diff --git a/libs/core/langchain_core/messages/utils.py b/libs/core/langchain_core/messages/utils.py
index e39db43286b..b63c38045b8 100644
--- a/libs/core/langchain_core/messages/utils.py
+++ b/libs/core/langchain_core/messages/utils.py
@@ -938,7 +938,7 @@ def format_messages_as(
     messages: Union[MessageLikeRepresentation, Sequence[MessageLikeRepresentation]],
     *,
     format: Literal["openai", "anthropic"],
-    text: Literal["string", "block"],
+    text_format: Literal["string", "block"],
 ) -> Union[BaseMessage, List[BaseMessage]]:
     """Convert message contents into a standard format.
 
@@ -948,7 +948,7 @@ def format_messages_as(
         messages: Message-like object or iterable of objects whose contents are already
             in OpenAI, Anthropic, Bedrock Converse, or VertexAI formats.
         format: Format to convert message contents to.
-        text: How to format text contents. If ``text='string'``  then any string
+        text_format: How to format text contents. If ``text='string'``  then any string
             contents are left as strings. If a message has content blocks that are all
             of type 'text', these are joined with a newline to make a single string. If
             a message has content blocks and at least one isn't of type 'text', then
@@ -1059,9 +1059,9 @@ def format_messages_as(
         messages = [messages]
     messages = convert_to_messages(messages, copy=True)
     if format.lower() == "openai":
-        formatted = _format_messages_as_openai(messages, text=text)
+        formatted = _format_messages_as_openai(messages, text_format=text_format)
     elif format.lower() == "anthropic":
-        formatted = _format_messages_as_anthropic(messages, text=text)
+        formatted = _format_messages_as_anthropic(messages, text_format=text_format)
     else:
         raise ValueError(
             f"Unrecognized {format=}. Expected one of ('openai', 'anthropic')."
@@ -1073,21 +1073,21 @@ def format_messages_as(
 
 
 def _format_messages_as_openai(
-    messages: Sequence[BaseMessage], *, text: Literal["string", "block"]
+    messages: Sequence[BaseMessage], *, text_format: Literal["string", "block"]
 ) -> List[BaseMessage]:
     """Mutates messages so their contents match OpenAI messages API."""
     updated_messages: list = []
     for i, message in enumerate(messages):
         tool_messages: list = []
         if not message.content:
-            message.content = "" if text == "string" else []
+            message.content = "" if text_format == "string" else []
         elif isinstance(message.content, str):
-            if text == "string":
+            if text_format == "string":
                 pass
             else:
                 message.content = [{"type": "text", "text": message.content}]
         else:
-            if text == "string" and all(
+            if text_format == "string" and all(
                 isinstance(block, str) or block.get("type") == "text"
                 for block in message.content
             ):
@@ -1226,7 +1226,9 @@ def _format_messages_as_openai(
                         )
                         # Recurse to make sure tool message contents are OpenAI format.
                         tool_messages.extend(
-                            _format_messages_as_openai([tool_message], text=text)
+                            _format_messages_as_openai(
+                                [tool_message], text_format=text_format
+                            )
                         )
                     elif (block.get("type") == "json") or "json" in block:
                         if "json" not in block:
@@ -1292,7 +1294,7 @@ def _format_messages_as_openai(
                             f"Anthropic, Bedrock Converse, or VertexAI format. Full "
                             f"content block:\n\n{block}"
                         )
-                if text == "string" and not any(
+                if text_format == "string" and not any(
                     block["type"] != "text" for block in content
                 ):
                     message.content = "\n".join(block["text"] for block in content)
@@ -1306,7 +1308,7 @@ _OPTIONAL_ANTHROPIC_KEYS = ("cache_control", "is_error", "index")
 
