diff --git a/src/aws_durable_execution_sdk_python_testing/web/handlers.py b/src/aws_durable_execution_sdk_python_testing/web/handlers.py
index 85417e8..a3b2f0e 100644
--- a/src/aws_durable_execution_sdk_python_testing/web/handlers.py
+++ b/src/aws_durable_execution_sdk_python_testing/web/handlers.py
@@ -187,13 +187,11 @@ def _no_content_response(
     def _parse_callback_result_payload(self, request: HTTPRequest) -> bytes:
         """Parse callback result payload from request body.
 
-        Expects JSON payload with base64-encoded Result field.
-
         Args:
-            request: The HTTP request containing the JSON payload
+            request: The HTTP request containing the binary payload
 
         Returns:
-            bytes: The decoded result payload
+            bytes: The result payload
 
         Raises:
             InvalidParameterValueException: If payload parsing fails
@@ -201,19 +199,7 @@ def _parse_callback_result_payload(self, request: HTTPRequest) -> bytes:
         if not request.body or not isinstance(request.body, bytes):
             return b""
 
-        try:
-            payload = json.loads(request.body.decode("utf-8"))
-            if isinstance(payload, dict) and "Result" in payload:
-                result_value = payload["Result"]
-                if isinstance(result_value, str):
-                    return base64.b64decode(result_value)
-            return b""
-        except (json.JSONDecodeError, UnicodeDecodeError) as e:
-            msg = f"Failed to parse JSON payload: {e}"
-            raise InvalidParameterValueException(msg) from e
-        except ValueError as e:
-            msg = f"Failed to decode base64 result: {e}"
-            raise InvalidParameterValueException(msg) from e
+        return request.body
 
     def _parse_query_param(self, request: HTTPRequest, param_name: str) -> str | None:
         """Parse a single query parameter from the request.
diff --git a/tests/web/handlers_test.py b/tests/web/handlers_test.py
index 52c2dea..167b0f5 100644
--- a/tests/web/handlers_test.py
+++ b/tests/web/handlers_test.py
@@ -2039,13 +2039,13 @@ def test_send_durable_execution_callback_success_handler():
     assert isinstance(route, CallbackSuccessRoute)
     assert route.callback_id == "test-callback-id"
 
-    result_data = base64.b64encode(b"success-result").decode("utf-8")
-    request_body = json.dumps({"Result": result_data}).encode("utf-8")
+    # Result is sent as raw binary body
+    request_body = b"success-result"
 
     request = HTTPRequest(
         method="POST",
         path=route,
-        headers={"Content-Type": "application/json"},
+        headers={},
         query_params={},
         body=request_body,
     )
@@ -2062,57 +2062,6 @@ def test_send_durable_execution_callback_success_handler():
     )
 
 
-def test_send_durable_execution_callback_success_handler_invalid_json():
-    """Test SendDurableExecutionCallbackSuccessHandler with invalid JSON."""
-    executor = Mock()
-    handler = SendDurableExecutionCallbackSuccessHandler(executor)
-
-    router = Router()
-    route = router.find_route(
-        "/2025-12-01/durable-execution-callbacks/test-callback-id/succeed", "POST"
-    )
-
-    request = HTTPRequest(
-        method="POST",
-        path=route,
-        headers={"Content-Type": "application/json"},
-        query_params={},
-        body=b"invalid-json",
-    )
-
-    response = handler.handle(route, request)
-
-    assert response.status_code == 400
-    assert response.body["Type"] == "InvalidParameterValueException"
-    assert "Failed to parse JSON payload" in response.body["message"]
-
-
-def test_send_durable_execution_callback_success_handler_invalid_base64():
-    """Test SendDurableExecutionCallbackSuccessHandler with invalid base64."""
-    executor = Mock()
-    handler = SendDurableExecutionCallbackSuccessHandler(executor)
-
-    router = Router()
-    route = router.find_route(
-        "/2025-12-01/durable-execution-callbacks/test-callback-id/succeed", "POST"
-    )
-
-    request_body = json.dumps({"Result": "invalid-base64!"}).encode("utf-8")
-    request = HTTPRequest(
-        method="POST",
-        path=route,
-        headers={"Content-Type": "application/json"},
-        query_params={},
-        body=request_body,
-    )
-
-    response = handler.handle(route, request)
-
-    assert response.status_code == 400
-    assert response.body["Type"] == "InvalidParameterValueException"
-    assert "Failed to decode base64 result" in response.body["message"]
-
-
 def test_send_durable_execution_callback_success_handler_empty_body():
     """Test SendDurableExecutionCallbackSuccessHandler with empty body."""
     executor = Mock()