F# Weekly #20, 2026 – .NET 11 Preview 4 and SwaggerProvider 4.0

Welcome to F# Weekly,

A roundup of F# content from this past week:

News

• [System.Text.Json] now understands F# discriminated unions out of the box
• SwaggerProvider v4.0.0

"[System.Text.Json] now understands F# discriminated unions out of the box" github.com/dotnet/core/…

— Jon Sagara (@jonsagara.com) 2026-05-13T15:32:43.689Z

Microsoft News

• .NET 11 Preview 4 is now available!
• .NET and .NET Framework May 2026 servicing releases updates
• Process API Improvements in .NET 11
• .NET MAUI Moves to CoreCLR in .NET 11
• From beta to stable: Announcing the Azure SDK for Rust 🎉🦀 – Azure SDK Blog
• WebAssembly Data Processing at the Edge with Azure IoT Operations – ISE Developer Blog
• Visual Studio Code 1.120 with Agents window
• Agent Skills in Visual Studio: Teach Copilot How Your Team Works – Visual Studio Blog
• Introducing WinUI agent plugin for GitHub Copilot and Claude Code – #ifdef Windows

Videos

• Yapping about GUIs, F# and Lisp
• Blazor Community Standup: E2E Component Testing for Blazor

Blogs

• ragingHungryPanda: Shared Postgres Test Container with Expecto in F#
• brandewinder: Computing lighting and shadows of mountains from above in F#
• Event Sourcing: compensation – the simple way out when things go wrong – planetgeek.ch

Highlighted projects

• Azizs2162/fyper — Build type-safe Cypher queries in F# with plain records, query expressions, and automatic parameterization
• agentruntimecontrolprotocol/fsharp-sdk — F# / .NET reference SDK for ARCP (Agent Runtime Control Protocol) with durable execution and human-in-the-loop support
• MagnusOpera/FScript — Functional language interpreter inspired by F#/ML, with type inference and LSP support
• goswinr/Euclid — A 2D and 3D geometry library for F# (and JavaScript via Fable)
• elekvk/FocusQuest — Gamified productivity web app built with F#, Bolero and ASP.NET Core

New Releases

• FSharp.Data 8.1.14
• FSharp.Compiler.Service 43.12.204
• WebSharper 10.1.4.673
• Feliz 3.3.2
• Feliz.UseElmish 5.0.0
• Feliz.CompilerPlugins 3.2.0
• SwaggerProvider 4.0.0
• SageFs 0.6.273
• FSharp.Formatting 22.0.1
• fsdocs-tool 22.0.1
• RProvider 3.0.0
• FSharp.Idioms 1.5.10

SwaggerProvider v4.0.0 is live! 🎉 #fsharpOverhauled for speed, cleaner code gen, and better developer ergonomics.⚡ Blazing fast zero-allocation hot paths📅 Native DateOnly & TimeOnly support📝 Richer IDE docs via inline XmlDoc⚠️ Breaking: Legacy v2 compiler removedgithub.com/fsprojects/S…

— Sergey Tihon 🦔🦀 (@sergeytihon.com) 2026-05-16T18:26:10.183Z

That’s all for now. Have a great week.

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