 
 def _format_messages_as_anthropic(
-    messages: Sequence[BaseMessage], *, text: Literal["string", "block"]
+    messages: Sequence[BaseMessage], *, text_format: Literal["string", "block"]
 ) -> List[BaseMessage]:
     """Mutates messages so their contents match Anthropic messages API."""
     updated_messages: List = []
@@ -1328,9 +1330,9 @@ def _format_messages_as_anthropic(
                 updated_messages.append(HumanMessage([tool_result_block]))
             continue
         elif not message.content:
-            message.content = "" if text == "string" else []
+            message.content = "" if text_format == "string" else []
         elif isinstance(message.content, str):
-            if text == "string":
+            if text_format == "string":
                 pass
             else:
                 text_block: dict = {"type": "text", "text": message.content}
@@ -1338,7 +1340,7 @@ def _format_messages_as_anthropic(
                     text_block["index"] = 0
                 message.content = [text_block]
         else:
-            if text == "string" and all(
+            if text_format == "string" and all(
                 isinstance(block, str)
                 or (block.get("type") == "text" and "cache_control" not in block)
                 for block in message.content
diff --git a/libs/core/tests/unit_tests/messages/test_utils.py b/libs/core/tests/unit_tests/messages/test_utils.py
index b4047481b58..fd1761f1e7e 100644
--- a/libs/core/tests/unit_tests/messages/test_utils.py
+++ b/libs/core/tests/unit_tests/messages/test_utils.py
@@ -568,7 +568,7 @@ def create_base64_image(format: str = "jpeg") -> str:
 
 def test_format_messages_as_single_message() -> None:
     message = HumanMessage(content="Hello")
-    result = format_messages_as(message, format="openai", text="string")
+    result = format_messages_as(message, format="openai", text_format="string")
     assert isinstance(result, BaseMessage)
     assert result.content == "Hello"
 
@@ -579,7 +579,7 @@ def test_format_messages_as_multiple_messages() -> None:
         HumanMessage(content="Human message"),
         AIMessage(content="AI message"),
     ]
-    result = format_messages_as(messages, format="openai", text="string")
+    result = format_messages_as(messages, format="openai", text_format="string")
     assert isinstance(result, list)
     assert len(result) == 3
     assert all(isinstance(msg, BaseMessage) for msg in result)
@@ -602,7 +602,7 @@ def test_format_messages_as_openai_string() -> None:
             content=[{"type": "text", "text": "Hi"}, {"type": "text", "text": "there"}]
         ),
     ]
-    result = format_messages_as(messages, format="openai", text="string")
+    result = format_messages_as(messages, format="openai", text_format="string")
     assert [msg.content for msg in result] == ["Hello\nWorld", "Hi\nthere"]
 
 
@@ -611,7 +611,7 @@ def test_format_messages_as_openai_block() -> None:
         HumanMessage(content="Hello"),
         AIMessage(content="Hi there"),
     ]
-    result = format_messages_as(messages, format="openai", text="block")
+    result = format_messages_as(messages, format="openai", text_format="block")
     assert [msg.content for msg in result] == [
         [{"type": "text", "text": "Hello"}],
         [{"type": "text", "text": "Hi there"}],
@@ -630,7 +630,7 @@ def test_format_messages_as_anthropic_string() -> None:
             content=[{"type": "text", "text": "Hi"}, {"type": "text", "text": "there"}]
         ),
     ]
-    result = format_messages_as(messages, format="anthropic", text="string")
+    result = format_messages_as(messages, format="anthropic", text_format="string")
     assert [msg.content for msg in result] == ["Hello\nWorld", "Hi\nthere"]
 
 
@@ -639,7 +639,7 @@ def test_format_messages_as_anthropic_block() -> None:
         HumanMessage(content="Hello"),
         AIMessage(content="Hi there"),
     ]
-    result = format_messages_as(messages, format="anthropic", text="block")
+    result = format_messages_as(messages, format="anthropic", text_format="block")
     assert [msg.content for msg in result] == [
         [{"type": "text", "text": "Hello"}],
         [{"type": "text", "text": "Hi there"}],
@@ -649,7 +649,7 @@ def test_format_messages_as_anthropic_block() -> None:
 def test_format_messages_as_invalid_format() -> None:
     with pytest.raises(ValueError, match="Unrecognized format="):
         format_messages_as(
-            [HumanMessage(content="Hello")], format="invalid", text="string"
+            [HumanMessage(content="Hello")], format="invalid", text_format="string"
         )
 
