diff --git a/src/hyperloom/inference_optimizer/tests/test_grid_variant_filter.py b/src/hyperloom/inference_optimizer/tests/test_grid_variant_filter.py
new file mode 100644
index 000000000..99f88b310
--- /dev/null
+++ b/src/hyperloom/inference_optimizer/tests/test_grid_variant_filter.py
@@ -0,0 +1,131 @@
+# SPDX-FileCopyrightText: 2026 Advanced Micro Devices, Inc.
+# SPDX-License-Identifier: MIT
+
+"""Unit tests for apply_multi_node_invalid_variants."""
+
+from __future__ import annotations
+
+import pytest
+
+from hyperloom.orchestrator.actions.executors import _multi_node_env as mn
+from hyperloom.orchestrator.actions.executors._grid_base import GridVariant
+from hyperloom.orchestrator.actions.executors._grid_variant_filter import (
+    apply_multi_node_invalid_variants,
+)
+
+
+def _v(name: str, *, args: str = "") -> GridVariant:
+    return GridVariant(name=name, extra_server_args=args)
+
+
+@pytest.fixture()
+def _multi_node(monkeypatch):
+    monkeypatch.setattr(mn, "is_multi_node", lambda: True)
+
+
+def test_single_node_is_a_strict_noop(monkeypatch):
+    monkeypatch.setattr(mn, "is_multi_node", lambda: False)
+    monkeypatch.setenv("CONC", "64")
+    grid = [
+        _v("low-graph", args="--cuda-graph-max-bs 8"),
+        _v("keep", args="--cuda-graph-max-bs 64"),
+    ]
+    kept, dropped = apply_multi_node_invalid_variants(grid)
+    # Identity is the production contract: single-node returns the input
+    # list (`return grid, []`), not a copy. Sibling filters copy on their
+    # no-op path; this one does not, so `is` is the pin.
+    assert kept is grid
+    assert dropped == []
+
+
+def test_multi_node_drops_cuda_graph_max_bs_below_conc(_multi_node, monkeypatch):
+    monkeypatch.setenv("CONC", "64")
+    grid = [
+        _v("space-form", args="--cuda-graph-max-bs 32"),
+        _v("equals-form", args="--cuda_graph_max_bs=8"),
+        _v("at-threshold", args="--cuda-graph-max-bs 64"),
+        _v("above", args="--cuda-graph-max-bs 128"),
+        _v("no-flag", args="--chunked-prefill-size 8192"),
+    ]
+    kept, dropped = apply_multi_node_invalid_variants(grid)
+    assert [v.name for v in kept] == ["at-threshold", "above", "no-flag"]
+    assert [row["name"] for row in dropped] == ["space-form", "equals-form"]
+    assert all(row["source"] == "multi_node_invalid" for row in dropped)
+    assert "CONC=64" in dropped[0]["reason"]
+    assert "cuda_graph_max_bs=32" in dropped[0]["reason"]
+
+
+def test_conc_zero_does_not_drop(_multi_node, monkeypatch):
+    # Documents observable behaviour: CONC=0 never drops anything.
+    # The `conc > 0 and` guard was removed from production because the regex
+    # (\d+) guarantees conc is always >= 0, making the guard unreachable; the
+    # invariant is preserved by `n < conc` being False for all n >= 1 when conc=0.
+    monkeypatch.setenv("CONC", "0")
+    grid = [_v("low-graph", args="--cuda-graph-max-bs 1")]
+    kept, dropped = apply_multi_node_invalid_variants(grid)
+    assert [v.name for v in kept] == ["low-graph"]
+    assert dropped == []
+
+
+def test_multi_node_flag_in_non_leading_position_is_detected(_multi_node, monkeypatch):
+    """The filter uses re.search(), not re.match() — flag anywhere in the string must fire."""
