
{
    ["host"] = "localhost",
    ["port"] = "8080"
};

// C# 14 simplified syntax
var config = ["host": "localhost", "port": "8080"];

5. Improved Pattern Matching

C# 14 adds list patterns with slice patterns:

int[] numbers = [1, 2, 3, 4, 5];

var result = numbers switch
{
    [1, .. var middle, 5] => $"Starts with 1, ends with 5, middle: {string.Join(",", middle)}",
    [var first, ..] => $"First element: {first}",
    [] => "Empty array"
};

6. Primary Constructors for All Classes

C# 14 extends primary constructors (introduced in C# 12 for records) to all class types:

public class Logger(ILogWriter writer, string category)
{
    public void Log(string message)
    {
        writer.Write($"[{category}] {message}");
    }
}

// Usage
var logger = new Logger(consoleWriter, "App");

Benefits:

• Reduces boilerplate constructor code
• Automatic parameter capturing
• Cleaner dependency injection
• More concise class definitions

7. Params Collections Enhancement

C# 14 allows params with any collection type, not just arrays:

public void ProcessItems(params IEnumerable<string> items)
{
    foreach (var item in items)
    {
        Console.WriteLine(item);
    }
}

// Usage
ProcessItems("a", "b", "c");
ProcessItems(new List<string> { "x", "y" });

C# 14 Language Version Summary

These language improvements make C# code more readable, maintainable, and less prone to common errors while maintaining backward compatibility with previous versions.

Aspire Rebranding and Cloud-Native Development

.NET Aspire, now officially renamed to simply Aspire, receives significant updates with version 13. Aspire is Microsoft's opinionated framework for building cloud-native, distributed applications.

What is Aspire?

Aspire provides:

• Orchestration for multi-project applications
• Service discovery and configuration
• Telemetry and monitoring out-of-the-box
• Container orchestration for development
• Cloud deployment integration

New Features in Aspire v13

• Enhanced developer experience
• Improved telemetry and observability
• Better integration with Azure services
• Streamlined deployment workflows
• Enhanced testing capabilities

Aspire simplifies building microservices architectures and distributed systems, making cloud-native development more accessible to .NET developers.

ASP.NET Core 10: Performance and WebAuthn Support

ASP.NET Core in .NET 10 continues the tradition of performance improvements across all web frameworks and features.

Performance Improvements

• Minimal APIs - faster routing and endpoint resolution
• Blazor - improved rendering performance
• SignalR - reduced latency for real-time connections
• Middleware pipeline - optimized request processing
• JSON serialization - faster serialization/deserialization

WebAuthn and Passkey Support

A standout feature is the native support for WebAuthn and passkeys, enabling:

• Passwordless authentication for web applications
• Biometric authentication (fingerprint, facial recognition)
• Hardware security keys (YubiKey, etc.)
• Enhanced security over traditional passwords
• Improved user experience with faster logins

WebAuthn represents the future of web authentication, providing both better security and user convenience.

Implementation Benefits

• Built-in security best practices
• Cross-platform compatibility
• Reduced authentication-related vulnerabilities
• Compliance with modern security standards

Blazor Improvements: Hot Reload and Persistent State

Blazor, Microsoft's framework for building interactive web UIs with C#, receives significant enhancements in .NET 10.

Enhanced Hot Reload

Hot reload has been completely reimagined for .NET 10, addressing long-standing developer pain points:

Previous Issues:

• Inconsistent behavior with large applications
• Long reload times (up to 40 seconds for simple changes)
• Frequent need to restart entire application
• Dependence on change complexity

Improvements in .NET 10:

• Reduced reload time - simple UI changes now reload in ~3 seconds (down from 40 seconds)
• More reliable across different project sizes
• Faster feedback loops for developers
• Improved incremental compilation

Persistent Blazor State

A game-changing feature for Blazor Server applications is persistent state management. This addresses a critical challenge in Blazor Server apps where state is lost when connections drop.

Problem Solved:

• User disconnects from Blazor Server app
• Reconnects to the same application
• State is preserved instead of being reset

Use Cases:

• Form data preservation during network interruptions
• Shopping cart persistence in e-commerce applications
• User session continuity in line-of-business apps
• Improved user experience during temporary disconnections

Additional Blazor Enhancements

• Performance optimizations across the framework
• Improved component rendering
• Better server-side rendering (SSR) capabilities
• Enhanced interactivity options

These improvements make Blazor an even more compelling choice for building modern web applications with C#.

Server-Sent Events (SSE): Real-Time Communication Made Easy

One of the coolest features in .NET 10 is native support for Server-Sent Events (SSE), enabling unidirectional real-time communication from server to client using standard HTTP.

What are Server-Sent Events?

SSE allows servers to push updates to web clients over a persistent HTTP connection without the complexity of WebSockets or SignalR when bidirectional communication isn't needed.

