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.NET 11 RC - AOT Mode - System.NotSupportedException: ElementType is not initialized when `Microsoft.AspNetCore.Mvc.ApiExplorer.IsEnhancedModelMetadataSupported` is false.

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@commonsensesoftware is already working on this.

Since Sep 19, 2026.

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Description

bug triage
Is there an existing issue for this?
  • I have searched the existing issues
Describe the bug

With <PublishAot>true</PublishAot> in the project (even under dotnet run), requesting a versioned OpenAPI doc throws.

Image

Commenting out PublishAot in *.csproj fixes it. Reproduces with both DateOnly-based and integer ApiVersions, so unrelated to versioning scheme.

Expected Behavior

Asp.Versioning.OpenApi 10.2.3 itself declares IsAotCompatible: True / IsTrimmable: True in its assembly metadata which means AOT mode is supported. The package should succeed in generating OpenAPI JSON document with .NET 11 SDK.

Steps To Reproduce
> dotnet --info  # 11.0.100-rc.1
> dotnet new webapiaot -n api-explorer
> cd api-explorer
> dotnet add package Asp.Versioning.OpenApi  # 10.2.3
> dotnet add package Scalar.AspNetCore
  • Edit Program.cs and add code to version minimal API
...
builder.Services.AddApiVersioning(options =>
    {
        options.ApiVersionReader = new HeaderApiVersionReader("X-Product-Version");
        options.ReportApiVersions = true;
    })
    .AddApiExplorer(options => {
        options.GroupNameFormat = "'v'yyy-MM";
    })
    .AddOpenApi(options =>
    {
        options.Document.AddScalarTransformers();
    });

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.MapOpenApi().WithDocumentPerVersion();
    app.MapScalarApiReference(options =>
    {

        var descriptions = app.DescribeApiVersions();

        for ( var i = 0; i < descriptions.Count; i++ )
        {
            var description = descriptions[i];
            var isDefault = i == descriptions.Count - 1;

            options.AddDocument( description.GroupName, description.GroupName, isDefault: isDefault );
        }
    });
}

Todo[] sampleTodos =
[
    new(1, "Walk the dog"),
    new(2, "Do the dishes", DateOnly.FromDateTime(DateTime.Now)),
    new(3, "Do the laundry", DateOnly.FromDateTime(DateTime.Now.AddDays(1))),
    new(4, "Clean the bathroom"),
    new(5, "Clean the car", DateOnly.FromDateTime(DateTime.Now.AddDays(2)))
];

var versionSet = app.NewApiVersionSet("Product")
.HasDeprecatedApiVersion(new ApiVersion(new DateOnly(2026,8,1)))
.HasApiVersion(new ApiVersion(new DateOnly(2026,9,1)))
.ReportApiVersions()
.Build();

var todosApi = app.MapGroup("/todos").WithApiVersionSet(versionSet);
todosApi.MapGet("/", () => sampleTodos)
        .WithName("GetTodos");

todosApi.MapGet("/{id}", Results<Ok<Todo>, NotFound> (int id) =>
    sampleTodos.FirstOrDefault(a => a.Id == id) is { } todo
        ? TypedResults.Ok(todo)
        : TypedResults.NotFound())
    .WithName("GetTodoById").MapToApiVersion(new ApiVersion(new DateOnly(2026,8,1)));

app.Run();
Exceptions (if any)
System.NotSupportedException: ElementType is not initialized when `Microsoft.AspNetCore.Mvc.ApiExplorer.IsEnhancedModelMetadataSupported` is false.
   at Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata.get_ElementType()
   at Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.DefaultModelMetadata.get_ElementMetadata()
   at Asp.Versioning.ApiExplorer.VersionedModelMetadataProvider.Describe(ModelMetadata metadata, Type type, ApiVersion apiVersion, Boolean minimalApi)
   at Asp.Versioning.ApiExplorer.VersionedModelMetadataProvider.OnProvidersExecuted(ApiDescriptionProviderContext context)
   at Microsoft.AspNetCore.Mvc.ApiExplorer.ApiDescriptionGroupCollectionProvider.GetCollection(ActionDescriptorCollection actionDescriptors)
   at Microsoft.AspNetCore.Mvc.ApiExplorer.ApiDescriptionGroupCollectionProvider.get_ApiDescriptionGroups()
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetOpenApiPathsAsync(OpenApiDocument document, IServiceProvider scopedServiceProvider, IOpenApiOperationTransformer[] operationTransformers, IOpenApiSchemaTransformer[] schemaTransformers, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetOpenApiDocumentAsync(IServiceProvider scopedServiceProvider, HttpRequest httpRequest, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Builder.OpenApiEndpointRouteBuilderExtensions.<>c__DisplayClass0_0.<<MapOpenApi>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Http.Generated.<GeneratedRouteBuilderExtensions_g>F2F695FFF0C57E2AC66C44A89193E354033830917758BE7A77025BFF91AF84311__GeneratedRouteBuilderExtensionsCore.<>c__DisplayClass2_0.<<MapGet0>g__RequestHandler|5>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)
.NET Version

11.0.100-rc.1

Anything else?

No response

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