 
@@ -663,7 +663,7 @@ def test_format_messages_as_openai_image() -> None:
             ]
         )
     ]
-    result = format_messages_as(messages, format="openai", text="block")
+    result = format_messages_as(messages, format="openai", text_format="block")
     assert result[0].content[1]["type"] == "image_url"
     assert result[0].content[1]["image_url"]["url"] == base64_image
 
@@ -678,7 +678,7 @@ def test_format_messages_as_anthropic_image() -> None:
             ]
         )
     ]
-    result = format_messages_as(messages, format="anthropic", text="block")
+    result = format_messages_as(messages, format="anthropic", text_format="block")
     assert result[0].content[1]["type"] == "image"
     assert result[0].content[1]["source"]["type"] == "base64"
     assert result[0].content[1]["source"]["media_type"] == "image/jpeg"
@@ -686,7 +686,7 @@ def test_format_messages_as_anthropic_image() -> None:
 
 def test_format_messages_as_tool_message() -> None:
     tool_message = ToolMessage(content="Tool result", tool_call_id="123")
-    result = format_messages_as([tool_message], format="openai", text="block")
+    result = format_messages_as([tool_message], format="openai", text_format="block")
     assert isinstance(result[0], ToolMessage)
     assert result[0].content == [{"type": "text", "text": "Tool result"}]
     assert result[0].tool_call_id == "123"
@@ -700,7 +700,7 @@ def test_format_messages_as_tool_use() -> None:
             ]
         )
     ]
-    result = format_messages_as(messages, format="openai", text="block")
+    result = format_messages_as(messages, format="openai", text_format="block")
     assert result[0].tool_calls[0]["id"] == "123"
     assert result[0].tool_calls[0]["name"] == "calculator"
     assert result[0].tool_calls[0]["args"] == "2+2"
@@ -709,7 +709,7 @@ def test_format_messages_as_tool_use() -> None:
 def test_format_messages_as_json() -> None:
     json_data = {"key": "value"}
     messages = [HumanMessage(content=[{"type": "json", "json": json_data}])]
-    result = format_messages_as(messages, format="openai", text="block")
+    result = format_messages_as(messages, format="openai", text_format="block")
     assert result[0].content[0]["type"] == "text"
     assert json.loads(result[0].content[0]["text"]) == json_data
 
@@ -725,7 +725,7 @@ def test_format_messages_as_guard_content() -> None:
             ]
         )
     ]
-    result = format_messages_as(messages, format="openai", text="block")
+    result = format_messages_as(messages, format="openai", text_format="block")
     assert result[0].content[0]["type"] == "text"
     assert result[0].content[0]["text"] == "Protected content"
 
@@ -738,7 +738,7 @@ def test_format_messages_as_vertexai_image() -> None:
             ]
         )
     ]
-    result = format_messages_as(messages, format="openai", text="block")
+    result = format_messages_as(messages, format="openai", text_format="block")
     assert result[0].content[0]["type"] == "image_url"
     assert (
         result[0].content[0]["image_url"]["url"]
@@ -749,20 +749,20 @@ def test_format_messages_as_vertexai_image() -> None:
 def test_format_messages_as_invalid_block() -> None:
     messages = [HumanMessage(content=[{"type": "invalid", "foo": "bar"}])]
     with pytest.raises(ValueError, match="Unrecognized content block"):
-        format_messages_as(messages, format="openai", text="block")
+        format_messages_as(messages, format="openai", text_format="block")
     with pytest.raises(ValueError, match="Unrecognized content block"):
-        format_messages_as(messages, format="anthropic", text="block")
+        format_messages_as(messages, format="anthropic", text_format="block")
 
