Consider Evaluating Experimental Types as Part of Back Compat Handling #12132

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1. Jorge Rangel (jorgerangel-msft)

   added

   emitter:client:csharpIssue for the C# client emitter: @typespec/http-client-csharpIssue for the C# client emitter: @typespec/http-client-csharp

   on Oct 7, 2026
2. github-actions

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   featureNew feature or requestNew feature or request

   on Oct 7, 2026
3. github-actions commented on Oct 7, 2026

   

   github-actionsBot

   on Oct 7, 2026 – with GitHub Actions

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   🎯 Issue Triage
   This requests that C# client-emitter compatibility processing recognize experimental types and avoid preserving their prior contracts across releases.
   Category: Feature Request
   Area: emitter:client:csharp

   🔍 Analysis

   The affected component is the C# client emitter's ApiCompatVersion/last-contract handling. The compatibility pass currently applies preserved API details without consulting experimental metadata, so intentionally unstable types may receive compatibility transformations that conflict with their current shape. #12133 is related: it reports obsolete enum serialization being preserved after an experimental type changes to an extensible enum, but it is a concrete bug rather than a duplicate of this broader policy request.

   📝 Suggested next steps

   • Define whether experimental status in either the baseline, current contract, or both should suppress compatibility handling.
   • Add compatibility tests covering types entering, leaving, and remaining experimental between releases.
   • Verify that suppression applies consistently to models, enums/unions, properties, and generated serialization.

   Generated by Agentic Triage
4. Jorge Rangel (jorgerangel-msft)

   assigned

   Copilot

   and

   Jorge Rangel (jorgerangel-msft)

   on Oct 12, 2026
5. Copilot

   linked a pull request that will close this issueSkip C# back compatibility for previously released experimental types #12159on Oct 12, 2026
6. Jorge Rangel (jorgerangel-msft)

   closed this as completedin #12159on Oct 15, 2026
7. H Nazmul Hassan (Naz-Ovh)

   added a commit that references this issue on Oct 15, 2026

   Skip C# back compatibility for previously released experimental types (…

   ...

   This issue will close once commit 57c3a22 is merged into the 'main' branch.

   57c3a22