diff --git a/lightrag/lightrag.py b/lightrag/lightrag.py
index 08f0e6d9..62aaf17d 100644
--- a/lightrag/lightrag.py
+++ b/lightrag/lightrag.py
@@ -2108,6 +2108,7 @@ class LightRAG:
                 query.strip(),
                 system_prompt=system_prompt,
                 history_messages=param.conversation_history,
+                enable_cot=True,
                 stream=param.stream,
             )
         else:
diff --git a/lightrag/llm/anthropic.py b/lightrag/llm/anthropic.py
index 98a997d5..fe18300c 100644
--- a/lightrag/llm/anthropic.py
+++ b/lightrag/llm/anthropic.py
@@ -59,12 +59,17 @@ async def anthropic_complete_if_cache(
     prompt: str,
     system_prompt: str | None = None,
     history_messages: list[dict[str, Any]] | None = None,
+    enable_cot: bool = False,
     base_url: str | None = None,
     api_key: str | None = None,
     **kwargs: Any,
 ) -> Union[str, AsyncIterator[str]]:
     if history_messages is None:
         history_messages = []
+    if enable_cot:
+        logger.debug(
+            "enable_cot=True is not supported for the Anthropic API and will be ignored."
+        )
     if not api_key:
         api_key = os.environ.get("ANTHROPIC_API_KEY")
 
@@ -150,6 +155,7 @@ async def anthropic_complete(
     prompt: str,
     system_prompt: str | None = None,
     history_messages: list[dict[str, Any]] | None = None,
+    enable_cot: bool = False,
     **kwargs: Any,
 ) -> Union[str, AsyncIterator[str]]:
     if history_messages is None:
@@ -160,6 +166,7 @@ async def anthropic_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         **kwargs,
     )
 
@@ -169,6 +176,7 @@ async def claude_3_opus_complete(
     prompt: str,
     system_prompt: str | None = None,
     history_messages: list[dict[str, Any]] | None = None,
+    enable_cot: bool = False,
     **kwargs: Any,
 ) -> Union[str, AsyncIterator[str]]:
     if history_messages is None:
@@ -178,6 +186,7 @@ async def claude_3_opus_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         **kwargs,
     )
 
@@ -187,6 +196,7 @@ async def claude_3_sonnet_complete(
     prompt: str,
     system_prompt: str | None = None,
     history_messages: list[dict[str, Any]] | None = None,
+    enable_cot: bool = False,
     **kwargs: Any,
 ) -> Union[str, AsyncIterator[str]]:
     if history_messages is None:
@@ -196,6 +206,7 @@ async def claude_3_sonnet_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         **kwargs,
     )
 
@@ -205,6 +216,7 @@ async def claude_3_haiku_complete(
     prompt: str,
     system_prompt: str | None = None,
     history_messages: list[dict[str, Any]] | None = None,
+    enable_cot: bool = False,
     **kwargs: Any,
 ) -> Union[str, AsyncIterator[str]]:
     if history_messages is None:
@@ -214,6 +226,7 @@ async def claude_3_haiku_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         **kwargs,
     )
 
diff --git a/lightrag/llm/azure_openai.py b/lightrag/llm/azure_openai.py
index 0ede0824..824ff088 100644
--- a/lightrag/llm/azure_openai.py
+++ b/lightrag/llm/azure_openai.py
@@ -24,6 +24,7 @@ from tenacity import (
 from lightrag.utils import (
     wrap_embedding_func_with_attrs,
     safe_unicode_decode,
+    logger,
 )
 
