Remove experimental attributes from official APIs

Copilot · PranavSenthilnathan · web-flow · commit 645396192f80 · 2026-06-11T20:55:49.000Z
Co-authored-by: PranavSenthilnathan &lt;12225508+PranavSenthilnathan@users.noreply.github.com&gt;
diff --git a/docs/list-of-diagnostics.md b/docs/list-of-diagnostics.md
@@ -23,7 +23,7 @@ If you use experimental APIs, you will get one of the diagnostics shown below. T
 
 | Diagnostic ID | Description |
 | :------------ | :---------- |
-| `MCPEXP001` | Experimental APIs for features in the MCP specification itself, including Tasks and Extensions. Tasks provide a mechanism for asynchronous long-running operations that can be polled for status and results (see [SEP-2663](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/seps/2663-tasks-extension.md)). Extensions provide a framework for extending the Model Context Protocol while maintaining interoperability (see [SEP-2133](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2133)). |
+| `MCPEXP001` | Reserved diagnostic ID for APIs that were previously experimental and tied to MCP specification features (including Tasks, Extensions, and MRTR). This ID is intentionally kept and not reused for future diagnostics. |
 | `MCPEXP002` | Experimental SDK APIs unrelated to the MCP specification itself, including subclassing `McpClient`/`McpServer` (see [#1363](https://github.com/modelcontextprotocol/csharp-sdk/pull/1363)) and `RunSessionHandler`, which may be removed or change signatures in a future release (consider using `ConfigureSessionOptions` instead). |
 
 ## Obsolete APIs
diff --git a/src/ModelContextProtocol.Core/Protocol/ClientCapabilities.cs b/src/ModelContextProtocol.Core/Protocol/ClientCapabilities.cs
@@ -1,5 +1,4 @@
 using System.ComponentModel;
-using System.Diagnostics.CodeAnalysis;
 using System.Text.Json.Serialization;
 using ModelContextProtocol.Client;
 using ModelContextProtocol.Server;
@@ -82,7 +81,6 @@ public sealed class ClientCapabilities
     /// interoperability. Clients advertise extension support via this field during the initialization handshake.
     /// </para>
     /// </remarks>
-    [Experimental(Experimentals.Extensions_DiagnosticId, UrlFormat = Experimentals.Extensions_Url)]
     [JsonIgnore]
     public IDictionary<string, object>? Extensions
     {
diff --git a/src/ModelContextProtocol.Core/Protocol/InputRequest.cs b/src/ModelContextProtocol.Core/Protocol/InputRequest.cs
@@ -1,4 +1,3 @@
-using System.Diagnostics.CodeAnalysis;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 
@@ -20,7 +19,6 @@ namespace ModelContextProtocol.Protocol;
 /// parameters can be accessed via the typed accessor properties.
 /// </para>
 /// </remarks>
-[Experimental(Experimentals.Mrtr_DiagnosticId, UrlFormat = Experimentals.Mrtr_Url)]
 [JsonConverter(typeof(Converter))]
 public sealed class InputRequest
 {
diff --git a/src/ModelContextProtocol.Core/Protocol/InputRequiredException.cs b/src/ModelContextProtocol.Core/Protocol/InputRequiredException.cs
@@ -1,5 +1,3 @@
-using System.Diagnostics.CodeAnalysis;
-
 namespace ModelContextProtocol.Protocol;
 
 /// <summary>
@@ -54,7 +52,6 @@ namespace ModelContextProtocol.Protocol;
 /// }
 /// </code>
 /// </example>
-[Experimental(Experimentals.Mrtr_DiagnosticId, UrlFormat = Experimentals.Mrtr_Url)]
 public class InputRequiredException : Exception
 {
     /// <summary>
diff --git a/src/ModelContextProtocol.Core/Protocol/InputRequiredResult.cs b/src/ModelContextProtocol.Core/Protocol/InputRequiredResult.cs
@@ -1,4 +1,3 @@
-using System.Diagnostics.CodeAnalysis;
 using System.Text.Json.Serialization;
 
 namespace ModelContextProtocol.Protocol;
@@ -22,7 +21,6 @@ namespace ModelContextProtocol.Protocol;
 /// This type is part of the Multi Round-Trip Requests (MRTR) mechanism defined in SEP-2322.
 /// </para>
 /// </remarks>
-[Experimental(Experimentals.Mrtr_DiagnosticId, UrlFormat = Experimentals.Mrtr_Url)]
 public sealed class InputRequiredResult : Result
 {
     /// <summary>
diff --git a/src/ModelContextProtocol.Core/Protocol/InputResponse.cs b/src/ModelContextProtocol.Core/Protocol/InputResponse.cs
@@ -1,4 +1,3 @@
-using System.Diagnostics.CodeAnalysis;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 using System.Text.Json.Serialization.Metadata;
@@ -21,7 +20,6 @@ namespace ModelContextProtocol.Protocol;
 /// the corresponding <see cref="InputRequest.Method"/> key in the <see cref="InputRequiredResult.InputRequests"/> map.
 /// </para>
 /// </remarks>
-[Experimental(Experimentals.Mrtr_DiagnosticId, UrlFormat = Experimentals.Mrtr_Url)]
 [JsonConverter(typeof(Converter))]
 public sealed class InputResponse
 {
diff --git a/src/ModelContextProtocol.Core/Protocol/RequestParams.cs b/src/ModelContextProtocol.Core/Protocol/RequestParams.cs
@@ -1,4 +1,3 @@
-using System.Diagnostics.CodeAnalysis;
 using System.Text.Json.Nodes;
 using System.Text.Json.Serialization;
 
