diff --git a/reme_ai/core/context/runtime_context.py b/reme_ai/core/context/runtime_context.py
index b2362161..d7112e1c 100644
--- a/reme_ai/core/context/runtime_context.py
+++ b/reme_ai/core/context/runtime_context.py
@@ -27,11 +27,8 @@ class RuntimeContext(BaseContext):
         if context is None:
             return cls(**kwargs)
 
-        new_instance = cls(response=context.response, stream_queue=context.stream_queue)
-        new_instance.update(context)
-        if kwargs:
-            new_instance.update(kwargs)
-        return new_instance
+        context.update(kwargs)
+        return context
 
     async def _enqueue(self, chunk: StreamChunk) -> None:
         """Internal helper to put a chunk into the queue if it exists."""
diff --git a/reme_ai/core/op/base_op.py b/reme_ai/core/op/base_op.py
index e5f8450e..26f1e7f5 100644
--- a/reme_ai/core/op/base_op.py
+++ b/reme_ai/core/op/base_op.py
@@ -4,15 +4,15 @@ import asyncio
 import copy
 import inspect
 from pathlib import Path
-from typing import Callable, Any, Union
+from typing import Callable, Any, Optional
 
 from loguru import logger
 from tqdm import tqdm
 
-from ..context import RuntimeContext, PromptHandler, C, BaseContext
+from ..context import RuntimeContext, PromptHandler, C
 from ..embedding import BaseEmbeddingModel
 from ..llm import BaseLLM
-from ..schema import ToolCall, ToolAttr
+from ..schema import ToolCall, ToolAttr, Response
 from ..token_counter import BaseTokenCounter
 from ..utils import camel_to_snake, CacheHandler, timer
 from ..vector_store import BaseVectorStore
@@ -40,10 +40,10 @@ class BaseOp:
         token_counter: str | BaseTokenCounter = "default",
         enable_cache: bool = False,
         cache_path: str = "cache/op",
-        sub_ops: Union[list["BaseOp"], dict[str, "BaseOp"], "BaseOp", None] = None,
+        sub_ops: dict[str, "BaseOp"] | list["BaseOp"] | Optional["BaseOp"] = None,
         input_mapping: dict[str, str] | None = None,
         output_mapping: dict[str, str] | None = None,
-        enable_tool_response: bool = False,
+        save_response_result: bool = False,
         enable_sync_thread_pool: bool = True,
         max_retries: int = 1,
         raise_exception: bool = False,
@@ -62,12 +62,12 @@ class BaseOp:
 
         self.enable_cache = enable_cache
         self.cache_path = cache_path
-        self.sub_ops = BaseContext[str, BaseOp]()
+        self.sub_ops: list[BaseOp] = []
         self.add_sub_ops(sub_ops)
 
         self.input_mapping = input_mapping
         self.output_mapping = output_mapping
-        self.enable_tool_response = enable_tool_response
+        self.save_response_result = save_response_result
         self.enable_sync_thread_pool = enable_sync_thread_pool
         self.max_retries = max(1, max_retries)
         self.raise_exception = raise_exception
@@ -89,7 +89,7 @@ class BaseOp:
 
     def _validate_inputs(self):
         """Ensure all required tool inputs are present in context."""
-        if self.tool_call:
+        if self.tool_call is not None:
             parameters = self.tool_call.parameters
             if parameters.type == "object" and parameters.properties:
                 required_list = parameters.required or []
@@ -98,30 +98,47 @@ class BaseOp:
 
     def _handle_failure(self, e: Exception, attempt: int):
         """Log failures and handle final retry logic."""
-        logger.exception(f"{self.name} failed (attempt {attempt + 1}): {e}")
+        message = f"{self.name} failed (attempt {attempt + 1}): {e}"
         if attempt == self.max_retries - 1:
+            logger.exception(message)
             if self.raise_exception:
                 raise e
 
-            if self.tool_call:
+            if self.tool_call is not None:
                 self.output = f"{self.name} failed: {e}"
+        else:
+            logger.warning(message)
 
