diff --git a/tests/gateway/test_config.py b/tests/gateway/test_config.py
index 46ceeb205c03..27992663e4f7 100644
--- a/tests/gateway/test_config.py
+++ b/tests/gateway/test_config.py
@@ -1467,3 +1467,93 @@ class TestMultiplexProfilesEnvOverride:
         for noise in ("", "   ", "maybe", "2"):
             monkeypatch.setenv("GATEWAY_MULTIPLEX_PROFILES", noise)
             assert _env_multiplex_profiles_override() is None, repr(noise)
+
+
+class TestMultiplexProfilesConfig:
+    """Tests for parsing multiplex_profiles (top-level and nested forms)."""
+
+    def test_multiplex_profiles_top_level(self, tmp_path, monkeypatch):
+        """Top-level multiplex_profiles is honored."""
+        hermes_home = tmp_path / ".hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text(
+            "multiplex_profiles: true\n",
+            encoding="utf-8",
+        )
+        monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+
+        config = load_gateway_config()
+
+        assert config.multiplex_profiles is True
+
+    def test_multiplex_profiles_nested_under_gateway(self, tmp_path, monkeypatch):
+        """gateway.multiplex_profiles (the form written by `hermes config set
+        gateway.multiplex_profiles true`) must be honored. Regression test for
+        the silent-fallback bug where the loader only forwarded the top-level
+        key, so users who wrote it under gateway: got multiplex_profiles=False
+        with no warning."""
+        hermes_home = tmp_path / ".hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text(
+            "gateway:\n  multiplex_profiles: true\n",
+            encoding="utf-8",
+        )
+        monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+
+        config = load_gateway_config()
+
+        assert config.multiplex_profiles is True, (
+            "gateway.multiplex_profiles: true was silently ignored — "
+            "loader only forwarded the top-level form"
+        )
+
+    def test_multiplex_profiles_default_false(self, tmp_path, monkeypatch):
+        """Default is False when neither form is present."""
+        hermes_home = tmp_path / ".hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text("", encoding="utf-8")
+        monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+
+        config = load_gateway_config()
+
+        assert config.multiplex_profiles is False
+
+    def test_multiplex_profiles_top_level_overrides_nested(self, tmp_path, monkeypatch):
+        """When both forms are present, top-level wins (matches profile_routes
+        and other parity bridges in load_gateway_config)."""
+        hermes_home = tmp_path / ".hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text(
+            "multiplex_profiles: true\n"
+            "gateway:\n  multiplex_profiles: false\n",
+            encoding="utf-8",
+        )
+        monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+
+        config = load_gateway_config()
+
+        assert config.multiplex_profiles is True
+
+    def test_multiplex_profiles_explicit_top_level_false_not_consulting_nested(
+        self, tmp_path, monkeypatch
+    ):
+        """Lock in the `is None` vs `is False` distinction: when top-level is
+        explicitly false, the loader must forward False WITHOUT consulting the
+        nested form (so a stale `gateway.multiplex_profiles: true` cannot
+        silently re-enable multiplexing). Guards against a future regression
+        that flips the check to `not _mp`."""
+        hermes_home = tmp_path / ".hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text(
+            "multiplex_profiles: false\n"
+            "gateway:\n  multiplex_profiles: true\n",
+            encoding="utf-8",
+        )
+        monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+
+        config = load_gateway_config()
+
+        assert config.multiplex_profiles is False, (
+            "Explicit top-level false was overridden by nested true — "
+            "loader must respect top-level precedence when key is present"
+        )