diff --git a/libs/partners/openai/langchain_openai/chat_models/base.py b/libs/partners/openai/langchain_openai/chat_models/base.py
index 52dc6f9ba29..8fc35ea47d9 100644
--- a/libs/partners/openai/langchain_openai/chat_models/base.py
+++ b/libs/partners/openai/langchain_openai/chat_models/base.py
@@ -236,6 +236,26 @@ def _convert_dict_to_message(_dict: Mapping[str, Any]) -> BaseMessage:
     return ChatMessage(content=_dict.get("content", ""), role=role, id=id_)  # type: ignore[arg-type]
 
 
+def _sanitize_chat_completions_content(content: str | list[dict]) -> str | list[dict]:
+    """Sanitize content for chat/completions API.
+
+    For list content, filters text blocks to only keep 'type' and 'text' keys.
+    """
+    if isinstance(content, list):
+        sanitized = []
+        for block in content:
+            if (
+                isinstance(block, dict)
+                and block.get("type") == "text"
+                and "text" in block
+            ):
+                sanitized.append({"type": "text", "text": block["text"]})
+            else:
+                sanitized.append(block)
+        return sanitized
+    return content
+
+
 def _format_message_content(
     content: Any,
     api: Literal["chat/completions", "responses"] = "chat/completions",
@@ -368,7 +388,9 @@ def _convert_message_to_dict(
     elif isinstance(message, ToolMessage):
         message_dict["role"] = "tool"
         message_dict["tool_call_id"] = message.tool_call_id
-
+        message_dict["content"] = _sanitize_chat_completions_content(
+            message_dict["content"]
+        )
         supported_props = {"content", "role", "tool_call_id"}
         message_dict = {k: v for k, v in message_dict.items() if k in supported_props}
     else:
diff --git a/libs/partners/openai/tests/unit_tests/chat_models/test_base.py b/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
index fe87233572a..2297f428363 100644
--- a/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
+++ b/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
@@ -1264,6 +1264,23 @@ def test__get_request_payload() -> None:
     assert payload == expected
 
 
+def test_sanitize_chat_completions_text_blocks() -> None:
+    messages = [
+        ToolMessage(
+            content=[{"type": "text", "text": "foo", "id": "lc_abc123"}],
+            tool_call_id="def456",
+        ),
+    ]
+    payload = ChatOpenAI(model="gpt-5.2")._get_request_payload(messages)
+    assert payload["messages"] == [
+        {
+            "content": [{"type": "text", "text": "foo"}],
+            "role": "tool",
+            "tool_call_id": "def456",
+        }
+    ]
+
+
 def test_init_o1() -> None:
     with warnings.catch_warnings(record=True) as record:
         warnings.simplefilter("error")  # Treat warnings as errors