     @property
-    def tool_call(self) -> ToolCall:
+    def tool_call(self) -> ToolCall | None:
         """Lazily construct and return the tool call metadata."""
         if self._tool_call is None:
             self._tool_call = self._build_tool_call()
-            assert self._tool_call, "tool_call is not defined!"
+            if self._tool_call is None:
+                return None
+
             self._tool_call.name = self._tool_call.name or self.name
             if not self._tool_call.output.properties:
-                self._tool_call.output = ToolAttr(
-                    type="object",
-                    properties={
-                        f"{self.name}_result": ToolAttr(type="string", description=f"Execution result of {self.name}"),
-                    },
-                )
+                self._tool_call.output.properties = {
+                    f"{self.name}_result": ToolAttr(type="string", description=f"Execution result of {self.name}"),
+                }
         return self._tool_call
 
+    def set_tool_call(self, tool_call: ToolCall | dict):
+        """Set the tool call."""
+        if isinstance(tool_call, dict):
+            self._tool_call = ToolCall(**tool_call)
+        elif isinstance(tool_call, ToolCall):
+            self._tool_call = tool_call
+        else:
+            raise ValueError(f"Invalid tool call: {tool_call}")
+
+        self._tool_call.name = self._tool_call.name or self.name
+        if not self._tool_call.output.properties:
+            self._tool_call.output.properties = {
+                f"{self.name}_result": ToolAttr(type="string", description=f"Execution result of {self.name}"),
+            }
+
     @property
     def input_dict(self) -> dict:
         """Extract required and optional inputs from context based on schema."""
@@ -137,6 +154,7 @@ class BaseOp:
         output_properties = self.tool_call.output.properties
         if not output_properties:
             return None
+
         keys = list(output_properties.keys())
         return self.context[keys[0]]
 
@@ -146,6 +164,7 @@ class BaseOp:
         output_properties = self.tool_call.output.properties
         if not output_properties:
             return
+
         keys = list(output_properties.keys())
         self.context[keys[0]] = value
 
@@ -188,10 +207,7 @@ class BaseOp:
         """Lazily initialize and return the token counter instance."""
         if isinstance(self._token_counter, str):
             cfg = C.service_config.token_counter[self._token_counter]
-            self._token_counter = C.get_token_counter_class(cfg.backend)(
-                model_name=cfg.model_name,
-                **cfg.model_extra,
-            )
+            self._token_counter = C.get_token_counter_class(cfg.backend)(model_name=cfg.model_name, **cfg.model_extra)
         return self._token_counter
 
     @property
@@ -199,6 +215,11 @@ class BaseOp:
         """Get service configuration metadata."""
         return C.service_config.model_extra
 
+    @property
+    def response(self) -> Response:
+        """Get the response object."""
+        return self.context.response
+
     async def before_execute(self):
         """Prepare context and validate before async execution."""
         self.context.apply_mapping(self.input_mapping)
@@ -210,7 +231,7 @@ class BaseOp:
     async def after_execute(self):
         """Finalize context and mappings after async execution."""
         self.context.apply_mapping(self.output_mapping)
-        if self.tool_call and self.enable_tool_response:
+        if self.tool_call is not None and self.save_response_result:
             self.context.response.answer = self.output
 
         if not isinstance(self._llm, str) and hasattr(self._llm, "close"):
@@ -229,7 +250,7 @@ class BaseOp:
     def after_execute_sync(self):
         """Finalize context and mappings after sync execution."""
         self.context.apply_mapping(self.output_mapping)
-        if self.tool_call and self.enable_tool_response:
+        if self.tool_call is not None and self.save_response_result:
             self.context.response.answer = self.output
 
         if not isinstance(self._llm, str) and hasattr(self._llm, "close_sync"):
@@ -249,7 +270,7 @@ class BaseOp:
                 break
             except Exception as e:
                 self._handle_failure(e, i)
-        return self.output if self.tool_call else None
+        return self.output if self.tool_call is not None else None
 
     async def call(self, context: RuntimeContext = None, **kwargs):
         """Execute the operator asynchronously with retry logic."""
@@ -262,7 +283,7 @@ class BaseOp:
                 break
             except Exception as e:
                 self._handle_failure(e, i)
-        return self.output if self.tool_call else None
+        return self.output if self.tool_call is not None else None
 
     def submit_sync_task(self, fn: Callable, *args, **kwargs) -> "BaseOp":
         """Submit a task to the thread pool or local queue."""
@@ -301,23 +322,27 @@ class BaseOp:
         finally:
             self._pending_tasks.clear()
 