 import numpy as np
@@ -41,11 +42,16 @@ async def azure_openai_complete_if_cache(
     prompt,
     system_prompt: str | None = None,
     history_messages: Iterable[ChatCompletionMessageParam] | None = None,
+    enable_cot: bool = False,
     base_url: str | None = None,
     api_key: str | None = None,
     api_version: str | None = None,
     **kwargs,
 ):
+    if enable_cot:
+        logger.debug(
+            "enable_cot=True is not supported for the Azure OpenAI API and will be ignored."
+        )
     deployment = os.getenv("AZURE_OPENAI_DEPLOYMENT") or model or os.getenv("LLM_MODEL")
     base_url = (
         base_url or os.getenv("AZURE_OPENAI_ENDPOINT") or os.getenv("LLM_BINDING_HOST")
diff --git a/lightrag/llm/bedrock.py b/lightrag/llm/bedrock.py
index 69d00e2d..16737341 100644
--- a/lightrag/llm/bedrock.py
+++ b/lightrag/llm/bedrock.py
@@ -44,11 +44,18 @@ async def bedrock_complete_if_cache(
     prompt,
     system_prompt=None,
     history_messages=[],
+    enable_cot: bool = False,
     aws_access_key_id=None,
     aws_secret_access_key=None,
     aws_session_token=None,
     **kwargs,
 ) -> Union[str, AsyncIterator[str]]:
+    if enable_cot:
+        import logging
+
+        logging.debug(
+            "enable_cot=True is not supported for Bedrock and will be ignored."
+        )
     # Respect existing env; only set if a non-empty value is available
     access_key = os.environ.get("AWS_ACCESS_KEY_ID") or aws_access_key_id
     secret_key = os.environ.get("AWS_SECRET_ACCESS_KEY") or aws_secret_access_key
diff --git a/lightrag/llm/hf.py b/lightrag/llm/hf.py
index 7adf1570..c33b1c7f 100644
--- a/lightrag/llm/hf.py
+++ b/lightrag/llm/hf.py
@@ -56,8 +56,15 @@ async def hf_model_if_cache(
     prompt,
     system_prompt=None,
     history_messages=[],
+    enable_cot: bool = False,
     **kwargs,
 ) -> str:
+    if enable_cot:
+        from lightrag.utils import logger
+
+        logger.debug(
+            "enable_cot=True is not supported for Hugging Face local models and will be ignored."
+        )
     model_name = model
     hf_model, hf_tokenizer = initialize_hf_model(model_name)
     messages = []
@@ -114,7 +121,12 @@ async def hf_model_if_cache(
 
 
 async def hf_model_complete(
-    prompt, system_prompt=None, history_messages=[], keyword_extraction=False, **kwargs
+    prompt,
+    system_prompt=None,
+    history_messages=[],
+    keyword_extraction=False,
+    enable_cot: bool = False,
+    **kwargs,
 ) -> str:
     kwargs.pop("keyword_extraction", None)
     model_name = kwargs["hashing_kv"].global_config["llm_model_name"]
@@ -123,6 +135,7 @@ async def hf_model_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         **kwargs,
     )
     return result
diff --git a/lightrag/llm/llama_index_impl.py b/lightrag/llm/llama_index_impl.py
index 2e50e33e..38ec7cd1 100644
--- a/lightrag/llm/llama_index_impl.py
+++ b/lightrag/llm/llama_index_impl.py
@@ -94,9 +94,14 @@ async def llama_index_complete_if_cache(
     prompt: str,
     system_prompt: Optional[str] = None,
     history_messages: List[dict] = [],
+    enable_cot: bool = False,
     chat_kwargs={},
 ) -> str:
     """Complete the prompt using LlamaIndex."""
+    if enable_cot:
+        logger.debug(
+            "enable_cot=True is not supported for LlamaIndex implementation and will be ignored."
+        )
     try:
         # Format messages for chat
         formatted_messages = []
@@ -138,6 +143,7 @@ async def llama_index_complete(
     prompt,
     system_prompt=None,
     history_messages=None,
+    enable_cot: bool = False,
     keyword_extraction=False,
     settings: LlamaIndexSettings = None,
     **kwargs,
@@ -162,6 +168,7 @@ async def llama_index_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         **kwargs,
     )
     return result
diff --git a/lightrag/llm/lmdeploy.py b/lightrag/llm/lmdeploy.py
index 50e60cd6..8916b0fd 100644
--- a/lightrag/llm/lmdeploy.py
+++ b/lightrag/llm/lmdeploy.py
@@ -56,6 +56,7 @@ async def lmdeploy_model_if_cache(
     prompt,
     system_prompt=None,
     history_messages=[],
+    enable_cot: bool = False,
     chat_template=None,
     model_format="hf",
     quant_policy=0,
@@ -89,6 +90,12 @@ async def lmdeploy_model_if_cache(
         do_sample (bool): Whether or not to use sampling, use greedy decoding otherwise.
             Default to be False, which means greedy decoding will be applied.
     """
+    if enable_cot:
+        from lightrag.utils import logger
+
+        logger.debug(
+            "enable_cot=True is not supported for lmdeploy and will be ignored."
+        )
     try:
         import lmdeploy
         from lmdeploy import version_info, GenerationConfig
diff --git a/lightrag/llm/lollms.py b/lightrag/llm/lollms.py
index 39b64ce3..9274dbfc 100644
--- a/lightrag/llm/lollms.py
+++ b/lightrag/llm/lollms.py
@@ -39,10 +39,15 @@ async def lollms_model_if_cache(
     prompt,
     system_prompt=None,
     history_messages=[],
+    enable_cot: bool = False,
     base_url="http://localhost:9600",
     **kwargs,
 ) -> Union[str, AsyncIterator[str]]:
     """Client implementation for lollms generation."""
+    if enable_cot:
+        from lightrag.utils import logger
+
+        logger.debug("enable_cot=True is not supported for lollms and will be ignored.")
 
