diff --git a/libs/sdk-py/langgraph_sdk/auth/types.py b/libs/sdk-py/langgraph_sdk/auth/types.py
index 84211878d..699c4ef2e 100644
--- a/libs/sdk-py/langgraph_sdk/auth/types.py
+++ b/libs/sdk-py/langgraph_sdk/auth/types.py
@@ -218,6 +218,8 @@ class BaseUser(typing.Protocol):
 class StudioUser:
     """A user object that's populated from authenticated requests from the LangGraph studio.
 
+    `ls_user_id` is the canonical LangSmith user ID when supplied by Agent Server.
+
     Note: Studio auth can be disabled in your `langgraph.json` config.
 
     ```json
@@ -250,10 +252,11 @@ class StudioUser:
         ```
     """
 
-    __slots__ = ("_is_authenticated", "_permissions", "username")
+    __slots__ = ("_is_authenticated", "_permissions", "ls_user_id", "username")
 
     def __init__(self, username: str, is_authenticated: bool = False) -> None:
         self.username = username
+        self.ls_user_id: str | None = None
         self._is_authenticated = is_authenticated
         self._permissions = ["authenticated"] if is_authenticated else []
 
diff --git a/libs/sdk-py/tests/test_auth.py b/libs/sdk-py/tests/test_auth.py
index 82b243ce5..bf1014500 100644
--- a/libs/sdk-py/tests/test_auth.py
+++ b/libs/sdk-py/tests/test_auth.py
@@ -1,8 +1,22 @@
 import pytest
+from typing_extensions import assert_type
 
 from langgraph_sdk import Auth
 
 
+def test_studio_user_langsmith_id() -> None:
+    def langsmith_id(user: object) -> str | None:
+        if isinstance(user, Auth.types.StudioUser):
+            return assert_type(user.ls_user_id, str | None)
+        return None
+
+    user = Auth.types.StudioUser("login-user", is_authenticated=True)
+    assert langsmith_id(user) is None
+    user.ls_user_id = "langsmith-user"
+    assert langsmith_id(user) == "langsmith-user"
+    assert user.identity == "login-user"
+
+
 def test_handler_multiple_resources_and_actions() -> None:
     auth = Auth()