From b00646d88273f13feedc26b6167c96c6effc279d Mon Sep 17 00:00:00 2001
From: Eugene Yurtsev <eyurtsev@gmail.com>
Date: Thu, 16 Apr 2026 15:17:20 -0400
Subject: [PATCH] chore(core): keep checkpoint_ns behavior in streaming
 metadata for backwards compat (#36828)

minor buglet
---
 libs/core/langchain_core/runnables/config.py  | 16 +++++++++-----
 .../tests/unit_tests/runnables/test_config.py | 21 ++++++++++++++++++-
 2 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/libs/core/langchain_core/runnables/config.py b/libs/core/langchain_core/runnables/config.py
index 5bae0488370..d94d049fc52 100644
--- a/libs/core/langchain_core/runnables/config.py
+++ b/libs/core/langchain_core/runnables/config.py
@@ -286,11 +286,17 @@ def ensure_config(config: RunnableConfig | None = None) -> RunnableConfig:
         for k, v in config.items():
             if k not in CONFIG_KEYS and v is not None:
                 empty["configurable"][k] = v
-    if (
-        isinstance(model := empty.get("configurable", {}).get("model"), str)
-        and "model" not in empty["metadata"]
-    ):
-        empty["metadata"]["model"] = model
+    for configurable_key in ("model", "checkpoint_ns"):
+        if (
+            isinstance(
+                configurable_value := empty.get("configurable", {}).get(
+                    configurable_key
+                ),
+                str,
+            )
+            and configurable_key not in empty["metadata"]
+        ):
+            empty["metadata"][configurable_key] = configurable_value
     return empty
 
 
diff --git a/libs/core/tests/unit_tests/runnables/test_config.py b/libs/core/tests/unit_tests/runnables/test_config.py
index 9a4716e8269..4d422333cbf 100644
--- a/libs/core/tests/unit_tests/runnables/test_config.py
+++ b/libs/core/tests/unit_tests/runnables/test_config.py
@@ -95,7 +95,11 @@ def test_ensure_config_copies_model_to_metadata() -> None:
         }
     )
 
-    assert config["metadata"] == {"nooverride": 18, "model": "gpt-4o"}
+    assert config["metadata"] == {
+        "nooverride": 18,
+        "model": "gpt-4o",
+        "checkpoint_ns": "ns-1",
+    }
     assert config["configurable"] == {
         "thread_id": "th-123",
         "checkpoint_id": "ckpt-1",
@@ -157,6 +161,21 @@ def test_ensure_config_copies_top_level_model_to_metadata() -> None:
     assert config["configurable"] == {"model": "gpt-4o"}
 
 
+def test_ensure_config_copies_top_level_checkpoint_ns_to_metadata() -> None:
+    config = ensure_config(
+        cast(
+            "RunnableConfig",
+            {
+                "checkpoint_ns": "ns-1",
+                "metadata": {"nooverride": 18},
+            },
+        )
+    )
+
+    assert config["metadata"] == {"nooverride": 18, "checkpoint_ns": "ns-1"}
+    assert config["configurable"] == {"checkpoint_ns": "ns-1"}
+
+
 def test_get_langsmith_inheritable_metadata_from_config_uses_previous_copy_rules() -> (
     None
 ):