diff --git a/python_modules/dagster-ext/dagster_ext/__init__.py b/python_modules/dagster-ext/dagster_ext/__init__.py
index 38366a039aeaf..323c3877e90a4 100644
--- a/python_modules/dagster-ext/dagster_ext/__init__.py
+++ b/python_modules/dagster-ext/dagster_ext/__init__.py
@@ -39,6 +39,9 @@
 # ##### PROTOCOL
 # ########################
 
+# This represents the version of the protocol, rather than the version of the package. It must be
+# manually updated whenever there are changes to the protocol.
+PROTOCOL_VERSION = "0.1"
 
 ExtExtras = Mapping[str, Any]
 ExtParams = Mapping[str, Any]
@@ -64,6 +67,7 @@ def _param_name_to_env_key(key: str) -> str:
 
 
 class ExtMessage(TypedDict):
+    __dagster_ext_version: str
     method: str
     params: Optional[Mapping[str, Any]]
 
@@ -677,7 +681,7 @@ def __init__(
         self._materialized_assets: set[str] = set()
 
     def _write_message(self, method: str, params: Optional[Mapping[str, Any]] = None) -> None:
-        message = ExtMessage(method=method, params=params)
+        message = ExtMessage(__dagster_ext_version=PROTOCOL_VERSION, method=method, params=params)
         self._message_channel.write_message(message)
 
     # ########################