RunnableWithFallbacks.invoke() drops parent_run_id for child callback events (regression from #25550) #36072
Description
Checked other resources
- This is a bug, not a usage question.
- I added a clear and descriptive title that summarizes this issue.
- I used the GitHub search to find a similar question and didn't find it.
- I am sure that this is a bug in LangChain rather than my code.
- The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).
- This is not related to the langchain-community package.
- I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS.
Package (Required)
- langchain
- langchain-openai
- langchain-anthropic
- langchain-classic
- langchain-core
- langchain-model-profiles
- langchain-tests
- langchain-text-splitters
- langchain-chroma
- langchain-deepseek
- langchain-exa
- langchain-fireworks
- langchain-groq
- langchain-huggingface
- langchain-mistralai
- langchain-nomic
- langchain-ollama
- langchain-openrouter
- langchain-perplexity
- langchain-qdrant
- langchain-xai
- Other / not sure / general
Related Issues / PRs
#25337 — Original bug report (callbacks not firing in fallbacks), closed by #25550
#25550 — PR that introduced this regression (passed config instead of child_config)
Reproduction Steps / Example Code (Python)
from langchain_openai import ChatOpenAI
from langchain_core.callbacks.base import BaseCallbackHandler
from langchain_core.messages import HumanMessage
class Tracker(BaseCallbackHandler):
def __init__(self):
self.events = []
def on_chain_start(self, serialized, inputs, *, run_id, parent_run_id=None, **kwargs):
self.events.append(("chain_start", run_id, parent_run_id))
def on_chat_model_start(self, serialized, messages, *, run_id, parent_run_id=None, **kwargs):
self.events.append(("chat_model_start", run_id, parent_run_id))
def on_llm_error(self, error, *, run_id, parent_run_id=None, **kwargs):
self.events.append(("llm_error", run_id, parent_run_id))
tracker = Tracker()
llm = ChatOpenAI(model="gpt-4o-mini", api_key="sk-bad").with_fallbacks(
[ChatOpenAI(model="gpt-4o-mini", api_key="sk-bad-2")]
)
try:
llm.invoke([HumanMessage(content="hi")], config={"callbacks": [tracker]})
except Exception:
pass
chain_run_id = tracker.events[0][1] # run_id from chain_start
for event_name, run_id, parent_run_id in tracker.events:
if event_name in ("chat_model_start", "llm_error"):
assert parent_run_id == chain_run_id, (
f"{event_name}: expected parent_run_id={chain_run_id}, got {parent_run_id}"
)Error Message and Stack Trace (if applicable)
Description
RunnableWithFallbacks.invoke() passes config instead of child_config to child runnables (line 196 of
fallbacks.py). This causes child callback events (on_chat_model_start, on_llm_error, on_llm_end) to
receive parent_run_id=None instead of the fallback chain's run_id.
This breaks any tracing/observability tool that relies on parent_run_id to build span trees — child LLM
spans become orphans invisible to the trace.
Regression introduced by #25550. Fix is one line — change config to child_config:
child_config = patch_config(config, callbacks=run_manager.get_child())
with set_config_context(child_config) as context:
output = context.run(
runnable.invoke,
input,
- config,
+ child_config,
**kwargs,
)
Same issue likely applies to ainvoke, batch, and abatch.
System Info
from langchain_core import sys_info
sys_info.print_sys_info()
System Information
OS: Darwin
OS Version: Darwin Kernel Version 25.3.0: Wed Jan 28 20:56:35 PST 2026; root:xnu-12377.91.3~2/RELEASE_ARM64_T6030
Python Version: 3.12.8 (main, Dec 6 2024, 19:42:06) [Clang 18.1.8 ]
Package Information
langchain_core: 1.2.19
langchain: 1.2.10
langsmith: 0.7.9
langchain_google_vertexai: 3.2.2
langchain_openai: 1.1.10
langchain_tests: 1.1.5
langgraph_sdk: 0.3.9
Optional packages not installed
deepagents
deepagents-cli
Other Dependencies
bottleneck: 1.6.0
google-cloud-aiplatform: 1.139.0
google-cloud-storage: 3.9.0
google-cloud-vectorsearch: 0.5.0
httpx: 0.28.1
httpx-sse: 0.4.3
jsonpatch: 1.33
langgraph: 1.0.10
numexpr: 2.14.1
numpy: 2.4.2
openai: 2.29.0
openai-agents: 0.12.4
opentelemetry-api: 1.39.1
opentelemetry-exporter-otlp-proto-http: 1.39.1
opentelemetry-sdk: 1.39.1
orjson: 3.11.7
packaging: 26.0
pyarrow: 22.0.0
pydantic: 2.12.5
pytest: 9.0.2
pytest-asyncio: 1.3.0
pytest-benchmark: 5.2.3
pytest-codspeed: 4.3.0
pytest-recording: 0.13.4
pytest-socket: 0.7.0
pyyaml: 6.0.3
requests: 2.32.5
requests-toolbelt: 1.0.0
rich: 14.3.3
syrupy: 5.1.0
tenacity: 9.1.4
tiktoken: 0.12.0
typing-extensions: 4.15.0
uuid-utils: 0.14.1
validators: 0.35.0
vcrpy: 8.1.1
websockets: 16.0
wrapt: 1.17.3
xxhash: 3.6.0
zstandard: 0.25.0