.NETPro #37: Outdated .NET Best Practices, .NET 11 Preview 5, C# Union Types, MCP Server Templates, Build 2026 Highlights, and More...
🌏 Actionable .NET tips, the latest updates, and community insights, all in one place
Union types in C#, one of the most requested language features ever, are finally here. And that is just one of the things .NET 11 Preview 5 brings to the table. Alongside union types, this preview delivers native LINQ outer joins, a built-in MCP Server template, and a handful of other updates that feel like the platform is really hitting its stride. I’ve gone through everything and pulled out what actually matters for your day-to-day work.
Build 2026 sessions are now available on demand, and I’ve featured two of the event’s most-watched talks to help you catch up on the highlights. If you’re reading this before 4 PM UTC today, there’s also still time to tune in to the .NET Day on Agentic Modernization livestream.
My favorite part of this issue? Two standout video picks. Milan Jovanović explores the Inbox Pattern and its role in building reliable messaging systems, while Nick Chapsas revisits several long-standing .NET best practices that may no longer deserve a place in your codebase.
Here’s a quick look at today’s highlights:
➡️ .NET Day on Agentic Modernization goes live today at 4 PM UTC
➡️ .NET 11 Preview 5 is out
➡️ Must-watch .NET sessions at Microsoft Build 2026
➡️ .NET and .NET Framework June 2026 servicing releases updates
➡️ Build for the agentic web with .NET 11
➡️ The Inbox Pattern in .NET (the Outbox’s missing half)
➡️ Some .NET best practices worth rethinking
➡️ .NET 11 in depth: Runtime, libraries, and SDK for the AI era
Keep reading, and when you’re done, drop us a note about what you enjoyed and how we can make the next edition more helpful.
Cheers!
Adrija Mitra
Editor-in-Chief
✈️ .NET 11 Preview 5 is here and it’s a good one!
.NET 11 Preview 5 just dropped, and there’s a lot to be excited about across the whole stack. Here are the updates worth your attention:
➡️ C# gets some exciting new language features. Union declarations and closed class hierarchies are landing. This is the kind of type-system expressiveness that C# developers have been asking for. If you write a lot of domain modeling code, this is going to feel great.
➡️ The SDK is getting smarter about developer experience. Two wins here: file-based apps can now reference other C# files (great for scripting and lightweight tooling), and there’s now a built-in MCP Server template via dotnet new, a clear signal of where the AI integration story is heading.
➡️ Libraries are filling real gaps. LINQ now supports full outer joins natively (finally!), and System.Text.Json gets JSON Lines support, perfect for streaming data scenarios.
➡️ The runtime keeps getting faster. Runtime-async suspension improvements and GC trimming and compaction work mean your async-heavy workloads and memory footprint both benefit, no code changes needed.
➡️ Blazor is closing its gaps. SSR now supports client-side validation, and QuickGrid works without interactivity, both quality-of-life fixes that make the full-stack Blazor story much more practical.
➡️ EF Core gets a welcome safety net. The new EF1004 analyzer warning catches async EF queries running synchronously, a subtle but nasty performance bug that now gets flagged at build time rather than in production.
Give this preview a spin with the .NET 11 Preview 5 SDK, and let us know what you think!
📰 What’s Happening in .NET: More Highlights
The latest .NET breakthroughs are here. Haven’t explored them yet? Dive in now!
➡️ .NET at Microsoft Build 2026: Must watch sessions: Microsoft Build 2026 was packed with exciting .NET updates! The biggest buzz? Union types are finally coming to C#, one of the most requested language features ever, bringing elegant domain modeling to the language. There's also a strong AI push, with sessions on AI building blocks for C# apps and building for the agentic web with ASP.NET Core and Blazor. And mobile devs will love seeing on-device AI land in .NET MAUI. Missed it live? The full playlist is on YouTube and ready to binge!
➡️ .NET and .NET Framework June 2026 servicing releases updates: The June 9, 2026 Patch Tuesday drop is live, and it's a good one! This month’s update includes important CVE fixes, so security-conscious teams will definitely want to prioritize this one. .NET 10 (LTS), .NET 9, and .NET 8 all remain in active support, so make sure you’re running the latest patch on whichever version your stack targets. Update today and stay ahead of the curve!
⏱️ Don’t Miss It
.NET Day on Agentic Modernization goes live today at 4 PM UTC
June 16, 4:00–8:00 PM UTC
Microsoft Reactor is running a four-hour livestream focused on modernizing .NET apps with agentic tooling and AI, and it’s worth blocking your calendar for.
The agenda covers GitHub Copilot-assisted migration workflows, using Aspire to modernize without a full rewrite, and adding agentic capabilities via Microsoft Agent Framework and Foundry. There are also real-world sessions on WinForms and line-of-business app migrations, so it’s grounded in the kind of work most teams are actually doing rather than greenfield demos.
Before joining, watch the Build 2026 session Using AI tools to teach old apps new tricks on YouTube. It sets up the same themes the livestream will build on.
✒️ Got a Minute?
Tell us what you loved, what you want more of, and how we can make .NETPro even better in 2026. This quick 1-minute survey helps shape future issues around what matters most to you.
🧑🏼💻 What .NET Experts Are Talking About
Inside the minds of .NET pros: Real-world experience, real insights!
➡️ The Inbox Pattern in .NET (The Outbox’s Missing Half): Most message brokers guarantee at-least-once delivery, not exactly-once delivery. That means your consumers will see duplicate messages, and if your handlers are not prepared for that, you can end up with corrupted side effects.
In this video, Milan Jovanović walks you through the Inbox Pattern, the consumer-side counterpart to the Outbox Pattern, and shows how to buffer incoming messages, enforce idempotency using a unique constraint and ON CONFLICT DO NOTHING, and build a background processor that safely drains the inbox.
Business logic remains outside the inbox transaction, and you’ll see exactly why that boundary matters.
➡️ Best Practices in .NET I Don’t Like Anymore: Opinions change. After seven years of building .NET software, Nick Chapsas has quietly moved away from practices he once championed. Clean architecture, unit testing pyramids, AutoMapper, MediatR, and repository patterns over EF Core all get a second look here. Not a takedown, but an honest account of what stopped making sense as codebases grew and agentic workflows entered the picture. Worth watching if your stack still looks like it did in 2018.
➡️ Building for the agentic web with .NET 11: In this session, Daniel Roth explores how .NET 11 is evolving to meet the demands of modern, cloud-native, and AI-powered experiences through enhanced performance, security, observability, and developer productivity. From Blazor and Minimal APIs to Aspire integration and agentic application development, the presentation highlights the tools, frameworks, and innovations that position .NET as a leading platform for building future-ready web applications.
➡️ .NET 11 in depth: Runtime, libraries, and SDK for the AI era: This deep dive into .NET 11 runtime, libraries, and SDK is a rewarding watch for any .NET dev. Richard Lander and Chet Husk bring real technical depth while keeping things accessible and energetic. From native AOT CLI improvements and agent-aware tooling to revamped process APIs and runtime performance gains, the session makes clear that .NET 11 is a thoughtfully engineered release built for the demands of the AI era.
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And That’s a Wrap 🎬
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