-    def add_sub_ops(self, sub_ops: Union[list["BaseOp"], dict[str, "BaseOp"], "BaseOp", None]):
-        """Add child operators to this operator's sub_ops context."""
+    def add_sub_ops(self, sub_ops: dict[str, "BaseOp"] | list["BaseOp"] | Optional["BaseOp"]):
+        """Add child operators to this operator's sub_ops."""
         if not sub_ops:
             return
 
         if isinstance(sub_ops, dict):
-            ops_dict = sub_ops
+            for name, op in sub_ops.items():
+                assert self.async_mode == op.async_mode, "Async mode mismatch!"
+                op.name = name
+                self.sub_ops.append(op)
+        elif isinstance(sub_ops, list):
+            for op in sub_ops:
+                assert self.async_mode == op.async_mode, "Async mode mismatch!"
+                self.sub_ops.append(op)
         else:
-            ops_dict = {op.name: op for op in (sub_ops if isinstance(sub_ops, list) else [sub_ops])}
-
-        for name, op in ops_dict.items():
-            assert self.async_mode == op.async_mode, "Async mode mismatch!"
-            self.sub_ops[name] = op
+            assert self.async_mode == sub_ops.async_mode, "Async mode mismatch!"
+            self.sub_ops.append(sub_ops)
 
     def add_sub_op(self, sub_op: "BaseOp"):
-        """Add a single child operator to this operator's sub_ops context."""
-        self.add_sub_ops(sub_op)
+        """Add a single child operator to this operator's sub_ops."""
+        self.sub_ops.append(sub_op)
 
     def __lshift__(self, ops):
         """Operator overload for adding sub-operators."""
@@ -350,7 +375,7 @@ class BaseOp:
 
     def copy(self, **kwargs):
         """Create a copy of this operator with optional parameter overrides."""
-        copy_op = self.__class__(*self._init_args, **self._init_kwargs, **kwargs)
+        copy_op = self.__class__(*self._init_args, **{**self._init_kwargs, **kwargs})
         if self.sub_ops:
             copy_op.sub_ops.clear()
             copy_op.add_sub_ops(self.sub_ops)
diff --git a/reme_ai/core/op/parallel_op.py b/reme_ai/core/op/parallel_op.py
index 746485ca..18b84d0c 100644
--- a/reme_ai/core/op/parallel_op.py
+++ b/reme_ai/core/op/parallel_op.py
@@ -8,14 +8,14 @@ class ParallelOp(BaseOp):
 
     async def execute(self):
         """Executes all sub-operations concurrently using asynchronous tasks."""
-        for op in self.sub_ops.values():
+        for op in self.sub_ops:
             assert op.async_mode
             self.submit_async_task(op.call, context=self.context)
         await self.join_async_tasks()
 
     def execute_sync(self):
         """Executes all sub-operations concurrently using synchronous task management."""
-        for op in self.sub_ops.values():
+        for op in self.sub_ops:
             assert not op.async_mode
             self.submit_sync_task(op.call_sync, context=self.context)
         self.join_sync_tasks()
diff --git a/reme_ai/core/op/sequential_op.py b/reme_ai/core/op/sequential_op.py
index 79243cff..3dabb0c9 100644
--- a/reme_ai/core/op/sequential_op.py
+++ b/reme_ai/core/op/sequential_op.py
@@ -8,13 +8,13 @@ class SequentialOp(BaseOp):
 
     async def execute(self):
         """Executes sub-operations sequentially using asynchronous awaits."""
-        for op in self.sub_ops.values():
+        for op in self.sub_ops:
             assert op.async_mode
             await op.call(context=self.context)
 