@@ -36,7 +35,6 @@ private protected RequestParams()
     /// the value is the client's response to that input request.
     /// </para>
     /// </remarks>
-    [Experimental(Experimentals.Mrtr_DiagnosticId, UrlFormat = Experimentals.Mrtr_Url)]
     [JsonIgnore]
     public IDictionary<string, InputResponse>? InputResponses
     {
@@ -59,7 +57,6 @@ public IDictionary<string, InputResponse>? InputResponses
     /// exact value without modification.
     /// </para>
     /// </remarks>
-    [Experimental(Experimentals.Mrtr_DiagnosticId, UrlFormat = Experimentals.Mrtr_Url)]
     [JsonIgnore]
     public string? RequestState
     {
diff --git a/src/ModelContextProtocol.Core/Protocol/ServerCapabilities.cs b/src/ModelContextProtocol.Core/Protocol/ServerCapabilities.cs
@@ -1,5 +1,4 @@
 using System.ComponentModel;
-using System.Diagnostics.CodeAnalysis;
 using System.Text.Json.Serialization;
 using ModelContextProtocol.Server;
 
@@ -81,7 +80,6 @@ public sealed class ServerCapabilities
     /// interoperability. Servers advertise extension support via this field during the initialization handshake.
     /// </para>
     /// </remarks>
-    [Experimental(Experimentals.Extensions_DiagnosticId, UrlFormat = Experimentals.Extensions_Url)]
     [JsonIgnore]
     public IDictionary<string, object>? Extensions
     {
diff --git a/src/ModelContextProtocol.Core/Server/IMcpTaskStore.cs b/src/ModelContextProtocol.Core/Server/IMcpTaskStore.cs
@@ -1,5 +1,4 @@
 using ModelContextProtocol.Protocol;
-using System.Diagnostics.CodeAnalysis;
 using System.Text.Json;
 
 namespace ModelContextProtocol.Server;
@@ -31,7 +30,6 @@ namespace ModelContextProtocol.Server;
 /// specification for details on the tasks extension.
 /// </para>
 /// </remarks>
-[Experimental(Experimentals.Extensions_DiagnosticId, UrlFormat = Experimentals.Extensions_Url)]
 public interface IMcpTaskStore
 {
     /// <summary>
diff --git a/src/ModelContextProtocol.Core/Server/InMemoryMcpTaskStore.cs b/src/ModelContextProtocol.Core/Server/InMemoryMcpTaskStore.cs
@@ -1,7 +1,6 @@
 using ModelContextProtocol.Protocol;
 using System.Collections.Concurrent;
 using System.Collections.Immutable;
-using System.Diagnostics.CodeAnalysis;
 using System.Text.Json;
 
 namespace ModelContextProtocol.Server;
@@ -20,7 +19,6 @@ namespace ModelContextProtocol.Server;
 /// implement a custom <see cref="IMcpTaskStore"/>.
 /// </para>
 /// </remarks>
-[Experimental(Experimentals.Extensions_DiagnosticId, UrlFormat = Experimentals.Extensions_Url)]
 public class InMemoryMcpTaskStore : IMcpTaskStore
 {
     private readonly ConcurrentDictionary<string, McpTaskInfo> _tasks = new();
diff --git a/src/ModelContextProtocol.Core/Server/InputResponseReceivedEventArgs.cs b/src/ModelContextProtocol.Core/Server/InputResponseReceivedEventArgs.cs
@@ -1,12 +1,10 @@
 using ModelContextProtocol.Protocol;
-using System.Diagnostics.CodeAnalysis;
 
 namespace ModelContextProtocol.Server;
 
 /// <summary>
 /// Provides data for the <see cref="IMcpTaskStore.InputResponseReceived"/> event.
 /// </summary>
-[Experimental(Experimentals.Extensions_DiagnosticId, UrlFormat = Experimentals.Extensions_Url)]
 public sealed class InputResponseReceivedEventArgs
 {
     /// <summary>
diff --git a/src/ModelContextProtocol.Core/Server/McpServer.Methods.cs b/src/ModelContextProtocol.Core/Server/McpServer.Methods.cs
@@ -595,7 +595,6 @@ private void ThrowIfRootsUnsupported()
     /// <param name="taskId">The task ID in the store.</param>
     /// <param name="store">The task store to write input requests to.</param>
     /// <returns>An <see cref="IDisposable"/> that restores the previous context when disposed.</returns>
-    [Experimental(Experimentals.Extensions_DiagnosticId, UrlFormat = Experimentals.Extensions_Url)]
     public IDisposable CreateMcpTaskScope(
         string taskId,
         IMcpTaskStore store)
diff --git a/src/ModelContextProtocol.Core/Server/McpServer.cs b/src/ModelContextProtocol.Core/Server/McpServer.cs
@@ -80,7 +80,6 @@ protected McpServer()
     /// the required feature) instead of throwing <see cref="Protocol.InputRequiredException"/>.
     /// </para>
     /// </remarks>
-    [Experimental(Experimentals.Mrtr_DiagnosticId, UrlFormat = Experimentals.Mrtr_Url)]
     public virtual bool IsMrtrSupported => false;
 