     stream = True if kwargs.get("stream") else False
     api_key = kwargs.pop("api_key", None)
@@ -98,7 +103,12 @@ async def lollms_model_if_cache(
 
 
 async def lollms_model_complete(
-    prompt, system_prompt=None, history_messages=[], keyword_extraction=False, **kwargs
+    prompt,
+    system_prompt=None,
+    history_messages=[],
+    enable_cot: bool = False,
+    keyword_extraction=False,
+    **kwargs,
 ) -> Union[str, AsyncIterator[str]]:
     """Complete function for lollms model generation."""
 
@@ -119,6 +129,7 @@ async def lollms_model_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         **kwargs,
     )
 
diff --git a/lightrag/llm/ollama.py b/lightrag/llm/ollama.py
index 6423fa90..c6fb46fc 100644
--- a/lightrag/llm/ollama.py
+++ b/lightrag/llm/ollama.py
@@ -43,8 +43,11 @@ async def _ollama_model_if_cache(
     prompt,
     system_prompt=None,
     history_messages=[],
+    enable_cot: bool = False,
     **kwargs,
 ) -> Union[str, AsyncIterator[str]]:
+    if enable_cot:
+        logger.debug("enable_cot=True is not supported for ollama and will be ignored.")
     stream = True if kwargs.get("stream") else False
 
     kwargs.pop("max_tokens", None)
@@ -123,7 +126,12 @@ async def _ollama_model_if_cache(
 
 
 async def ollama_model_complete(
-    prompt, system_prompt=None, history_messages=[], keyword_extraction=False, **kwargs
+    prompt,
+    system_prompt=None,
+    history_messages=[],
+    enable_cot: bool = False,
+    keyword_extraction=False,
+    **kwargs,
 ) -> Union[str, AsyncIterator[str]]:
     keyword_extraction = kwargs.pop("keyword_extraction", None)
     if keyword_extraction:
@@ -134,6 +142,7 @@ async def ollama_model_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         **kwargs,
     )
 
