Obsolete Roots, Sampling, and Logging surface area per SEP-2577

Mark all public API surface for the Roots, Sampling, and Logging features as
[Obsolete] in line with SEP-2577. This covers protocol DTOs, capability
properties, method-name constants, convenience methods, handlers, builders,
filters, and the related sampling/roots helpers on the input request/response
types. There is no functional or wire behavior change; the features continue to
work exactly as before.

All three features share a single diagnostic ID (MCP9005) so consumers can opt
out with one suppression, while feature-specific messages keep the diagnostics
distinguishable. Documents the new diagnostic in docs/list-of-diagnostics.md and
suppresses MCP9005 where the SDK, tests, and samples exercise the deprecated
APIs internally.

Author: tarekgh

docs/concepts/logging/samples/Directory.Build.props

@@ -0,0 +1,9 @@
+<Project>
+  <Import Project="$([MSBuild]::GetPathOfFileAbove('Directory.Build.props', '$(MSBuildThisFileDirectory)..'))" />
+
+  <PropertyGroup>
+    <!-- Suppress the Logging obsoletion warning (SEP-2577) in the logging sample projects,
+         which demonstrate the deprecated logging feature that continues to work. -->
+    <NoWarn>$(NoWarn);MCP9005</NoWarn>
+  </PropertyGroup>
+</Project>

docs/list-of-diagnostics.md

@@ -38,3 +38,4 @@ When APIs are marked as obsolete, a diagnostic is emitted to warn users that the
 | `MCP9002` | Removed | The `AddXxxFilter` extension methods on `IMcpServerBuilder` (e.g., `AddListToolsFilter`, `AddCallToolFilter`, `AddIncomingMessageFilter`) were superseded by `WithRequestFilters()` and `WithMessageFilters()`. |
 | `MCP9003` | In place | The `RequestContext<TParams>(McpServer, JsonRpcRequest)` constructor is obsolete. Use the overload that accepts a `parameters` argument: `RequestContext<TParams>(McpServer, JsonRpcRequest, TParams)`. |
 | `MCP9004` | In place | <xref:ModelContextProtocol.AspNetCore.HttpServerTransportOptions.EnableLegacySse> opts into the legacy SSE transport which has no built-in HTTP-level backpressure. Use Streamable HTTP instead. See [Stateless — Legacy SSE transport](xref:stateless#legacy-sse-transport) for details. |
+| `MCP9005` | In place | The Roots, Sampling, and Logging features are deprecated as of specification version 2026-07-28 and may be removed in a future version. See SEP-2577 for more information. |

samples/Directory.Build.props

@@ -0,0 +1,9 @@
+<Project>
+  <Import Project="$([MSBuild]::GetPathOfFileAbove('Directory.Build.props', '$(MSBuildThisFileDirectory)..'))" />
+
+  <PropertyGroup>
+    <!-- Suppress the Roots, Sampling, and Logging obsoletion warning (SEP-2577) in sample projects
+         that demonstrate the deprecated features, which continue to work. -->
+    <NoWarn>$(NoWarn);MCP9005</NoWarn>
+  </PropertyGroup>
+</Project>

src/Common/Obsoletions.cs

@@ -33,4 +33,13 @@ internal static class Obsoletions
     public const string EnableLegacySse_DiagnosticId = "MCP9004";
     public const string EnableLegacySse_Message = "Legacy SSE transport has no built-in request backpressure and should only be used with completely trusted clients in isolated processes. Use Streamable HTTP instead.";
     public const string EnableLegacySse_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#obsolete-apis";
+
+    // SEP-2577 deprecates the Roots, Sampling, and Logging features as a single coordinated
+    // deprecation. They share one diagnostic ID (MCP9005) so consumers can opt out with a single
+    // suppression, while the feature-specific messages keep the diagnostics distinguishable.
+    public const string Deprecated_DiagnosticId = "MCP9005";
+    public const string Deprecated_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#mcp9005";
+    public const string DeprecatedRoots_Message = "The Roots feature is deprecated as of specification version 2026-07-28 and may be removed in a future version. See SEP-2577 for more information.";
+    public const string DeprecatedSampling_Message = "The Sampling feature is deprecated as of specification version 2026-07-28 and may be removed in a future version. See SEP-2577 for more information.";
+    public const string DeprecatedLogging_Message = "The Logging feature is deprecated as of specification version 2026-07-28 and may be removed in a future version. See SEP-2577 for more information.";
 }

src/ModelContextProtocol.Core/AIContentExtensions.cs

@@ -34,6 +34,7 @@ public static class AIContentExtensions
     /// </para>
     /// </remarks>
     /// <exception cref="ArgumentNullException"><paramref name="chatClient"/> is <see langword="null"/>.</exception>
+    [Obsolete(Obsoletions.DeprecatedSampling_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
     public static Func<CreateMessageRequestParams?, IProgress<ProgressNotificationValue>, CancellationToken, ValueTask<CreateMessageResult>> CreateSamplingHandler(
         this IChatClient chatClient,
         JsonSerializerOptions? serializerOptions = null)

src/ModelContextProtocol.Core/Client/McpClient.Methods.cs

@@ -1208,6 +1208,7 @@ public async ValueTask<ResultOrCreatedTask<CallToolResult>> CallToolRawAsync(
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns>A task representing the asynchronous operation.</returns>
     /// <exception cref="McpException">The request failed or the server returned an error response.</exception>
+    [Obsolete(Obsoletions.DeprecatedLogging_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
     public Task SetLoggingLevelAsync(LogLevel level, RequestOptions? options = null, CancellationToken cancellationToken = default) =>
         SetLoggingLevelAsync(McpServerImpl.ToLoggingLevel(level), options, cancellationToken);
 