     /// <summary>
diff --git a/src/ModelContextProtocol.Core/Server/McpTaskExecutionContext.cs b/src/ModelContextProtocol.Core/Server/McpTaskExecutionContext.cs
@@ -1,5 +1,3 @@
-using System.Diagnostics.CodeAnalysis;
-
 namespace ModelContextProtocol.Server;
 
 /// <summary>
@@ -9,7 +7,6 @@ namespace ModelContextProtocol.Server;
 /// and <see cref="McpServer.RequestRootsAsync(ModelContextProtocol.Protocol.ListRootsRequestParams, CancellationToken)"/>
 /// are redirected through the task store as input requests rather than sent directly to the client.
 /// </summary>
-[Experimental(Experimentals.Extensions_DiagnosticId, UrlFormat = Experimentals.Extensions_Url)]
 internal sealed class McpTaskExecutionContext
 {
     internal static readonly AsyncLocal<McpTaskExecutionContext?> Current = new();
diff --git a/src/ModelContextProtocol.Core/Server/McpTaskInfo.cs b/src/ModelContextProtocol.Core/Server/McpTaskInfo.cs
@@ -1,5 +1,4 @@
 using ModelContextProtocol.Protocol;
-using System.Diagnostics.CodeAnalysis;
 using System.Text.Json;
 
 namespace ModelContextProtocol.Server;
@@ -14,7 +13,6 @@ namespace ModelContextProtocol.Server;
 /// types (<see cref="CreateTaskResult"/>, <see cref="GetTaskResult"/>) when communicating with clients.
 /// </para>
 /// </remarks>
-[Experimental(Experimentals.Extensions_DiagnosticId, UrlFormat = Experimentals.Extensions_Url)]
 public sealed record McpTaskInfo(
     string TaskId,
     McpTaskStatus Status,
diff --git a/tests/ModelContextProtocol.Tests/ExperimentalInternalPropertyTests.cs b/tests/ModelContextProtocol.Tests/ExperimentalInternalPropertyTests.cs
@@ -1,5 +1,6 @@
 using System.Reflection;
 using System.Text.Json.Serialization;
+using ModelContextProtocol.Server;
 using ModelContextProtocol.Protocol;
 
 namespace ModelContextProtocol.Tests;
@@ -15,6 +16,29 @@ namespace ModelContextProtocol.Tests;
 /// </remarks>
 public class ExperimentalInternalPropertyTests
 {
+    [Fact]
+    public void OfficialExtensionsTasksAndMrtrApis_AreNotExperimental()
+    {
+        static bool HasExperimentalAttribute(ICustomAttributeProvider provider) =>
+            provider.GetCustomAttributes(inherit: false).Any(a => a.GetType().Name == "ExperimentalAttribute");
+
+        Assert.False(HasExperimentalAttribute(typeof(InputRequest)));
+        Assert.False(HasExperimentalAttribute(typeof(InputResponse)));
+        Assert.False(HasExperimentalAttribute(typeof(InputRequiredResult)));
+        Assert.False(HasExperimentalAttribute(typeof(InputRequiredException)));
+        Assert.False(HasExperimentalAttribute(typeof(IMcpTaskStore)));
+        Assert.False(HasExperimentalAttribute(typeof(InMemoryMcpTaskStore)));
+        Assert.False(HasExperimentalAttribute(typeof(InputResponseReceivedEventArgs)));
+        Assert.False(HasExperimentalAttribute(typeof(McpTaskInfo)));
+
+        Assert.False(HasExperimentalAttribute(typeof(ClientCapabilities).GetProperty(nameof(ClientCapabilities.Extensions))!));
+        Assert.False(HasExperimentalAttribute(typeof(ServerCapabilities).GetProperty(nameof(ServerCapabilities.Extensions))!));
+        Assert.False(HasExperimentalAttribute(typeof(RequestParams).GetProperty(nameof(RequestParams.InputResponses))!));
+        Assert.False(HasExperimentalAttribute(typeof(RequestParams).GetProperty(nameof(RequestParams.RequestState))!));
+        Assert.False(HasExperimentalAttribute(typeof(McpServer).GetProperty(nameof(McpServer.IsMrtrSupported))!));
+        Assert.False(HasExperimentalAttribute(typeof(McpServer).GetMethod(nameof(McpServer.CreateMcpTaskScope))!));
+    }
+
     [Fact]
     public void ExperimentalProperties_MustBeHiddenFromSourceGenerator()
     {