diff --git a/lightrag/llm/openai.py b/lightrag/llm/openai.py
index dd377862..6d486afc 100644
--- a/lightrag/llm/openai.py
+++ b/lightrag/llm/openai.py
@@ -111,12 +111,29 @@ async def openai_complete_if_cache(
     prompt: str,
     system_prompt: str | None = None,
     history_messages: list[dict[str, Any]] | None = None,
+    enable_cot: bool = False,
     base_url: str | None = None,
     api_key: str | None = None,
     token_tracker: Any | None = None,
     **kwargs: Any,
 ) -> str:
-    """Complete a prompt using OpenAI's API with caching support.
+    """Complete a prompt using OpenAI's API with caching support and Chain of Thought (COT) integration.
+
+    This function supports automatic integration of reasoning content (思维链) from models that provide
+    Chain of Thought capabilities. The reasoning content is seamlessly integrated into the response
+    using <think>...</think> tags.
+
+    Note on `reasoning_content`: This feature relies on a Deepseek Style `reasoning_content`
+    in the API response, which may be provided by OpenAI-compatible endpoints that support
+    Chain of Thought.
+
+    COT Integration Rules:
+    1. COT content is accepted only when regular content is empty and `reasoning_content` has content.
+    2. COT processing stops when regular content becomes available.
+    3. If both `content` and `reasoning_content` are present simultaneously, reasoning is ignored.
+    4. If both fields have content from the start, COT is never activated.
+    5. For streaming: COT content is inserted into the content stream with <think> tags.
+    6. For non-streaming: COT content is prepended to regular content with <think> tags.
 
     Args:
         model: The OpenAI model to use.
@@ -125,6 +142,8 @@ async def openai_complete_if_cache(
         history_messages: Optional list of previous messages in the conversation.
         base_url: Optional base URL for the OpenAI API.
         api_key: Optional OpenAI API key. If None, uses the OPENAI_API_KEY environment variable.
+        token_tracker: Optional token usage tracker for monitoring API usage.
+        enable_cot: Whether to enable Chain of Thought (COT) processing. Default is False.
         **kwargs: Additional keyword arguments to pass to the OpenAI API.
             Special kwargs:
             - openai_client_configs: Dict of configuration options for the AsyncOpenAI client.
@@ -134,7 +153,8 @@ async def openai_complete_if_cache(
             - keyword_extraction: Will be removed from kwargs before passing to OpenAI.
 
     Returns:
-        The completed text or an async iterator of text chunks if streaming.
+        The completed text (with integrated COT content if available) or an async iterator
+        of text chunks if streaming. COT content is wrapped in <think>...</think> tags.
 
     Raises:
         InvalidResponseError: If the response from OpenAI is invalid or empty.
@@ -217,6 +237,11 @@ async def openai_complete_if_cache(
             iteration_started = False
             final_chunk_usage = None
 
+            # COT (Chain of Thought) state tracking
+            cot_active = False
+            cot_started = False
+            initial_content_seen = False
+
             try:
                 iteration_started = True
                 async for chunk in response:
@@ -232,20 +257,65 @@ async def openai_complete_if_cache(
                         logger.warning(f"Received chunk without choices: {chunk}")
                         continue
 
-                    # Check if delta exists and has content
-                    if not hasattr(chunk.choices[0], "delta") or not hasattr(
-                        chunk.choices[0].delta, "content"
-                    ):
+                    # Check if delta exists
+                    if not hasattr(chunk.choices[0], "delta"):
                         # This might be the final chunk, continue to check for usage
                         continue
 
-                    content = chunk.choices[0].delta.content
-                    if content is None:
-                        continue
-                    if r"\u" in content:
-                        content = safe_unicode_decode(content.encode("utf-8"))
+                    delta = chunk.choices[0].delta
+                    content = getattr(delta, "content", None)
+                    reasoning_content = getattr(delta, "reasoning_content", None)
 
