diff --git a/hermes_cli/model_switch.py b/hermes_cli/model_switch.py
index e753a8d8c7..0acecb679d 100644
--- a/hermes_cli/model_switch.py
+++ b/hermes_cli/model_switch.py
@@ -1383,7 +1383,8 @@ def _creds_for_switched_provider(st: _Switch) -> Optional[ModelSwitchResult]:
         # ANOTHER provider (the per-turn config sync adopting ``provider: custom``) the configured
         # endpoint wins, or the new model is paired with the old provider's host and key (#73680).
         # With nothing configured the resolver either raises (st.* keep the session values) or
-        # lands on OpenRouter's default (#74143) — the session endpoint is kept in both cases.
+        # lands on OpenRouter's default or the ``OPENROUTER_BASE_URL`` mirror (#74143, #10622) —
+        # the session endpoint is kept in all three cases.
         key, url = st.current_api_key, st.current_base_url
         if st.current_provider != "custom":
             with suppress(Exception):
@@ -1457,12 +1458,29 @@ def _creds_for_current_provider(st: _Switch) -> None:
 
 
 def _fell_back_to_openrouter_default(st: _Switch) -> bool:
-    """The bare-``custom`` resolver ended on OpenRouter's default host while the session was
-    elsewhere: no trusted ``model.base_url`` existed, so the URL is one the user never picked."""
+    """The bare-``custom`` resolver ended on an OpenRouter endpoint that is not a custom endpoint
+    the user configured: the built-in default host, or the ``OPENROUTER_BASE_URL`` mirror — the
+    credential ladder's last rung (#10622), which ``provider: custom`` reaches whenever no
+    trusted ``model.base_url`` / ``CUSTOM_BASE_URL`` exists."""
+    mirror = _openrouter_mirror_base_url()
+    if mirror and st.base_url.rstrip("/") == mirror:
+        return True
     return (base_url_host_matches(st.base_url, "openrouter.ai")
             and not base_url_host_matches(st.current_base_url, "openrouter.ai"))
 
 
+def _openrouter_mirror_base_url() -> str:
+    """``OPENROUTER_BASE_URL``, read the way the resolver reads it (env, or the profile's secret
+    scope). A guard read, not a credential fetch: a read that fails — unscoped under multiplexing —
+    must leave the mirror undetected so its caller keeps the session endpoint, rather than raising
+    out of ``switch_model`` where the resolver's own read of the same name is suppressed."""
+    from agent.secret_scope import get_secret_str
+    try:
+        return (get_secret_str("OPENROUTER_BASE_URL", "") or "").strip().rstrip("/")
+    except Exception:
+        return ""
+
+
 def _resolve_switch_credentials(st: _Switch) -> Optional[ModelSwitchResult]:
     """COMMON PATH part 1: credentials, direct-alias endpoint override, and the api_mode for the
     final (provider, base_url) before validation."""
diff --git a/tests/hermes_cli/test_model_switch_custom_providers.py b/tests/hermes_cli/test_model_switch_custom_providers.py
index 1e62aa45d9..a733df602b 100644
--- a/tests/hermes_cli/test_model_switch_custom_providers.py
+++ b/tests/hermes_cli/test_model_switch_custom_providers.py
@@ -561,6 +561,52 @@ def test_switch_to_bare_custom_with_no_configured_endpoint_keeps_the_current_one
     assert (result.base_url, result.api_key) == ("https://api.anthropic.com", "sk-ant")
 
 
+def test_openrouter_mirror_read_never_raises_without_a_secret_scope(monkeypatch):
+    """The mirror guard reads ``OPENROUTER_BASE_URL`` through the profile secret scope: with
+    multiplexing on and no scope installed that read raises ``UnscopedSecretError``. A guard read
+    must degrade to 'no mirror detected' (the caller then keeps the session endpoint) instead of
+    propagating out of ``switch_model``, where the resolver's own read of the same name is
+    suppressed."""
+    from agent import secret_scope
+    from hermes_cli.model_switch import _openrouter_mirror_base_url
+
+    monkeypatch.setenv("OPENROUTER_BASE_URL", "https://mirror.example.com/v1")
+    secret_scope.set_multiplex_active(True)
+    try:
+        assert _openrouter_mirror_base_url() == ""
+    finally:
+        secret_scope.set_multiplex_active(False)
+
+
+def test_switch_to_bare_custom_ignores_an_openrouter_mirror(monkeypatch, tmp_path):
+    """#115661 follow-up: with ``OPENROUTER_BASE_URL`` set to a mirror and nothing configured for
+    ``custom``, the ladder's last rung hands back that mirror — a host the user configured for
+    OpenRouter — with the ``no-key-required`` placeholder. It must not replace the session's own
+    endpoint and key (the switched arm used to adopt it, dropping a working credential)."""
+    home = tmp_path / "hermes-home"
+    home.mkdir()
+    (home / "config.yaml").write_text("model:\n  default: m\n  provider: custom\n", encoding="utf-8")
+    monkeypatch.setenv("HERMES_HOME", str(home))
+    monkeypatch.setenv("OPENROUTER_BASE_URL", "https://mirror.example.com/v1")
+    monkeypatch.setattr("hermes_cli.models_validate.validate_requested_model", lambda *a, **k: _MOCK_VALIDATION)
+    monkeypatch.setattr("hermes_cli.model_switch.get_model_info", lambda *a, **k: None)
+    monkeypatch.setattr("hermes_cli.model_switch.get_model_capabilities", lambda *a, **k: None)
+
+    result = switch_model(
+        raw_input="m2",
+        current_provider="anthropic",
+        current_model="m",
+        current_base_url="https://api.anthropic.com",
+        current_api_key="sk-ant",
+        explicit_provider="custom",
+        user_providers={},
+        custom_providers=[],
+    )
+
+    assert result.success is True
+    assert (result.base_url, result.api_key) == ("https://api.anthropic.com", "sk-ant")
+
+
 def test_is_aggregator_recognizes_named_custom_provider():
     assert providers_mod.is_aggregator("custom:hpc-ai") is True
     assert providers_mod.is_aggregator("custom:litellm") is True