diff --git a/packages/client/src/client/auth.ts b/packages/client/src/client/auth.ts
index 1a021be18..0391e35e9 100644
--- a/packages/client/src/client/auth.ts
+++ b/packages/client/src/client/auth.ts
@@ -1439,6 +1439,10 @@ export async function executeTokenRequest(
         applyClientAuthentication(authMethod, clientInformation as OAuthClientInformation, headers, tokenRequestParams);
     }
 
+    // Ensure Content-Type is always form-urlencoded for the token endpoint (OAuth 2.1 §3.2).
+    // Some addClientAuthentication implementations may have inadvertently set a different value.
+    headers.set('Content-Type', 'application/x-www-form-urlencoded');
+
     const response = await (fetchFn ?? fetch)(tokenUrl, {
         method: 'POST',
         headers,
diff --git a/packages/server/src/server/mcp.ts b/packages/server/src/server/mcp.ts
index 4d9f81c50..db0fb73d5 100644
--- a/packages/server/src/server/mcp.ts
+++ b/packages/server/src/server/mcp.ts
@@ -13,6 +13,7 @@ import type {
     ListResourcesResult,
     ListToolsResult,
     LoggingMessageNotification,
+    NotificationOptions,
     Prompt,
     PromptReference,
     ReadResourceResult,
@@ -973,27 +974,27 @@ export class McpServer {
     /**
      * Sends a resource list changed event to the client, if connected.
      */
-    sendResourceListChanged() {
+    sendResourceListChanged(options?: NotificationOptions) {
         if (this.isConnected()) {
-            this.server.sendResourceListChanged();
+            this.server.sendResourceListChanged(options);
         }
     }
 
     /**
      * Sends a tool list changed event to the client, if connected.
      */
-    sendToolListChanged() {
+    sendToolListChanged(options?: NotificationOptions) {
         if (this.isConnected()) {
-            this.server.sendToolListChanged();
+            this.server.sendToolListChanged(options);
         }
     }
 
     /**
      * Sends a prompt list changed event to the client, if connected.
      */
-    sendPromptListChanged() {
+    sendPromptListChanged(options?: NotificationOptions) {
         if (this.isConnected()) {
-            this.server.sendPromptListChanged();
+            this.server.sendPromptListChanged(options);
         }
     }
 }
diff --git a/packages/server/src/server/server.ts b/packages/server/src/server/server.ts
index f1a1851f4..102894c3a 100644
--- a/packages/server/src/server/server.ts
+++ b/packages/server/src/server/server.ts
@@ -660,17 +660,17 @@ export class Server extends Protocol<ServerContext> {
         });
     }
 
-    async sendResourceListChanged() {
+    async sendResourceListChanged(options?: NotificationOptions) {
         return this.notification({
             method: 'notifications/resources/list_changed'
-        });
+        }, options);
     }
 
-    async sendToolListChanged() {
-        return this.notification({ method: 'notifications/tools/list_changed' });
+    async sendToolListChanged(options?: NotificationOptions) {
+        return this.notification({ method: 'notifications/tools/list_changed' }, options);
     }
 
-    async sendPromptListChanged() {
-        return this.notification({ method: 'notifications/prompts/list_changed' });
+    async sendPromptListChanged(options?: NotificationOptions) {
+        return this.notification({ method: 'notifications/prompts/list_changed' }, options);
     }
 }