     def execute_sync(self):
         """Executes sub-operations sequentially in a synchronous blocking manner."""
-        for op in self.sub_ops.values():
+        for op in self.sub_ops:
             assert not op.async_mode
             op.call_sync(context=self.context)
 
diff --git a/reme_ai/core/tool/mcp_tool.py b/reme_ai/core/tool/mcp_tool.py
index f9afa029..90f6ad7b 100644
--- a/reme_ai/core/tool/mcp_tool.py
+++ b/reme_ai/core/tool/mcp_tool.py
@@ -20,7 +20,7 @@ class MCPTool(BaseOp):
         self,
         mcp_server: str = "",
         tool_name: str = "",
-        enable_tool_response: bool = True,
+        save_response_result: bool = True,
         parameter_required: List[str] | None = None,
         parameter_optional: List[str] | None = None,
         parameter_deleted: List[str] | None = None,
@@ -31,7 +31,7 @@ class MCPTool(BaseOp):
     ):
 
         super().__init__(
-            enable_tool_response=enable_tool_response,
+            save_response_result=save_response_result,
             max_retries=max_retries,
             raise_exception=raise_exception,
             **kwargs,
diff --git a/tests/test_op_composition.py b/tests/test_op_composition.py
new file mode 100644
index 00000000..8d32b51a
--- /dev/null
+++ b/tests/test_op_composition.py
@@ -0,0 +1,325 @@
+"""
+Unit tests for BaseOp and operator composition (>>, <<, |).
+Tests asynchronous execution mode.
+"""
+
+import asyncio
+
+from reme_ai.core.op import BaseOp
+from reme_ai.core.schema import ToolCall, ToolAttr
+
+
+class AddOp(BaseOp):
+    """Simple operator that adds a value to a number in context."""
+
+    def __init__(self, value: int = 1, **kwargs):
+        super().__init__(**kwargs)
+        self.value = value
+
+    def _build_tool_call(self) -> ToolCall:
+        return ToolCall(
+            **{
+                "name": self.name,
+                "description": f"Add {self.value} to input",
+                "parameters": ToolAttr(
+                    **{
+                        "type": "object",
+                        "properties": {
+                            "number": {"type": "integer", "description": "Input number"},
+                        },
+                        "required": ["number"],
+                    },
+                ),
+            },
+        )
+
+    async def execute(self):
+        """Async execution: add value to input number."""
+        self.context["number"] += self.value
+        self.output = self.context["number"]
+
+
+class MultiplyOp(BaseOp):
+    """Simple operator that multiplies a number in context."""
+
+    def __init__(self, factor: int = 2, **kwargs):
+        super().__init__(**kwargs)
+        self.factor = factor
+
+    def _build_tool_call(self) -> ToolCall:
+        return ToolCall(
+            **{
+                "name": self.name,
+                "description": f"Multiply by {self.factor}",
+                "parameters": ToolAttr(
+                    **{
+                        "type": "object",
+                        "properties": {
+                            "number": {"type": "integer", "description": "Input number"},
+                        },
+                        "required": ["number"],
+                    },
+                ),
+            },
+        )
+
+    async def execute(self):
+        """Async execution: multiply input number."""
+        self.context["number"] *= self.factor
+        self.output = self.context["number"]
+
+
+class AppendOp(BaseOp):
+    """Operator that appends a value to a list in context."""
+
+    def __init__(self, value: str = "", **kwargs):
+        super().__init__(**kwargs)
+        self.value = value
+
+    def _build_tool_call(self) -> ToolCall:
+        return ToolCall(
+            **{
+                "name": self.name,
+                "description": f"Append {self.value} to list",
+                "parameters": ToolAttr(
+                    **{
+                        "type": "object",
+                        "properties": {
+                            "items": {"type": "array", "description": "List of items"},
+                        },