-                    yield content
+                    # Handle COT logic for streaming (only if enabled)
+                    if enable_cot:
+                        if content is not None and content != "":
+                            # Regular content is present
+                            if not initial_content_seen:
+                                initial_content_seen = True
+                                # If both content and reasoning_content are present initially, don't start COT
+                                if (
+                                    reasoning_content is not None
+                                    and reasoning_content != ""
+                                ):
+                                    cot_active = False
+                                    cot_started = False
+
+                            # If COT was active, end it
+                            if cot_active:
+                                yield "</think>"
+                                cot_active = False
+
+                            # Process regular content
+                            if r"\u" in content:
+                                content = safe_unicode_decode(content.encode("utf-8"))
+                            yield content
+
+                        elif reasoning_content is not None and reasoning_content != "":
+                            # Only reasoning content is present
+                            if not initial_content_seen and not cot_started:
+                                # Start COT if we haven't seen initial content yet
+                                if not cot_active:
+                                    yield "<think>"
+                                    cot_active = True
+                                    cot_started = True
+
+                            # Process reasoning content if COT is active
+                            if cot_active:
+                                if r"\u" in reasoning_content:
+                                    reasoning_content = safe_unicode_decode(
+                                        reasoning_content.encode("utf-8")
+                                    )
+                                yield reasoning_content
+                    else:
+                        # COT disabled, only process regular content
+                        if content is not None and content != "":
+                            if r"\u" in content:
+                                content = safe_unicode_decode(content.encode("utf-8"))
+                            yield content
+
+                    # If neither content nor reasoning_content, continue to next chunk
+                    if content is None and reasoning_content is None:
+                        continue
 
                 # After streaming is complete, track token usage
                 if token_tracker and final_chunk_usage:
@@ -313,21 +383,56 @@ async def openai_complete_if_cache(
                 not response
                 or not response.choices
                 or not hasattr(response.choices[0], "message")
-                or not hasattr(response.choices[0].message, "content")
             ):
                 logger.error("Invalid response from OpenAI API")
                 await openai_async_client.close()  # Ensure client is closed
                 raise InvalidResponseError("Invalid response from OpenAI API")
 
-            content = response.choices[0].message.content
+            message = response.choices[0].message
+            content = getattr(message, "content", None)
+            reasoning_content = getattr(message, "reasoning_content", None)
 
-            if not content or content.strip() == "":
+            # Handle COT logic for non-streaming responses (only if enabled)
+            final_content = ""
+
+            if enable_cot:
+                # Check if we should include reasoning content
+                should_include_reasoning = False
+                if reasoning_content and reasoning_content.strip():
+                    if not content or content.strip() == "":
+                        # Case 1: Only reasoning content, should include COT
+                        should_include_reasoning = True
+                        final_content = (
+                            content or ""
+                        )  # Use empty string if content is None
+                    else:
+                        # Case 3: Both content and reasoning_content present, ignore reasoning
+                        should_include_reasoning = False
+                        final_content = content
+                else:
+                    # No reasoning content, use regular content
+                    final_content = content or ""
+
+                # Apply COT wrapping if needed
+                if should_include_reasoning:
+                    if r"\u" in reasoning_content:
+                        reasoning_content = safe_unicode_decode(
+                            reasoning_content.encode("utf-8")
+                        )
+                    final_content = f"<think>{reasoning_content}</think>{final_content}"
+            else:
+                # COT disabled, only use regular content
+                final_content = content or ""
+
+            # Validate final content
+            if not final_content or final_content.strip() == "":
                 logger.error("Received empty content from OpenAI API")
                 await openai_async_client.close()  # Ensure client is closed
                 raise InvalidResponseError("Received empty content from OpenAI API")
 
-            if r"\u" in content:
-                content = safe_unicode_decode(content.encode("utf-8"))
+            # Apply Unicode decoding to final content if needed
+            if r"\u" in final_content:
+                final_content = safe_unicode_decode(final_content.encode("utf-8"))
 
             if token_tracker and hasattr(response, "usage"):
                 token_counts = {
@@ -339,10 +444,10 @@ async def openai_complete_if_cache(
                 }
                 token_tracker.add_usage(token_counts)
 
