What's new in ASP.NET Core in .NET 11 Preview 5

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: 05/19/2026
+ms.date: 06/09/2026
 uid: aspnetcore-11
 ---
 # What's new in ASP.NET Core in .NET 11
@@ -48,6 +48,8 @@ This section describes new features for OpenAPI.
 
 [!INCLUDE[](~/release-notes/aspnetcore-11/includes/file-result-openapi-preview4.md)]
 
+[!INCLUDE[](~/release-notes/aspnetcore-11/includes/openapi-schema-improvements-preview-5.md)]
+
 ## Authentication and authorization
 
 This section describes new features for authentication and authorization.
@@ -82,6 +84,8 @@ This section describes miscellaneous new features in .NET 11.
 
 [!INCLUDE[](~/release-notes/aspnetcore-11/includes/rate-limiting-retry-after-preview-4.md)]
 
+[!INCLUDE[](~/release-notes/aspnetcore-11/includes/kestrel-trailer-header-timeouts-preview-5.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/kestrel-trailer-header-timeouts-preview-5.md

@@ -0,0 +1,10 @@
+### Kestrel applies trailer header timeouts
+
+Kestrel now applies <xref:Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServerLimits.RequestHeadersTimeout> to fragmented HTTP/2 and HTTP/3 trailer headers that don't finish sending the header block. The same timeout that protects initial request headers now also prevents connections from staying open indefinitely while Kestrel waits for trailer `HEADERS` frames to complete.
+
+```csharp
+builder.WebHost.ConfigureKestrel(options =>
+{
+    options.Limits.RequestHeadersTimeout = TimeSpan.FromSeconds(10);
+});
+```

aspnetcore/release-notes/aspnetcore-11/includes/openapi-schema-improvements-preview-5.md

@@ -0,0 +1,21 @@
+### OpenAPI schemas better match ASP.NET Core behavior
+
+OpenAPI generation now handles several schema cases more accurately. Non-body enum parameters keep the original C# enum member names even when HTTP JSON options configure a <xref:System.Text.Json.Serialization.JsonStringEnumConverter> naming policy, because query, route, header, and form binding use `Enum.TryParse` rather than JSON serialization. Array schema reference IDs now use valid component names such as `stringArray` and `TodoArray` instead of names with array syntax.
+
+```csharp
+builder.Services.ConfigureHttpJsonOptions(options =>
+{
+    options.SerializerOptions.Converters.Add(
+        new JsonStringEnumConverter(JsonNamingPolicy.KebabCaseLower));
+});
+
+app.MapGet("/orders", (OrderStatus status) => Results.Ok(status));
+```
+
+With this configuration, a body schema can still describe `OrderStatus.PendingReview` as `pending-review`, while the query parameter schema describes the accepted value as `PendingReview`.
+
+Minimal API endpoints can support multiple <xref:Microsoft.AspNetCore.Http.OpenApiRouteHandlerBuilderExtensions.Produces%2A> extension method calls for the same status code—for example, to specify that a 200 response may arrive as `application/json` or `text/plain` with different schemas. The same support applies to MVC controllers via multiple [`[ProducesResponseType]`](xref:Microsoft.AspNetCore.Mvc.ProducesResponseTypeAttribute) attributes.
+
+In prior releases, the framework collapsed each status code to a single response type and silently dropped the rest, making it impossible to describe endpoints that serve multiple content types. <xref:Microsoft.AspNetCore.Mvc.ApiExplorer> now preserves every declared response type with deterministic ordering, and the generated OpenAPI document emits separate content entries per media type—or an `anyOf` schema when multiple types share the same content type.
+
+Thank you [@marcominerva](https://github.com/marcominerva) for the array schema reference contribution!