Exploring .NET 11 Preview 4: Key Updates and New Features

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Introduction

The .NET team has released .NET 11 Preview 4, marking another milestone in the evolution of the platform. This preview brings significant enhancements across the runtime, SDK, libraries, ASP.NET Core, .NET MAUI, C#, and Entity Framework Core. Developers can now download and test these improvements, which include long-awaited library updates, performance optimizations, and new tooling capabilities. Below, we break down the most notable changes in each area.

Libraries: Major Overhaul of Core Components

This release introduces the most substantial update to the Process class in years, alongside new streaming APIs for compression and improved floating-point support. Key highlights include:

• Process class enhancements – The System.Diagnostics.Process API receives a major refresh, providing better performance and usability for process management tasks.
• Span-based compression APIs – New overloads for DeflateStream, ZLibStream, and GZipStream now accept ReadOnlySpan<byte> and Span<byte>, enabling zero-allocation encoding and decoding.
• Floating-point hex formatting – Developers can format float and double values as hexadecimal strings (e.g., 0x1.99999ap+4), and parse such strings back, using methods like ToString("X") and Parse(style).
• System.Text.Json improvements – Enhanced serialization options and performance tweaks for JSON handling.

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Runtime: Async Compilation and JIT Optimizations

The .NET runtime itself has been recompiled with runtime-async support, enabling asynchronous calls in low-level infrastructure. Additionally, the JIT compiler gains new optimizations:

• Runtime libraries compiled with runtime-async – Core libraries now leverage asynchronous methods internally, potentially reducing thread-blocking and improving scalability.
• JIT optimizations – The just-in-time compiler produces more efficient machine code, particularly for hot paths.
• Hardware intrinsics and code generation – Expanded use of CPU-specific instructions (e.g., AVX-512) for better performance in compute-intensive workloads.

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SDK: Enhanced Tooling for Mobile and Shell

The .NET SDK preview delivers developer-experience improvements, especially for mobile projects and command-line operations:

• Device selection in dotnet watch – When debugging .NET MAUI or mobile apps, developers can now choose a specific device (emulator or physical) directly from the watch command.
• Fish shell completions – The .NET CLI now provides tab completions for Fish shell, joining existing support for Bash, Zsh, and PowerShell.
• Automatic current-directory fallback – Commands like dotnet reference will now use the current directory if no project file is explicitly specified.
• Telemetry switch to OpenTelemetry – CLI telemetry has moved from Application Insights to OpenTelemetry, aligning with industry standards.

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C#: Cleaner Diagnostics and Build Caching

Two targeted improvements enhance the C# developer experience:

• Better diagnostics for shebang directives – Misplaced #! lines (e.g., a shebang not at the start of a file) now produce clearer error messages.
• Opt-in compilation cache for VBCSCompiler – The Visual Basic and C# compiler server can cache compiled outputs, reducing incremental build times. This feature is opt-in and can be enabled via project settings.

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ASP.NET Core: OpenAPI, Blazor, and MCP Server Template

Web developers gain several new capabilities in ASP.NET Core:

• HTTP QUERY in OpenAPI – The generated OpenAPI documents now correctly represent the QUERY HTTP method, useful for read-only endpoints.
• SupplyParameterFromTempData for Blazor – Blazor components can now easily receive data from TempData via a new attribute.
• Server-initiated Blazor Server circuit pause – Servers can temporarily pause a Blazor Server circuit, reducing resource usage during idle periods.
• MCP Server template ships with SDK – A new project template for creating MCP (Model Context Protocol) servers is included out of the box, simplifying AI-integration scenarios.

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.NET MAUI: Mobile Debugging with dotnet watch

Mobile developers will appreciate expanded support for hot reload and debugging:

• Android – dotnet watch now works with Android projects, allowing live code changes on emulators and devices.
• iOS – Similarly, iOS projects gain dotnet watch support, enabling faster iteration on Apple devices.

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Entity Framework Core: Vectors, JSON, and Temporal Periods

The ORM framework introduces several database-focused features:

• Approximate vector search for SQL Server 2025 – EF Core now supports approximate nearest-neighbor search using vector indexes, targeting SQL Server 2025.
• Fully integrated JSON mapping – JSON columns are now a first-class part of the relational model, making it easier to work with NoSQL-like data within SQL databases.
• Temporal period properties – Temporal table period columns (e.g., SysStartTime, SysEndTime) can be mapped to ordinary CLR properties, simplifying history queries.
• Default configuration via dotnet-ef.json – The dotnet ef tool reads default settings from a dotnet-ef.json file, streamlining project setup.

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Getting Started with .NET 11 Preview 4

Ready to try the new features? Follow these steps:

1. Download the .NET 11 Preview 4 SDK from the official .NET download page.
2. If you use Visual Studio on Windows, upgrade to the latest Visual Studio 2026 Insider build for full compatibility.
3. Alternatively, use Visual Studio Code with the C# Dev Kit extension for a lightweight development environment.
4. Check the linked release notes for each component to explore detailed changes.

This preview gives you a chance to influence the final .NET 11 release through feedback. Dive in and start building with the latest tools and libraries.

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