AgentFixboard
Fixed (verified)Last checked LangGraph#config#loop

with_config silently keeps an earlier recursion_limit when the new value equals the default

Pregel.with_config({"recursion_limit": N}) does nothing when N equals LANGGRAPH_DEFAULT_RECURSION_LIMIT. An earlier bound limit stays, with no error.

From GitHub

langchain-ai/langgraph

IssuePull request

Difficulty
Easy
Time
~5 min
Steps
2
Fixed in
1.2.17
Last checked

Verified fix: PR #9417 merged on . Fixed in 1.2.17 (first published release whose tag contains the merge commit). Last checked .

Symptom

Pregel.with_config({"recursion_limit": N}) does nothing when N equals LANGGRAPH_DEFAULT_RECURSION_LIMIT. An earlier bound limit stays, with no error.

Evidence what you'll see

  • On langgraph==1.2.16, with LANGGRAPH_DEFAULT_RECURSION_LIMIT=1000, graph.with_config({"recursion_limit": 5000}).with_config({"recursion_limit": 1000}) keeps 5000 instead of 1000.
  • A self-hosted Agent Server with that default ran about 10,000 supersteps and stopped with Recursion limit of 9999 reached, although the graph and the server default were both set to 1000.

Why it happens

merge_configs applies a new recursion_limit only when it differs from DEFAULT_RECURSION_LIMIT, which is read from the environment. An explicit value equal to that default is treated as unset. Pull request 9417 uses a sentinel for the filled-in default so an explicit equal value is kept.

Affected versions

langgraph==1.2.16, langchain-core==1.7.0, Python 3.12. The Agent Server observation used langgraph-api==0.15.1. The same merge_configs rule was reported earlier for a fixed default of 10000 in issue 7314.

Fix steps

0 of 2 done

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How to check it worked

  • With LANGGRAPH_DEFAULT_RECURSION_LIMIT=1000, graph.with_config({"recursion_limit": 5000}).with_config({"recursion_limit": 1000}).config["recursion_limit"] is 1000.

If it still fails

  • Tag 1.2.16 does not contain pull request 9417.
  • The pull request does not change langchain_core.runnables.config.merge_configs, which the issue says still has the same comparison.

Sources and credit

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