What's New in .NET 10: A Map of the Platform

.NET 10 is the successor to .NET 9 and a long-term support (LTS) release, supported for three years. This concept is a map, not a tutorial: it lists what Microsoft's "What's new in .NET 10" pages say changed in the runtime, the SDK and the libraries, in a few lines each, and points to the concept in this track or in C# Concepts that explains the mechanism. Read it to decide what to study next. ASP.NET Core, EF Core and C# 14 have their own "what's new" pages and are only pointed to here. Every item below was checked against the official pages for the runtime, the SDK and the libraries.

• Planning an upgrade from .NET 8 or 9 and deciding which changes affect your code.
• Finding the deep concept behind a headline feature without reading release notes.
• Telling apart what is on by default (SDK behavior) from what you must opt into.
• Onboarding a team that last used .NET Framework or an older LTS.

Support and versions

.NET 10 is an LTS release with three years of support. Which target to choose for a new project, and how the support calendar works, is in the concept "The .NET Support Lifecycle and Choosing a Target" (dotnet-support-lifecycle-and-choosing-a-target). The language that ships with it is C# 14: field-backed properties, extension blocks, null-conditional assignment and more. The versions-and-preview mechanics live in csharp-language-versions-and-preview-features, and two of the headline features have their own concepts: properties-init-accessors-and-the-field-keyword and extension-members-and-extension-blocks.

Runtime and JIT

The runtime page lists JIT work on struct arguments (promoted members can share a register), loop inversion based on a graph analysis, array interface method devirtualization, a new block layout heuristic and better inlining. Stack allocation grows to small arrays of value types and of reference types, and escape analysis now covers local struct fields and delegates. On Arm64 the new write-barrier default improves GC pauses; the page cites 8% to over 20%. AVX10.2 intrinsics exist but JIT support is disabled by default, because capable hardware was not yet available. NativeAOT also gets small preinitializer improvements. To read how source becomes machine code, see roslyn-il-and-the-jit. For why "structs on the stack, classes on the heap" is only a rule of thumb, see value-types-reference-types-and-boxing.

SDK and CLI

• File-based apps gain publish support, the #:project directive, runtime path access and better shebang handling. They target Native AOT by default, and #:property PublishAot=false turns that off. Deep dive: file-based-apps; the AOT side is in native-aot-and-its-limits.
• One-shot tools. dotnet tool exec runs a tool without installing it, and dnx is a script that forwards to it. Tools can also ship per-RID packages, including the any RID for a portable fallback.
• Noun-first commands. dotnet package add and dotnet reference add join the old verb-first forms, which still work.
• Introspection and shells. --cli-schema prints the command tree as JSON, and dotnet completions script emits native completion scripts for bash, fish, nushell, PowerShell and zsh. CLI commands are also interactive by default in interactive terminals.
• Package pruning. NuGet Audit can prune framework-provided package references for projects targeting .NET 10 or later, which cuts restore work and shrinks deps.json files. See nuget-restore-versions-and-dependency-resolution and assemblies-frameworks-and-the-host-resolver.
• Containers and tests. Console apps can create container images with dotnet publish /t:PublishContainer, ContainerImageFormat selects Docker or OCI, and dotnet test supports Microsoft.Testing.Platform through global.json. The testing track starts at testing-clean-architecture-with-mstest.
• MSBuild tasks. msbuild.exe and Visual Studio 2026 can run tasks built for .NET. Project files are covered in sdk-style-projects-msbuild-and-directory-build-props.

Libraries

• Numeric string ordering. CompareOptions.NumericOrdering makes "2" sort before "10". Deep dive: strings-comparison-culture-and-ordering.
• System.Text.Json. AllowDuplicateProperties, the JsonSerializerOptions.Strict preset, PipeReader overloads for deserialization and ReferenceHandler in JsonSourceGenerationOptions. See system-text-json-serialization-and-options and system-text-json-source-generation-and-utf8jsonreader.
• Async ZIP. ZipArchive.CreateAsync, ZipFile.OpenReadAsync and related methods avoid blocking threads on archive I/O. Background on streams and pipelines: async-io-and-system-io-pipelines.
• Also listed by the libraries page: post-quantum cryptography (ML-DSA, Composite ML-DSA), AES KeyWrap with Padding, WebSocketStream, TLS 1.3 for macOS clients, new ActivitySource and Meter options, Tensor APIs and Windows process groups. No concept here covers them yet.

Other areas

Aspire, ASP.NET Core, EF Core, Windows Forms, WPF and MAUI each have their own page. The overview names named query filters as an EF Core 10 feature; they are explained in global-and-named-query-filters, and JSON columns in json-columns-and-complex-types.

• LTS is a policy, not a reason. Moving from 8 to 10 gets you three years of support, but each item above still needs a test. Measure your own workload before attributing speed to JIT gains.
• Defaults change behavior. A file-based app targets Native AOT, so a package that needs reflection can fail at dotnet run. The fix is one #:property line, but you must know the default exists.
• Pruning can surprise. Smaller deps.json files are good, yet a script that looked for a framework package in the old file may now find nothing.
• A map hides depth. Each bullet here is a headline. The Microsoft pages are the source of truth and keep being edited; this page records what they said when it was written.