 
 def test_format_messages_as_empty_message() -> None:
     result = format_messages_as(
-        HumanMessage(content=""), format="openai", text="string"
+        HumanMessage(content=""), format="openai", text_format="string"
     )
     assert result.content == ""
 
 
 def test_format_messages_as_empty_list() -> None:
-    result = format_messages_as([], format="openai", text="string")
+    result = format_messages_as([], format="openai", text_format="string")
     assert result == []
 
 
@@ -776,7 +776,7 @@ def test_format_messages_as_mixed_content_types() -> None:
             ]
         )
     ]
-    result = format_messages_as(messages, format="openai", text="block")
+    result = format_messages_as(messages, format="openai", text_format="block")
     assert len(result[0].content) == 3
     assert isinstance(result[0].content[0], dict)
     assert isinstance(result[0].content[1], dict)
@@ -790,7 +790,7 @@ def test_format_messages_as_anthropic_tool_calls() -> None:
             {"type": "tool_call", "name": "foo", "id": "1", "args": {"bar": "baz"}}
         ],
     )
-    result = format_messages_as(message, format="anthropic", text="string")
+    result = format_messages_as(message, format="anthropic", text_format="string")
     assert result.content == [
         {"type": "text", "text": "blah"},
         {"type": "tool_use", "id": "1", "name": "foo", "input": {"bar": "baz"}},
@@ -799,7 +799,7 @@ def test_format_messages_as_anthropic_tool_calls() -> None:
 
 
 def test_format_messages_as_declarative() -> None:
-    formatter = format_messages_as(format="openai", text="block")
+    formatter = format_messages_as(format="openai", text_format="block")
     base64_image = create_base64_image()
     messages = [
         HumanMessage(
@@ -996,7 +996,7 @@ def _stream_anthropic(input_: Any) -> Iterator:
 
 @pytest.mark.parametrize("stream", [_stream_oai, _stream_anthropic])
 def test_format_messages_openai_string_stream(stream: Callable) -> None:
-    formatter = format_messages_as(format="openai", text="string")
+    formatter = format_messages_as(format="openai", text_format="string")
 
     chain = RunnableLambda(stream) | formatter
     tool_call_idx = 1 if stream == _stream_anthropic else 0
@@ -1090,7 +1090,7 @@ def test_format_messages_openai_string_stream(stream: Callable) -> None:
 
 @pytest.mark.parametrize("stream", [_stream_oai, _stream_anthropic])
 def test_format_messages_openai_block_stream(stream: Callable) -> None:
-    formatter = format_messages_as(format="openai", text="block")
+    formatter = format_messages_as(format="openai", text_format="block")
 
     chain = RunnableLambda(stream) | formatter
     tool_call_idx = 1 if stream == _stream_anthropic else 0
@@ -1183,7 +1183,7 @@ def test_format_messages_openai_block_stream(stream: Callable) -> None:
 
 @pytest.mark.parametrize("stream", [_stream_oai, _stream_anthropic])
 def test_format_messages_anthropic_block_stream(stream: Callable) -> None:
-    formatter = format_messages_as(format="anthropic", text="block")
+    formatter = format_messages_as(format="anthropic", text_format="block")
 
     chain = RunnableLambda(stream) | formatter
     expected = [
@@ -1285,7 +1285,7 @@ def test_format_messages_anthropic_block_stream(stream: Callable) -> None:
 
 @pytest.mark.parametrize("stream", [_stream_oai, _stream_anthropic])
 def test_format_messages_anthropic_string_stream(stream: Callable) -> None:
-    formatter = format_messages_as(format="anthropic", text="string")
+    formatter = format_messages_as(format="anthropic", text_format="string")
 
     chain = RunnableLambda(stream) | formatter
     expected = [