Both .NET 8 and .NET 9 stop getting security patches on November 10, 2026 — same date, despite one being LTS and the other STS. Bumping TargetFramework takes five seconds. Finding out what changed underneath it takes longer: EF Core's query translation, whether one failing BackgroundService blocks every other one from starting, and how SQLite reinterprets a DateTimeOffset it's never seen before. I ran every item on this list myself, on both SDKs side by side, before writing any of it down.

Every provider SDK — OpenAI, Azure OpenAI, Ollama, Anthropic — has its own client, its own message types, its own way of doing tool calling. Microsoft.Extensions.AI collapses all of that behind a single IChatClient interface, with DI-friendly middleware for caching, telemetry, and function invocation built in. Here's how the abstraction actually works.

ASP.NET Core Identity in .NET 10 ships built-in WebAuthn/FIDO2 passkey support. Here's how registration and sign-in actually work under the hood, what MakePasskeyCreationOptionsAsync and PasskeySignInAsync do for you, and where the implementation deliberately stops short of a full WebAuthn library.

Before/after demo for migrating enterprise .NET apps to modern .NET — async, DI, EF Core Code First, Polly v8, health checks, Serilog, and the Strangler Fig pattern. Companion repo for the article.

A multi-agent pipeline — Specifier, Coder, Refactorer, Architect — that turns informal requirements into mutation-tested, property-verified .NET code. Companion repo for the article.

Two-tier caching with built-in stampede protection and tag invalidation, replacing the IMemoryCache/IDistributedCache split with one API. Companion repo for the article.