diff --git a/.github/scripts/close_low_quality_prs.py b/.github/scripts/close_low_quality_prs.py
index 95335aec167..43141a38a61 100644
--- a/.github/scripts/close_low_quality_prs.py
+++ b/.github/scripts/close_low_quality_prs.py
@@ -35,7 +35,7 @@ import json
 import re
 import subprocess
 import sys
-from typing import Any, Iterable
+from typing import Iterable
 
 # Greptile's GitHub App appears as `greptile-apps[bot]` in REST API comments
 # and `greptile-apps` in `gh pr view --json` output. Accept either form.
@@ -54,6 +54,12 @@ SCORE_PATTERN = re.compile(
 # exempt from auto-triage.
 INTERNAL_AUTHOR_ASSOCIATIONS = frozenset({"OWNER", "MEMBER", "COLLABORATOR"})
 
+# Default labels that exempt a PR from auto-close. Defined at module scope (not
+# as a mutable argparse default) so that `--optout-label foo` REPLACES the
+# defaults instead of appending to them — the argparse `action="append"` +
+# `default=[...]` combination silently mutates the shared default list.
+DEFAULT_OPTOUT_LABELS = ("do not close", "keep open", "wip")
+
 
 def gh(*args: str) -> str:
     """Run a `gh` CLI command and return stdout. Raises on non-zero exit."""
@@ -66,11 +72,6 @@ def gh(*args: str) -> str:
     return result.stdout
 
 
-def gh_json(*args: str) -> Any:
-    """Run a `gh` CLI command that emits JSON and return the parsed value."""
-    return json.loads(gh(*args))
-
-
 def fetch_open_prs(repo: str | None) -> list[dict]:
     """Fetch all open PRs (number, createdAt, isDraft, labels, author)."""
     repo_args = ["--repo", repo] if repo else []
@@ -297,10 +298,13 @@ def main() -> int:
     parser.add_argument(
         "--optout-label",
         action="append",
-        default=["do not close", "keep open", "wip"],
+        default=None,
         help=(
-            "Label(s) that exempt a PR from auto-close. "
-            "Repeat to add more. Case-insensitive."
+            "Label(s) that exempt a PR from auto-close. Repeat to add more. "
+            "Case-insensitive. When omitted, defaults to "
+            f"{list(DEFAULT_OPTOUT_LABELS)!r}; passing this flag REPLACES the "
+            "defaults (argparse `append` with a mutable default would append "
+            "instead, which we explicitly avoid)."
         ),
     )
     parser.add_argument(
@@ -334,7 +338,7 @@ def main() -> int:
     print(f"Found {len(prs)} open PRs.\n")
 
     now = dt.datetime.now(dt.timezone.utc)
-    optout_labels = set(args.optout_label)
+    optout_labels = set(args.optout_label or DEFAULT_OPTOUT_LABELS)
 
     closed = 0
     summary = {
diff --git a/tests/test_litellm/test_github_close_low_quality_prs.py b/tests/test_litellm/test_github_close_low_quality_prs.py
index 0d63562ec0f..6d1ad50012e 100644
--- a/tests/test_litellm/test_github_close_low_quality_prs.py
+++ b/tests/test_litellm/test_github_close_low_quality_prs.py
@@ -292,6 +292,84 @@ class TestEvaluatePr:
         assert score is None
 
 
+class TestMainOptoutLabelDefault:
+    """`--optout-label` must REPLACE the canonical defaults, not append."""
+
+    def _patch_no_op(self, closer_module, monkeypatch):
+        monkeypatch.setattr(closer_module, "fetch_open_prs", lambda repo: [])
+        # `optout_labels` is captured indirectly via evaluate_pr; sniff the
+        # set passed in by stubbing evaluate_pr.
+        captured: dict = {}
+
+        def fake_evaluate(pr, now, min_age_days, min_score, repo, optout_labels):
+            captured["optout_labels"] = set(optout_labels)
+            return ("skip-draft", None, None)
+
+        monkeypatch.setattr(closer_module, "evaluate_pr", fake_evaluate)
+        return captured
+
+    def test_should_use_canonical_defaults_when_flag_omitted(
+        self, closer_module, monkeypatch
+    ):
+        captured = self._patch_no_op(closer_module, monkeypatch)
+        # No PRs -> capture won't fire; instead inject one synthetic PR via
+        # fetch_open_prs so evaluate_pr is invoked at least once.
+        monkeypatch.setattr(
+            closer_module,
+            "fetch_open_prs",
+            lambda repo: [
+                {
+                    "number": 1,
+                    "title": "p",
+                    "createdAt": "2026-05-10T00:00:00Z",
+                    "isDraft": True,
+                    "labels": [],
+                    "author": {"login": "x"},
+                }
+            ],
+        )
+        monkeypatch.setattr(sys, "argv", ["close_low_quality_prs.py"])
+        rc = closer_module.main()
+        assert rc == 0
+        assert captured["optout_labels"] == set(closer_module.DEFAULT_OPTOUT_LABELS)
+
+    def test_should_replace_defaults_when_flag_provided(
+        self, closer_module, monkeypatch
+    ):
+        captured = self._patch_no_op(closer_module, monkeypatch)
+        monkeypatch.setattr(
+            closer_module,
+            "fetch_open_prs",
+            lambda repo: [
+                {
+                    "number": 1,
+                    "title": "p",
+                    "createdAt": "2026-05-10T00:00:00Z",
+                    "isDraft": True,
+                    "labels": [],
+                    "author": {"login": "x"},
+                }
+            ],
+        )
+        monkeypatch.setattr(
+            sys,
+            "argv",
+            [
+                "close_low_quality_prs.py",
+                "--optout-label",
+                "hold",
+                "--optout-label",
+                "needs-discussion",
+            ],
+        )
+        rc = closer_module.main()
+        assert rc == 0
+        # Crucially, none of the canonical defaults leak in.
+        assert captured["optout_labels"] == {"hold", "needs-discussion"}
+        for default in closer_module.DEFAULT_OPTOUT_LABELS:
+            assert default not in captured["optout_labels"], default
+
+
 class TestHasOptoutLabel:
     def test_should_match_label_case_insensitively(self, closer_module):
         pr = {"labels": [{"name": "Do Not Close"}, {"name": "bug"}]}