Implementing SSE in .NET 10

Creating a Server-Sent Events Endpoint:

app.MapGet("/live-orders", async (CancellationToken ct) =>
{
    return TypedResults.ServerSentEvents(GetOrders(ct));
});

async IAsyncEnumerable<SseItem<FoodOrder>> GetOrders(
    [EnumeratorCancellation] CancellationToken ct)
{
    while (!ct.IsCancellationRequested)
    {
        await Task.Delay(1000, ct);

        yield return new SseItem<FoodOrder>(
            data: FoodOrderGenerator.CreateOrder(),
            eventType: "order",
            reconnectionInterval: TimeSpan.FromMinutes(1)
        );
    }
}

public record FoodOrder(string Name, decimal Price);

Consuming SSE in a Web Browser

JavaScript Client Implementation:

// Create EventSource connection
const eventSource = new EventSource('/live-orders');

// Listen for specific event types
eventSource.addEventListener('order', (event) => {
    const order = JSON.parse(event.data);

    // Update UI with new order
    const orderElement = document.createElement('li');
    orderElement.textContent = `${order.name} - $${order.price}`;
    document.getElementById('orders-list').appendChild(orderElement);
});

// Handle errors
eventSource.onerror = (error) => {
    console.error('Connection failed:', error);
};

SSE Features in .NET 10

• Typed results with SseItem<T>
• Event typing for client-side filtering
• Reconnection intervals configuration
• Native browser support - no additional libraries needed
• Automatic reconnection on connection drops

When to Use SSE vs. Alternatives

Use Server-Sent Events when:

• You need unidirectional data flow (server � client)
• Building live dashboards and monitoring tools
• Implementing stock tickers or price updates
• Creating notification systems
• Showing real-time logs or activity feeds
• Building live order tracking systems

Use SignalR/WebSockets when:

• You need bidirectional communication
• Building chat applications
• Creating collaborative editing tools
• Implementing multiplayer games

Advantages of SSE

• Simpler than WebSockets for one-way communication
• Built on standard HTTP - works with existing infrastructure
• Automatic reconnection handled by browser
• Event typing for message filtering
• No additional dependencies required

SSE in .NET 10 provides an elegant solution for real-time server-to-client communication without the overhead of more complex alternatives.

Performance Gains Across the Board

As with every .NET release, .NET 10 delivers significant performance improvements that benefit all applications automatically upon upgrade.

Performance Improvements Include

Runtime Performance:

• Faster garbage collection (GC)
• Improved JIT (Just-In-Time) compilation
• Enhanced SIMD (Single Instruction, Multiple Data) support
• Better memory allocation patterns

Framework Performance:

• Optimized collections and LINQ operations
• Faster string operations and parsing
• Improved async/await performance
• Enhanced JSON serialization/deserialization

Web Performance:

• Reduced HTTP request processing overhead
• Faster minimal API routing
• Improved middleware pipeline efficiency
• Better connection pooling

Real-World Impact

Simply upgrading from .NET 9 to .NET 10 can result in:

• Faster application execution
• Reduced memory consumption
• Lower CPU utilization
• Improved scalability

Cloud Cost Benefits: For applications running on consumption-based cloud plans (Azure Functions, AWS Lambda), these performance improvements translate directly to:

• Lower execution costs
• Reduced resource consumption
• Better cost efficiency at scale

Performance Documentation

Stephen Toub's comprehensive 250-page blog post details the extensive performance improvements in .NET 10, covering:

• Micro-optimizations throughout the framework
• Benchmarks and comparisons
• Technical implementation details
• Real-world scenario improvements

These performance gains ensure that .NET remains one of the fastest and most efficient platforms for building modern applications.

Conclusion

.NET 10 represents a significant leap forward for the .NET ecosystem, introducing revolutionary features like file-based applications, powerful C# 14 language enhancements, and native Server-Sent Events support. Combined with the traditional performance improvements and enhanced Blazor development experience, .NET 10 solidifies Microsoft's commitment to developer productivity and application performance.

Key Takeaways

1. File-based applications lower the barrier to entry for .NET development
2. C# 14 introduces practical language features for cleaner, safer code
3. Aspire (formerly .NET Aspire) simplifies cloud-native development
4. Server-Sent Events provide elegant real-time communication
5. Blazor improvements enhance web development productivity
6. Performance gains deliver automatic benefits to all applications
7. WebAuthn support enables modern, passwordless authentication

Getting Started with .NET 10

1. Download .NET 10 SDK from the official Microsoft website
2. Upgrade existing projects to target .NET 10
3. Explore C# 14 features in your codebase
4. Experiment with file-based applications for scripts
5. Implement Server-Sent Events for real-time features
6. Review performance improvements in your applications

With 3 years of LTS support, now is the perfect time to adopt .NET 10 for both new and existing projects. The combination of stability, performance, and innovative features makes it an exciting release for the 7 million .NET developers worldwide.

What's your favorite .NET 10 feature? Share your thoughts and experiences with the new release in the comments below. Whether you're excited about file-based applications, C# 14 language features, or the performance improvements, the .NET community would love to hear your perspective on this major release.

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