diff --git a/api/services/variable_truncator.py b/api/services/variable_truncator.py
index 93a032498d..00aa31650c 100644
--- a/api/services/variable_truncator.py
+++ b/api/services/variable_truncator.py
@@ -1,9 +1,8 @@
 from __future__ import annotations
 
 import dataclasses
-from abc import ABC, abstractmethod
 from collections.abc import Mapping
-from typing import Any, overload, override
+from typing import Any, Protocol, overload, override
 
 from configs import dify_config
 from graphon.file import File
@@ -66,14 +65,12 @@ class TruncationResult:
     truncated: bool
 
 
-class BaseTruncator(ABC):
-    @abstractmethod
-    def truncate(self, segment: Segment) -> TruncationResult:
-        pass
+class BaseTruncator(Protocol):
+    """Protocol for variable truncation strategies."""
 
-    @abstractmethod
-    def truncate_variable_mapping(self, v: Mapping[str, Any]) -> tuple[Mapping[str, Any], bool]:
-        pass
+    def truncate(self, segment: Segment) -> TruncationResult: ...
+
+    def truncate_variable_mapping(self, v: Mapping[str, Any]) -> tuple[Mapping[str, Any], bool]: ...
 
 
 class VariableTruncator(BaseTruncator):
diff --git a/api/tests/unit_tests/services/test_variable_truncator_additional.py b/api/tests/unit_tests/services/test_variable_truncator_additional.py
index e9427c4ab3..50644d4294 100644
--- a/api/tests/unit_tests/services/test_variable_truncator_additional.py
+++ b/api/tests/unit_tests/services/test_variable_truncator_additional.py
@@ -1,4 +1,3 @@
-from collections.abc import Mapping
 from typing import Any
 
 import pytest
@@ -7,26 +6,7 @@ from graphon.nodes.variable_assigner.common.helpers import UpdatedVariable
 from graphon.variables.segments import IntegerSegment, ObjectSegment, StringSegment
 from graphon.variables.types import SegmentType
 from services import variable_truncator as truncator_module
-from services.variable_truncator import BaseTruncator, TruncationResult, VariableTruncator
-
-
-class _AbstractPassthrough(BaseTruncator):
-    def truncate(self, segment: Any) -> TruncationResult:
-        return super().truncate(segment)  # type: ignore[misc]
-
-    def truncate_variable_mapping(self, v: Mapping[str, Any]) -> tuple[Mapping[str, Any], bool]:
-        return super().truncate_variable_mapping(v)  # type: ignore[misc]
-
-
-class TestBaseTruncatorContract:
-    def test_base_truncator_methods_should_execute_abstract_placeholders(self) -> None:
-        passthrough = _AbstractPassthrough()
-
-        truncate_result = passthrough.truncate(StringSegment(value="x"))
-        mapping_result = passthrough.truncate_variable_mapping({"a": 1})
-
-        assert truncate_result is None
-        assert mapping_result is None
+from services.variable_truncator import VariableTruncator
 
 
 class TestVariableTruncatorAdditionalBehavior: