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.

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Internal previews

📄 File	🔗 Preview link
aspnetcore/release-notes/aspnetcore-11.md	What's new in ASP.NET Core in .NET 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 tomorrow morning (without commits from me) to assist @tdykstra with the approval he'll need.