diff --git a/src/agent/client.ts b/src/agent/client.ts
index 031243c..6b0c331 100644
--- a/src/agent/client.ts
+++ b/src/agent/client.ts
@@ -59,5 +59,9 @@ export async function getClient() {
     settingsManager.updateSettings({ env: updatedEnv });
   }
 
-  return new Letta({ apiKey, baseURL });
+  return new Letta({
+    apiKey,
+    baseURL,
+    defaultHeaders: { "X-Letta-Source": "letta-code" },
+  });
 }
diff --git a/src/auth/oauth.ts b/src/auth/oauth.ts
index f433631..606f064 100644
--- a/src/auth/oauth.ts
+++ b/src/auth/oauth.ts
@@ -201,7 +201,11 @@ export async function validateCredentials(
 ): Promise<boolean> {
   try {
     // Create a temporary client to test authentication
-    const client = new Letta({ apiKey, baseURL: baseUrl });
+    const client = new Letta({
+      apiKey,
+      baseURL: baseUrl,
+      defaultHeaders: { "X-Letta-Source": "letta-code" },
+    });
 
     // Try to list agents - this requires valid authentication
     await client.agents.list({ limit: 1 });
diff --git a/src/tests/agent/link-unlink.test.ts b/src/tests/agent/link-unlink.test.ts
index 7a4817b..5ebce82 100644
--- a/src/tests/agent/link-unlink.test.ts
+++ b/src/tests/agent/link-unlink.test.ts
@@ -23,7 +23,10 @@ describeOrSkip("Link/Unlink Tools", () => {
       throw new Error("LETTA_API_KEY required for tests");
     }
 
-    client = new Letta({ apiKey });
+    client = new Letta({
+      apiKey,
+      defaultHeaders: { "X-Letta-Source": "letta-code" },
+    });
 
     const agent = await client.agents.create({
       model: "openai/gpt-4o-mini",