diff --git a/libs/core/langchain_core/document_loaders/langsmith.py b/libs/core/langchain_core/document_loaders/langsmith.py
index 232da98ccf7..9da48851d06 100644
--- a/libs/core/langchain_core/document_loaders/langsmith.py
+++ b/libs/core/langchain_core/document_loaders/langsmith.py
@@ -73,7 +73,7 @@ class LangSmithLoader(BaseLoader):
             inline_s3_urls: Whether to inline S3 URLs. Defaults to True.
             offset: The offset to start from. Defaults to 0.
             limit: The maximum number of examples to return.
-            filter: A structured fileter string to apply to the examples.
+            filter: A structured filter string to apply to the examples.
             client: LangSmith Client. If not provided will be initialized from below args.
             client_kwargs: Keyword args to pass to LangSmith client init. Should only be
                 specified if ``client`` isn't.
diff --git a/libs/core/langchain_core/messages/utils.py b/libs/core/langchain_core/messages/utils.py
index c7d4d58a149..6f88fcbcf79 100644
--- a/libs/core/langchain_core/messages/utils.py
+++ b/libs/core/langchain_core/messages/utils.py
@@ -443,6 +443,8 @@ def filter_messages(
 @_runnable_support
 def merge_message_runs(
     messages: Union[Iterable[MessageLikeRepresentation], PromptValue],
+    *,
+    chunk_separator: str = "\n",
 ) -> List[BaseMessage]:
     """Merge consecutive Messages of the same type.
 
@@ -451,13 +453,16 @@ def merge_message_runs(
 
     Args:
         messages: Sequence Message-like objects to merge.
+        chunk_separator: Specify the string to be inserted between message chunks.
+        Default is "\n".
 
     Returns:
         List of BaseMessages with consecutive runs of message types merged into single
-        messages. If two messages being merged both have string contents, the merged
-        content is a concatenation of the two strings with a new-line separator. If at
-        least one of the messages has a list of content blocks, the merged content is a
-        list of content blocks.
+        messages. By default, if two messages being merged both have string contents,
+        the merged content is a concatenation of the two strings with a new-line separator.
+        The separator inserted between message chunks can be controlled by specifying
+        any string with ``chunk_separator``. If at least one of the messages has a list of
+        content blocks, the merged content is a list of content blocks.
 
     Example:
         .. code-block:: python
@@ -527,7 +532,7 @@ def merge_message_runs(
                 and last_chunk.content
                 and curr_chunk.content
             ):
-                last_chunk.content += "\n"
+                last_chunk.content += chunk_separator
             merged.append(_chunk_to_msg(last_chunk + curr_chunk))
     return merged
 
@@ -799,7 +804,7 @@ def trim_messages(
             list_token_counter = token_counter  # type: ignore[assignment]
     else:
         raise ValueError(
-            f"'token_counter' expected ot be a model that implements "
+            f"'token_counter' expected to be a model that implements "
             f"'get_num_tokens_from_messages()' or a function. Received object of type "
             f"{type(token_counter)}."
         )
diff --git a/libs/core/tests/unit_tests/messages/test_utils.py b/libs/core/tests/unit_tests/messages/test_utils.py
index 3f25e02fb23..56b8c0df7be 100644
--- a/libs/core/tests/unit_tests/messages/test_utils.py
+++ b/libs/core/tests/unit_tests/messages/test_utils.py
@@ -30,6 +30,30 @@ def test_merge_message_runs_str(msg_cls: Type[BaseMessage]) -> None:
     assert messages == messages_copy
 
 
+@pytest.mark.parametrize("msg_cls", [HumanMessage, AIMessage, SystemMessage])
+def test_merge_message_runs_str_with_specified_separator(
+    msg_cls: Type[BaseMessage],
+) -> None:
+    messages = [msg_cls("foo"), msg_cls("bar"), msg_cls("baz")]
+    messages_copy = [m.copy(deep=True) for m in messages]
+    expected = [msg_cls("foo<sep>bar<sep>baz")]
+    actual = merge_message_runs(messages, chunk_separator="<sep>")
+    assert actual == expected
+    assert messages == messages_copy
+
+
+@pytest.mark.parametrize("msg_cls", [HumanMessage, AIMessage, SystemMessage])
+def test_merge_message_runs_str_without_separator(
+    msg_cls: Type[BaseMessage],
+) -> None:
+    messages = [msg_cls("foo"), msg_cls("bar"), msg_cls("baz")]
+    messages_copy = [m.copy(deep=True) for m in messages]
+    expected = [msg_cls("foobarbaz")]
+    actual = merge_message_runs(messages, chunk_separator="")
+    assert actual == expected
+    assert messages == messages_copy
+
+
 def test_merge_message_runs_content() -> None:
     messages = [
         AIMessage("foo", id="1"),