diff --git a/libs/core/langchain_core/language_models/chat_models.py b/libs/core/langchain_core/language_models/chat_models.py
index 3f264e854d5..b9f5c799b07 100644
--- a/libs/core/langchain_core/language_models/chat_models.py
+++ b/libs/core/langchain_core/language_models/chat_models.py
@@ -311,14 +311,16 @@ class BaseChatModel(BaseLanguageModel[BaseMessage], ABC):
     does not properly support streaming.
     """
 
-    output_version: str = "v0"
+    output_version: Literal["v0", "v1"] = "v0"
     """Version of AIMessage output format to use.
 
     This field is used to roll-out new output formats for chat model AIMessages
     in a backwards-compatible way.
 
-    All chat models currently support the default of ``"v0"``. Chat model subclasses
-    can override with (customizable) supported values.
+    ``'v1'`` standardizes output format using a list of typed ContentBlock dicts. We
+    recommend this for new applications.
+
+    All chat models currently support the default of ``"v0"``.
 
     .. versionadded:: 0.3.68
     """