@@ -1219,6 +1220,7 @@ public Task SetLoggingLevelAsync(LogLevel level, RequestOptions? options = null,
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns>A task representing the asynchronous operation.</returns>
     /// <exception cref="McpException">The request failed or the server returned an error response.</exception>
+    [Obsolete(Obsoletions.DeprecatedLogging_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
     public Task SetLoggingLevelAsync(LoggingLevel level, RequestOptions? options = null, CancellationToken cancellationToken = default)
     {
         return SetLoggingLevelAsync(
@@ -1238,6 +1240,7 @@ public Task SetLoggingLevelAsync(LoggingLevel level, RequestOptions? options = n
     /// <returns>The result of the request.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="requestParams"/> is <see langword="null"/>.</exception>
     /// <exception cref="McpException">The request failed or the server returned an error response.</exception>
+    [Obsolete(Obsoletions.DeprecatedLogging_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
     public Task SetLoggingLevelAsync(
         SetLevelRequestParams requestParams,
         CancellationToken cancellationToken = default)

src/ModelContextProtocol.Core/Client/McpClientHandlers.cs

@@ -1,4 +1,4 @@
-using Microsoft.Extensions.AI;
+using Microsoft.Extensions.AI;
 using ModelContextProtocol.Protocol;
 using System.Diagnostics.CodeAnalysis;
 
@@ -50,6 +50,7 @@ public sealed class McpClientHandlers
     /// This handler is invoked when the server sends a <see cref="RequestMethods.RootsList"/> request to retrieve available roots.
     /// The handler receives request parameters and should return a <see cref="ListRootsResult"/> containing the collection of available roots.
     /// </remarks>
+    [Obsolete(Obsoletions.DeprecatedRoots_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
     public Func<ListRootsRequestParams?, CancellationToken, ValueTask<ListRootsResult>>? RootsHandler { get; set; }
 
     /// <summary>
@@ -85,5 +86,6 @@ public sealed class McpClientHandlers
     /// method with any implementation of <see cref="IChatClient"/>.
     /// </para>
     /// </remarks>
+    [Obsolete(Obsoletions.DeprecatedSampling_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
     public Func<CreateMessageRequestParams?, IProgress<ProgressNotificationValue>, CancellationToken, ValueTask<CreateMessageResult>>? SamplingHandler { get; set; }
 }

src/ModelContextProtocol.Core/ModelContextProtocol.Core.csproj

@@ -9,6 +9,11 @@
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <!-- Suppress the experimental extensions warning -->
     <NoWarn>$(NoWarn);MCPEXP001</NoWarn>
+    <!-- Core implements the Roots, Sampling, and Logging features deprecated by SEP-2577 (MCP9005).
+         The deprecated types remain in the source-generated JsonSerializerContext and are used throughout
+         the implementation, so the obsolete-usage diagnostic is suppressed project-wide here while staying
+         active for external consumers of the package. -->
+    <NoWarn>$(NoWarn);MCP9005</NoWarn>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(TargetFramework)' != 'netstandard2.0'">

src/ModelContextProtocol.Core/Protocol/ClientCapabilities.cs

@@ -52,13 +52,15 @@ public sealed class ClientCapabilities
     /// </para>
     /// </remarks>
     [JsonPropertyName("roots")]
+    [Obsolete(Obsoletions.DeprecatedRoots_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
     public RootsCapability? Roots { get; set; }
 
     /// <summary>
     /// Gets or sets the client's sampling capability, which indicates whether the client
     /// supports issuing requests to an LLM on behalf of the server.
     /// </summary>
     [JsonPropertyName("sampling")]
+    [Obsolete(Obsoletions.DeprecatedSampling_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
     public SamplingCapability? Sampling { get; set; }
 
     /// <summary>

src/ModelContextProtocol.Core/Protocol/ContentBlock.cs

@@ -760,6 +760,9 @@ public sealed class ResourceLinkBlock : ContentBlock
 
 /// <summary>Represents a request from the assistant to call a tool.</summary>
 [DebuggerDisplay("Name = {Name}, Id = {Id}")]
+// Sampling support type: this content block only appears inside sampling messages (an assistant tool call),
+// so it is deprecated together with sampling per SEP-2577.
+[Obsolete(Obsoletions.DeprecatedSampling_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
 public sealed class ToolUseContentBlock : ContentBlock
 {
     /// <inheritdoc/>
@@ -789,6 +792,9 @@ public sealed class ToolUseContentBlock : ContentBlock
 
 /// <summary>Represents the result of a tool use, provided by the user back to the assistant.</summary>
 [DebuggerDisplay("{DebuggerDisplay,nq}")]
+// Sampling support type: this content block only appears inside sampling messages (a tool result returned to
+// the assistant), so it is deprecated together with sampling per SEP-2577.
+[Obsolete(Obsoletions.DeprecatedSampling_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
 public sealed class ToolResultContentBlock : ContentBlock
 {
     /// <inheritdoc/>