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The .NET Framework includes a large class library called the Framework Class Library and provides language interoperability across multiple programming languages.

.NET is a free, cross-platform, open-source developer platform for building many different types of applications. The .NET Framework is the original implementation of .NET. It supports running websites, services, desktop apps and more on Windows.

With .NET, you can use multiple languages, editors, and libraries to build for web, mobile, desktop, gaming, and IoT.

You can write .NET apps in C#, F#, or Visual Basic.

• C# is a simple, modern, object-oriented and type-safe programming language.
• F# is a cross-platform, open source functional programming language for .NET. It also includes object-oriented and imperative programming.
• Visual Basic is an accessible language with a simple syntax for building type-safe, object-oriented apps.

Driving time

The runtime includes everything you need to run existing apps/programs built with the .NET Framework.

Developer package

The developer kit is used by software developers to create applications that run on the .NET Framework, typically using Visual Studio.

What is new

.NET 7 is the successor to .NET 6 and focuses on being unified, modern, simple and fast. .NET 7 will be supported for 18 months as a standard-term support (STS) release (formerly known as a current release).

This article lists the new features in .NET 7 and provides links to more detailed information about each.

To find all the .NET articles that have been updated for .NET 7, see .NET Docs: What’s New for the .NET 7 Release.

Performance

Performance is a key focus of .NET 7, and all features are designed with performance in mind. In addition, .NET 7 includes the following improvements aimed solely at performance:

• On-stack replacement (OSR) is a supplement to layered compilation. It allows the runtime to modify the code executed by a method that is running in the middle of its execution (that is, while it is “on the stack”). Long-running methods can switch to more optimized versions mid-execution.
• Profile Driven Optimization (PGO) now works with OSR and is easier to enable (by adding genuine to your project file). PGO can also instrument and optimize several things, for example delegates.
• Improved code generation for Arm64.
• Native AOT produces a standalone executable in the target platform’s file format with no external dependencies. It is completely native, without IL or JIT, and provides fast startup time and a small, self-contained deployment. In .NET 7, Native AOT focuses on console apps and requires apps to be trimmed.
• Performance improvements to the Mono runtime, which powers Blazor WebAssembly, Android and iOS apps.

For a detailed look at many of the performance-focused features that make .NET 7 so fast, see the Performance Improvements in .NET 7 blog post.

System.Text.Json serialization

.NET 7 includes improvements to System.Text.Json serialization in the following areas:

• Contract customization gives you more control over how types are serialized and deserialized. For more information, see Customize a JSON contract.
• Polymorphic serialization for user-defined type hierarchies. For more information, see Serialize properties for derived classes.
• Support for required members, which are properties that must be present in the JSON payload for deserialization to succeed. For more information, see Required properties.

For information about these and other updates, see the What’s new in System.Text.Json in .NET 7 blog post.

Generic mathematics

• .NET 7 and C# 11 include innovations that allow you to perform mathematical operations generically—that is, without having to know exactly what type you’re working with. For example, if you wanted to write a method that adds two numbers, you previously had to add a method overload for each type. Now you can write a single, generic method, where the type parameter is constrained to be a number-like type. For more information, see the Generic Math article and the Generic Math blog post.

Regular expression

.NET’s regular expression library has seen significant functional and performance improvements in .NET 7:

• The new RegexOptions.NonBacktracking option enables matching using an approach that avoids backtracking and guarantees linear-time processing over the length of the input data. The non-backtracking engine cannot be used in a right-to-left search and has a few other limitations, but is fast for all regular expressions and inputs.
• Regular expression source generators are new. Source generators build an engine optimized for your pattern at compile time, providing performance benefits. The output source is part of your project, so you can view and debug it. Additionally, a new source generator diagnostic SYSLIB1045 alerts you to places you use Regex that can be converted to the source generator. For more information, see Source Generators for .NET Regular Expressions.
• For case-insensitive searches, .NET 7 includes major performance gains. The gain comes because specifying RegexOptions.IgnoreCase no longer calls ToLower on every character in the pattern and on every character in the input. Instead, all casing-related work is done when the Regex is constructed.
• Regex now supports spans for some APIs. The following new methods have been added as part of this support:
• Regex.EnumerateMatches
• Regex.Count
• Regex.IsMatch(ReadOnlySpan) (and a few other overloads)

For more information about these and other improvements, see the Regular Expression Improvements in .NET 7 blog post.

Full release notes can be found here.