diff --git a/libs/partners/openai/langchain_openai/chat_models/_compat.py b/libs/partners/openai/langchain_openai/chat_models/_compat.py
index f1ac28392d4..86aff674295 100644
--- a/libs/partners/openai/langchain_openai/chat_models/_compat.py
+++ b/libs/partners/openai/langchain_openai/chat_models/_compat.py
@@ -485,12 +485,13 @@ def _implode_reasoning_blocks(blocks: list[dict[str, Any]]) -> Iterable[dict[str
     while i < n:
         block = blocks[i]
 
-        # Ordinary block – just yield a shallow copy
-        if block.get("type") != "reasoning":
+        # Skip non-reasoning blocks or blocks already in Responses format
+        if block.get("type") != "reasoning" or "summary" in block:
             yield dict(block)
             i += 1
             continue
-        elif "reasoning" not in block:
+        elif "reasoning" not in block and "summary" not in block:
+            # {"type": "reasoning", "id": "rs_..."}
             yield {**block, "summary": []}
             i += 1
             continue
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 d1c6b254614..f8120df7d3e 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
@@ -2563,7 +2563,7 @@ def test_convert_to_v1_from_chat_completions(
             ),
             AIMessage(
                 [
-                    {"type": "reasoning", "id": "abc123"},
+                    {"type": "reasoning", "id": "abc123", "summary": []},
                     {
                         "type": "reasoning",
                         "id": "abc234",