+                        "required": ["items"],
+                    },
+                ),
+            },
+        )
+
+    async def execute(self):
+        """Async execution: append value to list."""
+        self.context["items"].append(self.value)
+        self.output = self.context["items"]
+
+
+async def test_basic_async_call():
+    """Test basic asynchronous operator execution."""
+    op = AddOp(value=5, name="add_5")
+    await op.call(number=10)
+    number = op.context["number"]
+    assert number == 15, f"Expected context result 15, got {number}"
+    print("✓ test_basic_async_call passed")
+
+
+async def test_sequential_composition_async():
+    """Test >> operator for sequential composition in async mode."""
+    add_op = AddOp(value=5, name="add_5")
+    multiply_op = MultiplyOp(factor=2, name="multiply_2")
+    composed = add_op >> multiply_op
+    await composed.call(number=10)
+
+    # (10 + 5) * 2 = 30
+    assert composed.context["number"] == 30, f"Expected 30, got {composed.context['number']}"
+    print("✓ test_sequential_composition_async passed")
+
+
+async def test_parallel_composition_async():
+    """Test | operator for parallel composition in async mode."""
+    append_a = AppendOp(value="A", name="append_a")
+    append_b = AppendOp(value="B", name="append_b")
+    append_c = AppendOp(value="C", name="append_c")
+
+    composed = append_a | append_b | append_c
+
+    await composed.call(items=[])
+
+    # All should append to the list
+    items = composed.context["items"]
+    assert len(items) == 3, f"Expected 3 items, got {len(items)}"
+    assert set(items) == {"A", "B", "C"}, f"Expected A,B,C, got {items}"
+    print("✓ test_parallel_composition_async passed")
+
+
+async def test_add_sub_ops_async():
+    """Test << operator for adding sub-operations in async mode."""
+    parent_op = BaseOp(name="parent")
+    child1 = AddOp(value=5, name="child1")
+    child2 = MultiplyOp(factor=2, name="child2")
+
+    _ = parent_op << child1
+    _ = parent_op << child2
+
+    assert len(parent_op.sub_ops) == 2, f"Expected 2 sub_ops, got {len(parent_op.sub_ops)}"
+    sub_op_names = [op.name for op in parent_op.sub_ops]
+    assert "child1" in sub_op_names, "child1 not in sub_ops"
+    assert "child2" in sub_op_names, "child2 not in sub_ops"
+    print("✓ test_add_sub_ops_async passed")
+
+
+async def test_add_sub_ops_dict():
+    """Test << operator with dictionary of operations."""
+    parent_op = BaseOp(name="parent")
+    ops_dict = {
+        "add": AddOp(value=5, name="add"),
+        "multiply": MultiplyOp(factor=2, name="multiply"),
+    }
+
+    _ = parent_op << ops_dict
+
+    assert len(parent_op.sub_ops) == 2, f"Expected 2 ops_dict, got {len(parent_op.sub_ops)}"
+    sub_op_names = [op.name for op in parent_op.sub_ops]
+    assert "add" in sub_op_names, "add not in ops_dict"
+    assert "multiply" in sub_op_names, "multiply not in ops_dict"
+    print("✓ test_add_sub_ops_dict passed")
+
+
+async def test_add_sub_ops_list():
+    """Test << operator with list of operations."""
+    parent_op = BaseOp(name="parent")
+    sub_ops = [
+        AddOp(value=5, name="add"),
+        MultiplyOp(factor=2, name="multiply"),
+    ]
+
+    _ = parent_op << sub_ops
+
+    assert len(parent_op.sub_ops) == 2, f"Expected 2 sub_ops, got {len(parent_op.sub_ops)}"
+    sub_op_names = [op.name for op in parent_op.sub_ops]
+    assert "add" in sub_op_names, "add not in sub_ops"
+    assert "multiply" in sub_op_names, "multiply not in sub_ops"
+    print("✓ test_add_sub_ops_list passed")
+
+
+async def test_mixed_composition_async():
+    """Test mixing >> and | operators in async mode."""
+    # (add_5 >> multiply_2) | (add_10 >> multiply_3)
+    seq1 = AddOp(value=5, name="add_5") >> MultiplyOp(factor=2, name="multiply_2")
+    seq2 = AddOp(value=10, name="add_10") >> MultiplyOp(factor=3, name="multiply_3")
+
+    composed = seq1 | seq2
+
+    await composed.call(number=10)
+
+    # Both sequences execute in parallel with shared context
+    # seq1: (10 + 5) * 2 = 30
+    # seq2: (30 + 10) * 3 = 120 (builds on seq1's result due to shared context)
