Remove ExperimentalAttribute from official Extensions/Tasks/MRTR APIs and align MCPEXP001 usage (#1642)

docs/list-of-diagnostics.md

@@ -27,7 +27,7 @@ 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` | Experimental APIs tied to MCP specification features. Reuse this ID for newly introduced experimental spec features, and add feature-specific messages/URLs in `Experimentals`. |
 | `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). |
 | `MCPEXP003` | Experimental MCP Apps extension APIs. MCP Apps is the first official MCP extension (`io.modelcontextprotocol/ui`), enabling servers to deliver interactive UIs inside AI clients (see [MCP Apps specification](https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/2026-01-26/apps.mdx)). |
 

src/Common/Experimentals.cs

@@ -9,8 +9,8 @@ namespace ModelContextProtocol;
 /// Experimental diagnostic IDs are grouped by category:
 /// <list type="bullet">
 /// <item><description>
-/// <c>MCPEXP001</c> covers APIs related to experimental features in the MCP specification itself,
-/// such as Extensions. These APIs may change as the specification evolves.
+/// <c>MCPEXP001</c> covers APIs related to experimental features in the MCP specification itself.
+/// These APIs may change as the specification evolves.
 /// </description></item>
 /// <item><description>
 /// <c>MCPEXP002</c> covers experimental SDK APIs that are unrelated to the MCP specification,
@@ -36,19 +36,13 @@ namespace ModelContextProtocol;
 internal static class Experimentals
 {
     /// <summary>
-    /// Diagnostic ID for the experimental MCP Extensions feature.
+    /// Diagnostic ID for experimental MCP specification features.
     /// </summary>
-    public const string Extensions_DiagnosticId = "MCPEXP001";
-
-    /// <summary>
-    /// Message for the experimental MCP Extensions feature.
-    /// </summary>
-    public const string Extensions_Message = "The Extensions feature is part of a future MCP specification version that has not yet been ratified and is subject to change.";
-
-    /// <summary>
-    /// URL for the experimental MCP Extensions feature.
-    /// </summary>
-    public const string Extensions_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#mcpexp001";
+    /// <remarks>
+    /// When introducing a new experimental specification feature, add feature-specific message
+    /// and URL constants that use this diagnostic ID.
+    /// </remarks>
+    public const string SpecificationFeature_DiagnosticId = "MCPEXP001";
 
     /// <summary>
     /// Diagnostic ID for experimental MCP Apps extension APIs.
@@ -110,22 +104,4 @@ internal static class Experimentals
     /// </summary>
     public const string RunSessionHandler_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#mcpexp002";
 
-    /// <summary>
-    /// Diagnostic ID for the experimental Multi Round-Trip Requests (MRTR) feature.
-    /// </summary>
-    /// <remarks>
-    /// This uses the same diagnostic ID as <see cref="Extensions_DiagnosticId"/> because MRTR
-    /// is an experimental feature in the MCP specification (SEP-2322).
-    /// </remarks>
-    public const string Mrtr_DiagnosticId = "MCPEXP001";
-
-    /// <summary>
-    /// Message for the experimental MRTR feature.
-    /// </summary>
-    public const string Mrtr_Message = "The Multi Round-Trip Requests (MRTR) feature is experimental per the MCP specification (SEP-2322) and is subject to change.";
-
-    /// <summary>
-    /// URL for the experimental MRTR feature.
-    /// </summary>
-    public const string Mrtr_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#mcpexp001";
 }

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;
@@ -84,7 +83,6 @@ 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
     {

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
 {

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>

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>

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
 {

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 @@ public abstract class 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 abstract class RequestParams
     /// exact value without modification.
     /// </para>
     /// </remarks>
-    [Experimental(Experimentals.Mrtr_DiagnosticId, UrlFormat = Experimentals.Mrtr_Url)]
     [JsonIgnore]
     public string? RequestState
     {

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;
 
@@ -82,7 +81,6 @@ 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
     {

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>

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();

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>

src/ModelContextProtocol.Core/Server/McpServer.Methods.cs

@@ -600,7 +600,6 @@ public abstract partial class McpServer : McpSession
     /// <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)

src/ModelContextProtocol.Core/Server/McpServer.cs

@@ -81,7 +81,6 @@ public abstract partial class McpServer : McpSession
     /// 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>

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();

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,