diff --git a/tests/telemetry/test_trace.py b/tests/telemetry/test_trace.py
index 27cf2a35..cce8dad0 100644
--- a/tests/telemetry/test_trace.py
+++ b/tests/telemetry/test_trace.py
@@ -50,12 +50,13 @@ def _mock_span():
     return span
 
 
-def _make_part(text=None, function_call=None, function_response=None, inline_data=None):
+def _make_part(text=None, function_call=None, function_response=None, inline_data=None, thought=False):
     part = MagicMock()
     part.text = text
     part.function_call = function_call
     part.function_response = function_response
     part.inline_data = inline_data
+    part.thought = thought
     return part
 
 
@@ -229,6 +230,31 @@ def test_with_new_message(self, mock_get_span):
 
         span.set_attribute.assert_any_call("trpc.python.agent.runner.input", "hello\nworld")
 
+    @patch("trpc_agent_sdk.telemetry._trace.trace.get_current_span")
+    def test_with_thought_parts(self, mock_get_span):
+        span = _mock_span()
+        mock_get_span.return_value = span
+        ctx = _make_invocation_context()
+
+        parts = [
+            _make_part(text="thinking...", thought=True),
+            _make_part(text="final answer"),
+        ]
+        content = _make_content(parts=parts)
+
+        trace_runner(
+            app_name="app",
+            user_id="u",
+            session_id="s",
+            invocation_context=ctx,
+            new_message=content,
+        )
+
+        span.set_attribute.assert_any_call(
+            "trpc.python.agent.runner.input",
+            "<trace_think>thinking...</trace_think>\nfinal answer",
+        )
+
     @patch("trpc_agent_sdk.telemetry._trace.trace.get_current_span")
     def test_with_none_text_parts(self, mock_get_span):
         span = _mock_span()
@@ -544,6 +570,25 @@ def test_with_user_content(self, mock_get_span):
 
         span.set_attribute.assert_any_call("trpc.python.agent.agent.input", "hello\n agent")
 
+    @patch("trpc_agent_sdk.telemetry._trace.trace.get_current_span")
+    def test_with_thought_user_content(self, mock_get_span):
+        span = _mock_span()
+        mock_get_span.return_value = span
+
+        parts = [
+            _make_part(text="reasoning", thought=True),
+            _make_part(text="answer"),
+        ]
+        user_content = _make_content(parts=parts)
+        ctx = _make_invocation_context(user_content=user_content)
+
+        trace_agent(ctx)
+
+        span.set_attribute.assert_any_call(
+            "trpc.python.agent.agent.input",
+            "<trace_think>reasoning</trace_think>\nanswer",
+        )
+
     @patch("trpc_agent_sdk.telemetry._trace.trace.get_current_span")
     def test_without_user_content(self, mock_get_span):
         span = _mock_span()
diff --git a/trpc_agent_sdk/telemetry/_trace.py b/trpc_agent_sdk/telemetry/_trace.py
index 22ff2ad2..9c725906 100644
--- a/trpc_agent_sdk/telemetry/_trace.py
+++ b/trpc_agent_sdk/telemetry/_trace.py
@@ -62,6 +62,30 @@ def get_trpc_agent_span_name() -> str:
     return _trpc_agent_span_name
 
 
+def _join_parts_with_thought_tag(parts) -> str:
+    """Join part texts, wrapping thought parts in <trace_think> tags.
+
+    Parts with ``thought=True`` (model reasoning/thinking) are wrapped in
+    ``<trace_think>...</trace_think>`` tags so downstream consumers (e.g.
+    zhiyan-llm exporter) can distinguish and optionally strip them.
+
+    Args:
+        parts: A sequence of Part objects with ``text`` and optional
+            ``thought`` attributes.
+
+    Returns:
+        The joined text string with thought parts tagged.
+    """
+    result = []
+    for part in parts:
+        text = part.text or ""
+        if getattr(part, "thought", False):
+            result.append(f"<trace_think>{text}</trace_think>")
+        else:
+            result.append(text)
+    return "\n".join(result)
+
+
 def _safe_json_serialize(obj) -> str:
     """Convert any Python object to a JSON-serializable type or string.
 
@@ -116,11 +140,11 @@ def trace_runner(
     span.set_attribute(f"{_trpc_agent_span_name}.runner.session_id", session_id)
     input_str = ""
     if new_message and new_message.parts:
-        input_str = "\n".join([part.text or "" for part in new_message.parts])
+        input_str = _join_parts_with_thought_tag(new_message.parts)
     span.set_attribute(f"{_trpc_agent_span_name}.runner.input", input_str)
     output_str = ""
     if last_event and last_event.content and last_event.content.parts:
-        output_str = "\n".join([part.text or "" for part in last_event.content.parts])
+        output_str = _join_parts_with_thought_tag(last_event.content.parts)
     span.set_attribute(f"{_trpc_agent_span_name}.runner.output", output_str)
 
     # Set state attributes for begin and end
@@ -181,7 +205,7 @@ def trace_cancellation(
     # Input (prefixed with [CANCELLED] marker)
     input_str = ""
     if new_message and new_message.parts:
-        input_str += "\n".join([part.text or "" for part in new_message.parts])
+        input_str += _join_parts_with_thought_tag(new_message.parts)
     span.set_attribute(f"{_trpc_agent_span_name}.runner.input", input_str)
 
     # Output (prefixed with [CANCELLED] marker, includes partial text or last event)
@@ -189,7 +213,7 @@ def trace_cancellation(
     if partial_text:
         output_str += partial_text
     elif last_event and last_event.content and last_event.content.parts:
-        output_str += "\n".join([part.text or "" for part in last_event.content.parts])
+        output_str += _join_parts_with_thought_tag(last_event.content.parts)
     span.set_attribute(f"{_trpc_agent_span_name}.runner.output", output_str)
 
     # Cancellation-specific attributes
@@ -245,11 +269,14 @@ def trace_agent(
         for content in override_messages:
             if content and content.parts:
                 for part in content.parts:
-                    if part.text and not part.thought:
-                        text_parts.append(part.text)
+                    if part.text:
+                        if getattr(part, "thought", False):
+                            text_parts.append(f"<trace_think>{part.text}</trace_think>")
+                        else:
+                            text_parts.append(part.text)
         input_str = "\n".join(text_parts)
     elif invocation_context.user_content and invocation_context.user_content.parts:
-        input_str = "\n".join([part.text or "" for part in invocation_context.user_content.parts])
+        input_str = _join_parts_with_thought_tag(invocation_context.user_content.parts)
     span.set_attribute(f"{_trpc_agent_span_name}.agent.input", input_str)
 
     span.set_attribute(f"{_trpc_agent_span_name}.agent.output", agent_action)