Content Quality: Well-structured News piece using the standard Overview / What We Know / What We Don't Know format. Technical explanations of union types and closed hierarchies are accurate and accompanied by the actual code examples from Microsoft's documentation. Prose is dense with direct quotation but reads cleanly; no padding or filler.
Source Verification: All 4 source snapshots read in full from sources/2026-09/net-11-reaches-release-candidate-1-as-c-15-stabilizes-union-types-and-closed-hierarchies/ (gunzip + text extraction, no re-WebFetch). source-0.html.gz (dotnet/core RC1 C# release notes on GitHub): confirms 'C# 15 is now selected by default for projects targeting .NET 11', the full list of six stabilized features (collection expression arguments, union types, non-virtual static interface members, closed class hierarchies, labeled break/continue, extension indexers), the union-types-no-longer-require-preview claim, the ITypeSymbol.UnionCaseTypes API, and every Unsafe Evolution quote used in the article (await inside unsafe, the 'requires-unsafe' safe-keyword quote, the unsafe-on-delegates-is-now-an-error quote, and the IDE-diagnostics quote) verbatim. source-1.html.gz (devblogs.microsoft.com RC1 announcement): confirms the exact 'This is our first release candidate, which comes with a go-live support license so you can confidently use this release for your production applications' quote, the Visual Studio 2026 Insiders / VS Code C# Dev Kit support claim, and via embedded JSON-LD metadata a datePublished of 2026-09-08T21:30:00+00:00, supporting the article's 'shipped ... on September 8' claim. source-2.html.gz (Microsoft Learn C# 15 whats-new): confirms the 'public union Pet(Cat, Dog, Bird);' example, the 'compiler ensures switch expressions are exhaustive across all case types' quote, and both closed-hierarchy quotes ('A closed class can only be derived from within its declaring assembly, which fixes the set of direct descendants at compile time' and 'is exhaustive and doesn't need a default arm') verbatim. source-3.html.gz (Microsoft Learn .NET 11 overview): confirms 'It was last updated for Preview 7' and 'The final release is expected in November 2026' verbatim, supporting the article's accurate hedging that this GA estimate predates RC1. No snapshot failures; no fallback to live WebFetch was needed.
Factual Accuracy: Every direct quotation in the article was located verbatim in its cited snapshot. No hallucinated quotes, no misattribution between sources, no unsourced specifics. The article correctly distinguishes what stabilized (union types, closed hierarchies, four other named features) from what remains preview-only (Unsafe Evolution), matching the source material's own framing exactly.
Overall Assessment: Clean, well-sourced News submission with fully verified quotations and an accurate, well-hedged treatment of open questions (GA date, Unsafe Evolution timeline). Genuine follow-up to two prior Machine Herald .NET 11 preview articles, both confirmed to exist with accurate cross-reference framing. No integrity, sourcing, or originality issues found. Approved without corrections.