+    # The exact result depends on execution order and timing
+    # With current implementation, result is 120
+    assert composed.context["number"] == 120, f"Expected 120, got {composed.context['number']}"
+    print("✓ test_mixed_composition_async passed")
+
+
+async def test_op_copy():
+    """Test operator copy functionality."""
+    original = AddOp(value=5, name="original")
+    copy_op = original.copy(name="copy")
+
+    assert copy_op.name == "copy", f"Expected name 'copy', got {copy_op.name}"
+    assert copy_op.value == 5, f"Expected value 5, got {copy_op.value}"
+    assert copy_op is not original, "Copy should be a different object"
+    print("✓ test_op_copy passed")
+
+
+async def test_input_mapping():
+    """Test input_mapping parameter."""
+    op = AddOp(
+        value=5,
+        name="add_5",
+        input_mapping={"x": "number"},  # Map x to number
+    )
+
+    await op.call(x=10)  # Input is 'x' not 'number'
+
+    assert op.context["number"] == 15, f"Expected number=15, got {op.context['number']}"
+    print("✓ test_input_mapping passed")
+
+
+async def test_output_mapping():
+    """Test output_mapping parameter."""
+    op = AddOp(
+        value=5,
+        name="add_5",
+        output_mapping={"number": "final_result"},  # Map number to final_result
+    )
+
+    await op.call(number=10)
+
+    assert op.context["number"] == 15, f"Expected number=15, got {op.context['number']}"
+    assert op.context["final_result"] == 15, f"Expected final_result=15, got {op.context['final_result']}"
+    print("✓ test_output_mapping passed")
+
+
+async def test_validation_missing_required():
+    """Test that missing required inputs raise an error."""
+    op = AddOp(value=5, name="add_5", raise_exception=True)
+
+    try:
+        await op.call()  # Missing 'number' field
+        assert False, "Should have raised ValueError for missing required input"
+    except ValueError as e:
+        assert "number" in str(e), f"Expected error about 'number', got: {e}"
+        print("✓ test_validation_missing_required passed")
+
+
+async def test_max_retries():
+    """Test max_retries parameter with failing operation."""
+
+    class FailingOp(BaseOp):
+        """An operation that always fails."""
+
+        def __init__(self, **kwargs):
+            super().__init__(**kwargs)
+            self.attempt_count = 0
+
+        def _build_tool_call(self) -> ToolCall:
+            return ToolCall(
+                **{
+                    "name": self.name,
+                    "description": "Always fails",
+                    "parameters": ToolAttr(**{"type": "object", "properties": {}}),
+                    "output": ToolAttr(
+                        **{
+                            "type": "object",
+                            "properties": {
+                                "result": ToolAttr(**{"type": "string", "description": "Result"}),
+                            },
+                        },
+                    ),
+                },
+            )
+
+        async def execute(self):
+            self.attempt_count += 1
+            raise RuntimeError(f"Attempt {self.attempt_count} failed")
+
+    op = FailingOp(max_retries=3, name="failing")
+
+    await op.call()
+
+    assert op.attempt_count == 3, f"Expected 3 attempts, got {op.attempt_count}"
+    print("✓ test_max_retries passed")
+
+
+async def async_main():
+    """Run all async tests."""
+    await test_basic_async_call()
+    await test_sequential_composition_async()
+    await test_parallel_composition_async()
+    await test_add_sub_ops_async()
+    await test_add_sub_ops_dict()
+    await test_add_sub_ops_list()
+    await test_mixed_composition_async()
+    await test_op_copy()
+    await test_input_mapping()
+    await test_output_mapping()
+    await test_validation_missing_required()
+    await test_max_retries()
+
+
+if __name__ == "__main__":
+    print("Running BaseOp composition tests...\n")
+
+    # Async tests
+    print("=== Asynchronous Tests ===")
+    asyncio.run(async_main())
+
+    print("\n" + "=" * 50)
+    print("All tests passed! ✓")
+    print("=" * 50)