.NET 10 LTS and C# 14 Released: What Changes for AI Developers

What Happened#

Microsoft's what's-new documentation groups the release into familiar areas. In the runtime, the JIT improved inlining and method devirtualization, expanded stack allocation, generated better code for struct arguments and improved loop optimizations, while hardware support grew to include AVX10.2 and Native AOT received further enhancements. None of these require code changes, which is why runtime upgrades can lower compute costs without touching application code.

The libraries picked up post-quantum cryptography support with ML-DSA, HashML-DSA and Composite ML-DSA, along with AES KeyWrap with Padding. System.Text.Json gained options to disallow duplicate properties, stricter serialization settings and PipeReader support, and networking added WebSocketStream and TLS 1.3 for macOS clients. ASP.NET Core focused on Blazor WebAssembly preloading, automatic memory pool eviction, improved form validation, better diagnostics and passkey support, while EF Core added named query filters and improved Azure Cosmos DB support.

The SDK changes are the most visible day to day. dotnet test supports Microsoft.Testing.Platform, dotnet tool exec runs a tool without installing it, and the new dnx script shortens that to a single command. Console apps can produce container images, and --cli-schema exposes the CLI's structure for tooling. File-based apps let you run a single .cs file with dotnet run app.cs, pull in packages and SDKs with #:package and #:sdk directives, and publish with Native AOT by default.

C# 14 rounds out the release. The headline feature is extension members, which let you declare extension properties and static extension members inside an extension block:

public static class EnumerableExtensions
{
    extension<TSource>(IEnumerable<TSource> source)
    {
        public bool IsEmpty => !source.Any();
    }
}

Other additions include the field keyword for accessing a property's compiler-generated backing field, null-conditional assignment such as customer?.Order = GetCurrentOrder();, nameof with unbound generic types like List<>, implicit span conversions, parameter modifiers on lambdas without explicit types, partial constructors and events, and user-defined compound assignment operators.