From 33a6def76295f341fc499a53428b75efca1982af Mon Sep 17 00:00:00 2001
From: Mohammad Mohtashim <45242107+keenborder786@users.noreply.github.com>
Date: Mon, 29 Sep 2025 18:17:05 +0500
Subject: [PATCH] fix(core): Support of 'reasoning' type in
 'convert_to_openai_messages' (#33050)

---
 libs/core/langchain_core/messages/utils.py    |  2 +-
 .../tests/unit_tests/messages/test_utils.py   | 61 +++++++++++++++++++
 2 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/libs/core/langchain_core/messages/utils.py b/libs/core/langchain_core/messages/utils.py
index ea72ae06bad..d479d41e8bc 100644
--- a/libs/core/langchain_core/messages/utils.py
+++ b/libs/core/langchain_core/messages/utils.py
@@ -1385,7 +1385,7 @@ def convert_to_openai_messages(
                             },
                         }
                     )
-                elif block.get("type") == "thinking":
+                elif block.get("type") in ["thinking", "reasoning"]:
                     content.append(block)
                 else:
                     err = (
diff --git a/libs/core/tests/unit_tests/messages/test_utils.py b/libs/core/tests/unit_tests/messages/test_utils.py
index bedd518589e..5d324401de4 100644
--- a/libs/core/tests/unit_tests/messages/test_utils.py
+++ b/libs/core/tests/unit_tests/messages/test_utils.py
@@ -1484,3 +1484,64 @@ def test_get_buffer_string_with_empty_content() -> None:
     expected = "Human: \nAI: \nSystem: "
     actual = get_buffer_string(messages)
     assert actual == expected
+
+
+def test_convert_to_openai_messages_reasoning_content() -> None:
+    """Test convert_to_openai_messages with reasoning content blocks."""
+    # Test reasoning block with empty summary
+    msg = AIMessage(content=[{"type": "reasoning", "summary": []}])
+    result = convert_to_openai_messages(msg, text_format="block")
+    expected = {"role": "assistant", "content": [{"type": "reasoning", "summary": []}]}
+    assert result == expected
+
+    # Test reasoning block with summary content
+    msg_with_summary = AIMessage(
+        content=[
+            {
+                "type": "reasoning",
+                "summary": [
+                    {"type": "text", "text": "First thought"},
+                    {"type": "text", "text": "Second thought"},
+                ],
+            }
+        ]
+    )
+    result_with_summary = convert_to_openai_messages(
+        msg_with_summary, text_format="block"
+    )
+    expected_with_summary = {
+        "role": "assistant",
+        "content": [
+            {
+                "type": "reasoning",
+                "summary": [
+                    {"type": "text", "text": "First thought"},
+                    {"type": "text", "text": "Second thought"},
+                ],
+            }
+        ],
+    }
+    assert result_with_summary == expected_with_summary
+
+    # Test mixed content with reasoning and text
+    mixed_msg = AIMessage(
+        content=[
+            {"type": "text", "text": "Regular response"},
+            {
+                "type": "reasoning",
+                "summary": [{"type": "text", "text": "My reasoning process"}],
+            },
+        ]
+    )
+    mixed_result = convert_to_openai_messages(mixed_msg, text_format="block")
+    expected_mixed = {
+        "role": "assistant",
+        "content": [
+            {"type": "text", "text": "Regular response"},
+            {
+                "type": "reasoning",
+                "summary": [{"type": "text", "text": "My reasoning process"}],
+            },
+        ],
+    }
+    assert mixed_result == expected_mixed