diff --git a/agent/moa_loop.py b/agent/moa_loop.py
index 314aaa8b0295..43691fd7f997 100644
--- a/agent/moa_loop.py
+++ b/agent/moa_loop.py
@@ -137,6 +137,36 @@ def _slot_reasoning_config(slot: dict[str, Any]) -> dict[str, Any] | None:
         return None
 
 
+def _aggregator_reasoning_config(aggregator: dict[str, Any]) -> dict[str, Any] | None:
+    """Resolve the aggregator's reasoning config: slot > per-model > global.
+
+    The aggregator is MoA's ACTING model, so when its slot doesn't pin a
+    reasoning_effort it must resolve exactly like any other acting model:
+    through the shared chokepoint (``resolve_reasoning_config``), which
+    applies ``agent.reasoning_overrides`` for the slot's model first, then
+    the global ``agent.reasoning_effort``. Without this the main loop's
+    reasoning gates (keyed to the virtual ``moa://local`` identity) never
+    fire, so the aggregator silently ran at the backend default (#64187).
+
+    Reference advisors intentionally do NOT get this fallback: they are side
+    calls (like auxiliary tasks), and inheriting a global ``xhigh`` into every
+    advisor fan-out would silently multiply cost. Their depth is slot-or-
+    provider-default only.
+    """
+    cfg = _slot_reasoning_config(aggregator)
+    if cfg is not None:
+        return cfg
+    try:
+        from hermes_cli.config import load_config
+        from hermes_constants import resolve_reasoning_config
+
+        return resolve_reasoning_config(
+            load_config() or {}, str(aggregator.get("model") or "")
+        )
+    except Exception:  # pragma: no cover - defensive; bad config must not break MoA
+        return None
+
+
 def _slot_runtime(slot: dict[str, Any]) -> dict[str, Any]:
     """Resolve a reference/aggregator slot to real runtime call kwargs.
 
@@ -694,7 +724,7 @@ def aggregate_moa_context(
             messages=agg_messages,
             temperature=aggregator_temperature,
             max_tokens=max_tokens,
-            reasoning_config=_slot_reasoning_config(aggregator),
+            reasoning_config=_aggregator_reasoning_config(aggregator),
             **agg_runtime,
         )
         synthesis = _extract_text(response)
@@ -1089,7 +1119,7 @@ class MoAChatCompletions:
             max_tokens=agg_kwargs.get("max_tokens"),
             tools=agg_kwargs.get("tools"),
             extra_body=agg_kwargs.get("extra_body"),
-            reasoning_config=_slot_reasoning_config(aggregator),
+            reasoning_config=_aggregator_reasoning_config(aggregator),
             **stream_kwargs,
             **_slot_runtime(aggregator),
         )
diff --git a/tests/agent/test_moa_reasoning_effort.py b/tests/agent/test_moa_reasoning_effort.py
index 0aa09f8b4cd3..e2ba25c4f404 100644
--- a/tests/agent/test_moa_reasoning_effort.py
+++ b/tests/agent/test_moa_reasoning_effort.py
@@ -70,3 +70,93 @@ def test_call_llm_builder_translates_reasoning_config_to_extra_body():
         reasoning_config={"enabled": False},
     )
     assert off["extra_body"]["reasoning"] == {"enabled": False}
+
+
+class TestAggregatorGlobalFallback:
+    """#64187: the aggregator (MoA's acting model) resolves like any acting
+    model when its slot has no reasoning_effort: per-model override
+    (agent.reasoning_overrides for the slot's model) > global
+    agent.reasoning_effort. Reference advisors do NOT get this fallback
+    (side calls — cost containment)."""
+
+    def test_slot_value_wins_over_global(self, monkeypatch):
+        from agent import moa_loop
+
+        monkeypatch.setattr(
+            "hermes_cli.config.load_config",
+            lambda: {"agent": {"reasoning_effort": "medium"}},
+        )
+        cfg = moa_loop._aggregator_reasoning_config({"reasoning_effort": "xhigh"})
+        assert cfg == {"enabled": True, "effort": "xhigh"}
+
+    def test_unset_slot_falls_back_to_global(self, monkeypatch):
+        from agent import moa_loop
+
+        monkeypatch.setattr(
+            "hermes_cli.config.load_config",
+            lambda: {"agent": {"reasoning_effort": "high"}},
+        )
+        cfg = moa_loop._aggregator_reasoning_config({"provider": "openrouter", "model": "m"})
+        assert cfg == {"enabled": True, "effort": "high"}
+
+    def test_unset_slot_honors_per_model_override(self, monkeypatch):
+        """The aggregator's model gets its agent.reasoning_overrides entry —
+        same resolution as any acting model, not just the bare global."""
+        from agent import moa_loop
+
+        monkeypatch.setattr(
+            "hermes_cli.config.load_config",
+            lambda: {
+                "agent": {
+                    "reasoning_effort": "medium",
+                    "reasoning_overrides": {"claude-opus-4.8": "xhigh"},
+                }
+            },
+        )
+        cfg = moa_loop._aggregator_reasoning_config(
+            {"provider": "openrouter", "model": "anthropic/claude-opus-4.8"}
+        )
+        assert cfg == {"enabled": True, "effort": "xhigh"}
+
+    def test_slot_value_beats_per_model_override(self, monkeypatch):
+        from agent import moa_loop
+
+        monkeypatch.setattr(
+            "hermes_cli.config.load_config",
+            lambda: {
+                "agent": {
+                    "reasoning_effort": "medium",
+                    "reasoning_overrides": {"claude-opus-4.8": "xhigh"},
+                }
+            },
+        )
+        cfg = moa_loop._aggregator_reasoning_config(
+            {"model": "anthropic/claude-opus-4.8", "reasoning_effort": "low"}
+        )
+        assert cfg == {"enabled": True, "effort": "low"}
+
+    def test_global_yaml_false_disables(self, monkeypatch):
+        from agent import moa_loop
+
+        monkeypatch.setattr(
+            "hermes_cli.config.load_config",
+            lambda: {"agent": {"reasoning_effort": False}},
+        )
+        cfg = moa_loop._aggregator_reasoning_config({})
+        assert cfg == {"enabled": False}
+
+    def test_no_slot_no_global_returns_none(self, monkeypatch):
+        from agent import moa_loop
+
+        monkeypatch.setattr("hermes_cli.config.load_config", lambda: {})
+        assert moa_loop._aggregator_reasoning_config({}) is None
+
+    def test_reference_slots_do_not_inherit_global(self, monkeypatch):
+        """Advisors stay slot-or-default: global effort must NOT leak in."""
+        from agent import moa_loop
+
+        monkeypatch.setattr(
+            "hermes_cli.config.load_config",
+            lambda: {"agent": {"reasoning_effort": "xhigh"}},
+        )
+        assert moa_loop._slot_reasoning_config({"provider": "p", "model": "m"}) is None