-            logger.debug(f"Response content len: {len(content)}")
+            logger.debug(f"Response content len: {len(final_content)}")
             verbose_debug(f"Response: {response}")
 
-            return content
+            return final_content
         finally:
             # Ensure client is closed in all cases for non-streaming responses
             await openai_async_client.close()
@@ -374,6 +479,7 @@ async def gpt_4o_complete(
     prompt,
     system_prompt=None,
     history_messages=None,
+    enable_cot: bool = False,
     keyword_extraction=False,
     **kwargs,
 ) -> str:
@@ -387,6 +493,7 @@ async def gpt_4o_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         **kwargs,
     )
 
@@ -395,6 +502,7 @@ async def gpt_4o_mini_complete(
     prompt,
     system_prompt=None,
     history_messages=None,
+    enable_cot: bool = False,
     keyword_extraction=False,
     **kwargs,
 ) -> str:
@@ -408,6 +516,7 @@ async def gpt_4o_mini_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         **kwargs,
     )
 
@@ -416,6 +525,7 @@ async def nvidia_openai_complete(
     prompt,
     system_prompt=None,
     history_messages=None,
+    enable_cot: bool = False,
     keyword_extraction=False,
     **kwargs,
 ) -> str:
@@ -427,6 +537,7 @@ async def nvidia_openai_complete(
         prompt,
         system_prompt=system_prompt,
         history_messages=history_messages,
+        enable_cot=enable_cot,
         base_url="https://integrate.api.nvidia.com/v1",
         **kwargs,
     )
diff --git a/lightrag/llm/zhipu.py b/lightrag/llm/zhipu.py
index c9d1253e..d90f3cc1 100644
--- a/lightrag/llm/zhipu.py
+++ b/lightrag/llm/zhipu.py
@@ -49,8 +49,13 @@ async def zhipu_complete_if_cache(
     api_key: Optional[str] = None,
     system_prompt: Optional[str] = None,
     history_messages: List[Dict[str, str]] = [],
+    enable_cot: bool = False,
     **kwargs,
 ) -> str:
+    if enable_cot:
+        logger.debug(
+            "enable_cot=True is not supported for ZhipuAI and will be ignored."
+        )
     # dynamically load ZhipuAI
     try:
         from zhipuai import ZhipuAI
@@ -91,7 +96,12 @@ async def zhipu_complete_if_cache(
 
 
 async def zhipu_complete(
-    prompt, system_prompt=None, history_messages=[], keyword_extraction=False, **kwargs
+    prompt,
+    system_prompt=None,
+    history_messages=[],
+    keyword_extraction=False,
+    enable_cot: bool = False,
+    **kwargs,
 ):
     # Pop keyword_extraction from kwargs to avoid passing it to zhipu_complete_if_cache
     keyword_extraction = kwargs.pop("keyword_extraction", None)
@@ -122,6 +132,7 @@ async def zhipu_complete(
                 prompt=prompt,
                 system_prompt=system_prompt,
                 history_messages=history_messages,
+                enable_cot=enable_cot,
                 **kwargs,
             )
 
@@ -163,6 +174,7 @@ async def zhipu_complete(
             prompt=prompt,
             system_prompt=system_prompt,
             history_messages=history_messages,
+            enable_cot=enable_cot,
             **kwargs,
         )
 
diff --git a/lightrag/operate.py b/lightrag/operate.py
index 162a9bc4..6635ef94 100644
--- a/lightrag/operate.py
+++ b/lightrag/operate.py
@@ -2213,6 +2213,7 @@ async def kg_query(
         query,
         system_prompt=sys_prompt,
         stream=query_param.stream,
+        enable_cot=True,
     )
     if isinstance(response, str) and len(response) > len(sys_prompt):
         response = (
@@ -4070,6 +4071,7 @@ async def naive_query(
         query,
         system_prompt=sys_prompt,
         stream=query_param.stream,
+        enable_cot=True,
     )
 
     if isinstance(response, str) and len(response) > len(sys_prompt):