diff --git a/datadog_lambda/durable.py b/datadog_lambda/durable.py
index e9443f92..3acc7c0c 100644
--- a/datadog_lambda/durable.py
+++ b/datadog_lambda/durable.py
@@ -41,9 +41,13 @@ def extract_durable_function_tags(event):
     if not parsed:
         logger.error("Failed to parse DurableExecutionArn: %s", durable_execution_arn)
         return {}
-
     execution_name, execution_id = parsed
+    # Use the number of operations to determine if it's the first invocation. This is
+    # what the durable execution SDK does to determine the replay status.
+    operations = event.get("InitialExecutionState", {}).get("Operations", [])
+    is_first_invocation = len(operations) == 1
     return {
         "durable_function_execution_name": execution_name,
         "durable_function_execution_id": execution_id,
+        "durable_function_first_invocation": str(is_first_invocation).lower(),
     }
diff --git a/tests/test_durable.py b/tests/test_durable.py
index 60914934..0887e2d9 100644
--- a/tests/test_durable.py
+++ b/tests/test_durable.py
@@ -45,11 +45,12 @@ def test_works_with_numeric_version_qualifier(self):
 
 
 class TestExtractDurableFunctionTags(unittest.TestCase):
-    def test_extracts_tags_from_event_with_durable_execution_arn(self):
+    def test_sets_first_invocation_true_when_only_execution_operation(self):
+        # One operation (the current EXECUTION operation itself) → not replaying → first invocation
         event = {
             "DurableExecutionArn": "arn:aws:lambda:us-east-1:123456789012:function:my-func:1/durable-execution/my-execution/550e8400-e29b-41d4-a716-446655440004",
             "CheckpointToken": "some-token",
-            "InitialExecutionState": {"Operations": []},
+            "InitialExecutionState": {"Operations": [{"OperationType": "EXECUTION"}]},
         }
         result = extract_durable_function_tags(event)
         self.assertEqual(
@@ -57,6 +58,29 @@ def test_extracts_tags_from_event_with_durable_execution_arn(self):
             {
                 "durable_function_execution_name": "my-execution",
                 "durable_function_execution_id": "550e8400-e29b-41d4-a716-446655440004",
+                "durable_function_first_invocation": "true",
+            },
+        )
+
+    def test_sets_first_invocation_false_when_multiple_operations(self):
+        # More than one operation → replaying → not first invocation
+        event = {
+            "DurableExecutionArn": "arn:aws:lambda:us-east-1:123456789012:function:my-func:1/durable-execution/my-execution/550e8400-e29b-41d4-a716-446655440004",
+            "CheckpointToken": "some-token",
+            "InitialExecutionState": {
+                "Operations": [
+                    {"OperationType": "EXECUTION"},
+                    {"OperationType": "STEP"},
+                ]
+            },
+        }
+        result = extract_durable_function_tags(event)
+        self.assertEqual(
+            result,
+            {
+                "durable_function_execution_name": "my-execution",
+                "durable_function_execution_id": "550e8400-e29b-41d4-a716-446655440004",
+                "durable_function_first_invocation": "false",
             },
         )