Add rate-limiting RetryAfter fixes to What's New for .NET 11 Preview 4 (#37151)

* Initial plan

* Add rate-limiting fixes include file for preview4

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* Add code sample from source release notes to rate-limiting include file

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* Apply suggestion from @wadepickett

Removing cross-link until <xref:System.Threading.RateLimiting.ChainedRateLimiter%601> is avaialble in API ref build.

* Update rate-limiting-retry-after-preview4.md

Removing code snippet per review suggestion. It is not relevant to the ASP.NET Core rate limiting middleware scenario.

* Rename include file to rate-limiting-retry-after-preview-4.md and update reference

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* Apply suggestion from @danroth27

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* Apply suggestion from @wadepickett

* Apply suggestion from @wadepickett

Fix per gewarren review suggestion.

---------

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Author: 3 people

aspnetcore/release-notes/aspnetcore-11.md

@@ -5,7 +5,7 @@ author: wadepickett
 description: Learn about the new features in ASP.NET Core in .NET 11.
 ms.author: wpickett
 ms.custom: mvc
-ms.date: 05/13/2026
+ms.date: 05/14/2026
 uid: aspnetcore-11
 ---
 # What's new in ASP.NET Core in .NET 11
@@ -80,6 +80,8 @@ This section describes miscellaneous new features in .NET 11.
 
 [!INCLUDE[](~/release-notes/aspnetcore-11/includes/runtime-async-shared-framework-preview4.md)]
 
+[!INCLUDE[](~/release-notes/aspnetcore-11/includes/rate-limiting-retry-after-preview-4.md)]
+
 ## Breaking changes
 
 Use the articles in [Breaking changes in .NET](/dotnet/core/compatibility/breaking-changes) to find breaking changes that might apply when upgrading an app to a newer version of .NET.

aspnetcore/release-notes/aspnetcore-11/includes/rate-limiting-retry-after-preview-4.md

@@ -0,0 +1,9 @@
+### Rate-limiting middleware returns accurate `Retry-After` headers
+
+The <xref:System.Threading.RateLimiting.FixedWindowRateLimiter> now reports a <xref:System.Threading.RateLimiting.MetadataName.RetryAfter> metadata value that accurately reflects the next window boundary. Apps that propagate this metadata to the `Retry-After` response header in their <xref:Microsoft.AspNetCore.RateLimiting.RateLimiterOptions.OnRejected> callback now produce correct retry intervals automatically, with no code changes required.
+
+Additional fixes in `System.Threading.RateLimiting` resolve an issue where <xref:System.Threading.RateLimiting.TokenBucketRateLimiter> mishandled partial token refills during zero-permit acquisition, and improve the chained rate limiter returned by <xref:System.Threading.RateLimiting.RateLimiter.CreateChained*> to correctly forward idle-duration and replenishment behavior from its inner limiters.
+
+For an overview of the rate limiting middleware, see [Rate limiting middleware in ASP.NET Core](/aspnet/core/performance/rate-limit).
+
+Thank you [@asbjornvad](https://github.com/asbjornvad) and [@apoorvdarshan](https://github.com/apoorvdarshan) for these contributions!