What's new in ASP.NET Core in .NET 11 Preview 6

[Copilot]

Adds Preview 6 content to the cumulative "What's new in ASP.NET Core in .NET 11" article, generated from the dotnet/core release notes (dotnet/core#10456) via the whats-new-from-release-notes agent.

Note on parameters: The issue body listed PREVIEW = preview5, but the referenced source PR and the issue title are both Preview 6. Processed Preview 6 accordingly.

New include files

• Minimal APIs — async-validation-minimal-apis-preview-6.md (IAsyncValidatableObject, AsyncValidationAttribute, Validator.ValidateObjectAsync), short-circuit-endpoints-attribute-preview-6.md ([ShortCircuit])
• OpenAPI — openapi-3-2-default-preview-6.md (documents now target 3.2 by default)
• SignalR — signalr-authentication-refresh-preview-6.md (token refresh without reconnect), signalr-cancel-hub-invocations-preview-6.md (client-side cancellation of non-streaming invocations)

Updated files

• csharp-unions-preview-6.md — expanded to reflect the grown source: unions now span Minimal APIs, MVC/Razor Pages, SignalR JSON hub protocol, and Blazor, plus OpenAPI anyOf schema behavior and non-body binding limits.
• aspnetcore-11.md — added [!INCLUDE] directives in the mapped sections; bumped ms.date to 07/10/2026; Breaking changes section left intact.

Excluded (per content rules)

• Blazor Virtualize scroll-to-item — owned by the Blazor docs team; flagged, not authored here.
• Bug fixes and the standalone contributors list — inline contributor thank-yous (@Youssef1313, @Porozhniakov) are preserved within their feature includes.

Conventions

Includes use H3 headings, no front matter, -preview-6 suffixes, relative Learn links, and present-tense phrasing. Verified <xref:> IDs are used where docs exist; brand-new Preview 6 APIs without published docs carry <!-- TODO: Update to <xref:> ... --> markers for later conversion.

---

Internal previews

📄 File	🔗 Preview link
aspnetcore/release-notes/aspnetcore-11.md	aspnetcore/release-notes/aspnetcore-11

[wadepickett]

@tdykstra and @guardrex,
I started a draft for this. There may be udpates of the release notes to sync with between now and the final version. This does not include any update related to Blazor yet @guardrex since you usually like to do you own, but you can add to this draft if you want. As a reminder I am not available all next week. Tdykstra will take this over from here for any sync.

[guardrex]

@wadepickett ... Thanks!👍 Illona has a PR up, and I have one with only the Blazor C# union bits on it. I'll check next week to see what else Blazor needs. I'll review this Monday morning (without commits from me) to assist @tdykstra with the approval he'll need.

[guardrex]

Approving with a handful of NIT suggestions.

[guardrex]

@tdykstra ... I left a few suggestions earlier and a date update for the main What's New article. I'll go ahead and see if it will let me commit them. This PR should be merged after mine because we want the Blazor What's New INCLUDES file pulled into the build here. I can't merge mine yet ... I need a sign-off on it.

UPDATE: Yes, I was able to commit the changes. We need my PR reviewed/merged first, and then this one ... and then merge to live if there's nothing else.

[guardrex]

BTW, the CSRF middleware should probably be added to the Built-in middleware table at ...

https://learn.microsoft.com/en-us/aspnet/core/fundamentals/middleware/?view=aspnetcore-10.0#built-in-middleware