+    monkeypatch.setenv("CONC", "64")
+    grid = [
+        _v("multi-flag-drop", args="--tp 8 --cuda-graph-max-bs 32"),
+        _v("multi-flag-keep", args="--tp 8 --cuda-graph-max-bs 128"),
+    ]
+    kept, dropped = apply_multi_node_invalid_variants(grid)
+    assert [v.name for v in kept] == ["multi-flag-keep"]
+    assert [row["name"] for row in dropped] == ["multi-flag-drop"]
+    assert "cuda_graph_max_bs=32" in dropped[0]["reason"]
+    assert "CONC=64" in dropped[0]["reason"]
+
+
+def test_conc_unset_defaults_to_64(_multi_node, monkeypatch):
+    """CONC env var absent → the os.environ.get default of '64' applies."""
+    monkeypatch.delenv("CONC", raising=False)
+    grid = [
+        _v("below-default", args="--cuda-graph-max-bs 32"),
+        _v("at-default", args="--cuda-graph-max-bs 64"),
+    ]
+    kept, dropped = apply_multi_node_invalid_variants(grid)
+    assert [v.name for v in kept] == ["at-default"]
+    assert [row["name"] for row in dropped] == ["below-default"]
+    assert "CONC=64" in dropped[0]["reason"]
+    assert "cuda_graph_max_bs=32" in dropped[0]["reason"]
+
+
+def test_conc_empty_string_defaults_to_64(_multi_node, monkeypatch):
+    """CONC='' → the `or 64` branch applies (empty string is falsy)."""
+    monkeypatch.setenv("CONC", "")
+    grid = [
+        _v("below-default", args="--cuda-graph-max-bs 32"),
+        _v("at-default", args="--cuda-graph-max-bs 64"),
+    ]
+    kept, dropped = apply_multi_node_invalid_variants(grid)
+    assert [v.name for v in kept] == ["at-default"]
+    assert [row["name"] for row in dropped] == ["below-default"]
+    assert "CONC=64" in dropped[0]["reason"]
+    assert "cuda_graph_max_bs=32" in dropped[0]["reason"]
+
+
+def test_unparseable_conc_falls_back_to_64(_multi_node, monkeypatch):
+    monkeypatch.setenv("CONC", "not-an-int")
+    grid = [
+        _v("below-default", args="--cuda-graph-max-bs 32"),
+        _v("at-default", args="--cuda-graph-max-bs 64"),
+    ]
+    kept, dropped = apply_multi_node_invalid_variants(grid)
+    assert [v.name for v in kept] == ["at-default"]
+    assert [row["name"] for row in dropped] == ["below-default"]
+    assert "CONC=64" in dropped[0]["reason"]
+    assert "cuda_graph_max_bs=32" in dropped[0]["reason"]
+
+
+def test_none_extra_server_args_is_treated_as_empty(_multi_node, monkeypatch):
+    """`v.extra_server_args or ""` must not raise or match when args is None."""
+    monkeypatch.setenv("CONC", "64")
+    v = GridVariant(name="none-args", extra_server_args=None)
+    kept, dropped = apply_multi_node_invalid_variants([v])
+    assert kept == [v]
+    assert dropped == []
diff --git a/src/hyperloom/orchestrator/actions/executors/_grid_variant_filter.py b/src/hyperloom/orchestrator/actions/executors/_grid_variant_filter.py
index 50c3d071a..b9aca80f5 100644
--- a/src/hyperloom/orchestrator/actions/executors/_grid_variant_filter.py
+++ b/src/hyperloom/orchestrator/actions/executors/_grid_variant_filter.py
@@ -199,7 +199,7 @@ def apply_multi_node_invalid_variants(
     dropped: list[dict] = []
     for v in grid:
         m = _RE_CUDA_GRAPH_MAX_BS.search(v.extra_server_args or "")
-        if conc > 0 and m and int(m.group(1)) < conc:
+        if m and int(m.group(1)) < conc:
             dropped.append(
                 {
                     "name": v.name,