diff --git a/MCPForUnity/Editor/Helpers/CodexConfigHelper.cs b/MCPForUnity/Editor/Helpers/CodexConfigHelper.cs
index b4f786ee..786bc7f9 100644
--- a/MCPForUnity/Editor/Helpers/CodexConfigHelper.cs
+++ b/MCPForUnity/Editor/Helpers/CodexConfigHelper.cs
@@ -29,6 +29,9 @@ public static string BuildCodexServerBlock(string uvPath)
                 // HTTP mode: Use url field
                 string httpUrl = HttpEndpointUtility.GetMcpRpcUrl();
                 unityMCP["url"] = new TomlString { Value = httpUrl };
+
+                // Enable Codex's Rust MCP client for HTTP/SSE transport
+                EnsureRmcpClientFeature(table);
             }
             else
             {
@@ -71,6 +74,8 @@ public static string UpsertCodexServerBlock(string existingToml, string uvPath)
             // Parse existing TOML or create new root table
             var root = TryParseToml(existingToml) ?? new TomlTable();
 
+            bool useHttpTransport = EditorPrefs.GetBool(MCPForUnity.Editor.Constants.EditorPrefKeys.UseHttpTransport, true);
+
             // Ensure mcp_servers table exists
             if (!root.TryGetNode("mcp_servers", out var mcpServersNode) || !(mcpServersNode is TomlTable))
             {
@@ -81,6 +86,11 @@ public static string UpsertCodexServerBlock(string existingToml, string uvPath)
             // Create or update unityMCP table
             mcpServers["unityMCP"] = CreateUnityMcpTable(uvPath);
 
+            if (useHttpTransport)
+            {
+                EnsureRmcpClientFeature(root);
+            }
+
             // Serialize back to TOML
             using var writer = new StringWriter();
             root.WriteTo(writer);
@@ -200,6 +210,22 @@ private static TomlTable CreateUnityMcpTable(string uvPath)
             return unityMCP;
         }
 
+        /// <summary>
+        /// Ensures the features table contains the rmcp_client flag for HTTP/SSE transport.
+        /// </summary>
+        private static void EnsureRmcpClientFeature(TomlTable root)
+        {
+            if (root == null) return;
+
+            if (!root.TryGetNode("features", out var featuresNode) || featuresNode is not TomlTable features)
+            {
+                features = new TomlTable();
+                root["features"] = features;
+            }
+
+            features["rmcp_client"] = new TomlBoolean { Value = true };
+        }
+
         private static bool TryGetTable(TomlTable parent, string key, out TomlTable table)
         {
             table = null;
diff --git a/TestProjects/UnityMCPTests/Assets/Tests/EditMode/Helpers/CodexConfigHelperTests.cs b/TestProjects/UnityMCPTests/Assets/Tests/EditMode/Helpers/CodexConfigHelperTests.cs
index 92f85866..a186e115 100644
--- a/TestProjects/UnityMCPTests/Assets/Tests/EditMode/Helpers/CodexConfigHelperTests.cs
+++ b/TestProjects/UnityMCPTests/Assets/Tests/EditMode/Helpers/CodexConfigHelperTests.cs
@@ -462,6 +462,14 @@ public void BuildCodexServerBlock_HttpMode_GeneratesUrlField()
             Assert.IsInstanceOf<TomlTable>(unityMcpNode, "unityMCP should be a table");
 
             var unityMcp = unityMcpNode as TomlTable;
+
+            // Verify features.rmcp_client is enabled for HTTP transport
+            Assert.IsTrue(parsed.TryGetNode("features", out var featuresNode), "HTTP mode should include features table");
+            Assert.IsInstanceOf<TomlTable>(featuresNode, "features should be a table");
+            var features = featuresNode as TomlTable;
+            Assert.IsTrue(features.TryGetNode("rmcp_client", out var rmcpNode), "features should include rmcp_client flag");
+            Assert.IsInstanceOf<TomlBoolean>(rmcpNode, "rmcp_client should be a boolean");
+            Assert.IsTrue((rmcpNode as TomlBoolean).Value, "rmcp_client should be true");
             
             // Verify url field is present
             Assert.IsTrue(unityMcp.TryGetNode("url", out var urlNode), "unityMCP should contain url in HTTP mode");
@@ -536,6 +544,14 @@ public void UpsertCodexServerBlock_HttpMode_GeneratesUrlField()
 
             var unityMcp = unityMcpNode as TomlTable;
 
+            // Verify features.rmcp_client is enabled for HTTP transport
+            Assert.IsTrue(parsed.TryGetNode("features", out var featuresNode), "HTTP mode should include features table");
+            Assert.IsInstanceOf<TomlTable>(featuresNode, "features should be a table");
+            var features = featuresNode as TomlTable;
+            Assert.IsTrue(features.TryGetNode("rmcp_client", out var rmcpNode), "features should include rmcp_client flag");
+            Assert.IsInstanceOf<TomlBoolean>(rmcpNode, "rmcp_client should be a boolean");
+            Assert.IsTrue((rmcpNode as TomlBoolean).Value, "rmcp_client should be true");
+
             // Verify url field is present
             Assert.IsTrue(unityMcp.TryGetNode("url", out var urlNode), "unityMCP should contain url in HTTP mode");
             Assert.IsInstanceOf<TomlString>(urlNode, "url should be a string");