diff --git a/hermes_cli/model_switch.py b/hermes_cli/model_switch.py
index be1a095418..0e6aa4a5ec 100644
--- a/hermes_cli/model_switch.py
+++ b/hermes_cli/model_switch.py
@@ -18,7 +18,7 @@ from hermes_cli.providers import (
 from hermes_cli.model_normalize import normalize_model_for_provider
 from agent.models_dev import (
     ModelCapabilities, ModelInfo, get_model_capabilities, get_model_info, list_provider_models)
-from utils import base_url_hostname, base_url_origin
+from utils import base_url_host_matches, base_url_hostname, base_url_origin
 # Re-exported: callers/tests patch hermes_cli.model_switch.<name>.
 from hermes_cli.model_switch_providers import list_authenticated_providers
 
@@ -1309,6 +1309,17 @@ def _creds_for_current_provider(st: _Switch) -> None:
             st.resolve_runtime(requested=st.current_provider)
         except Exception:
             pass
+        # Bare ``custom``/``local`` sessions whose base_url is session-only (not a trusted config
+        # ``model.base_url``) re-resolve to the OpenRouter DEFAULT — a host the user never picked
+        # (#74143). Keep the session endpoint + key then; a config-backed custom URL still wins so
+        # key/endpoint rotation is not pinned to a stale session.
+        if (
+            st.current_provider in {"custom", "local"} and st.current_base_url
+            and (not st.base_url or base_url_host_matches(st.base_url, "openrouter.ai"))
+            and not base_url_host_matches(st.current_base_url, "openrouter.ai")
+        ):
+            st.base_url, st.api_key = st.current_base_url, st.current_api_key
+            st.api_mode = determine_api_mode(st.current_provider, st.base_url)
 
 
 def _resolve_switch_credentials(st: _Switch) -> Optional[ModelSwitchResult]:
diff --git a/tests/hermes_cli/test_model_switch_custom_providers.py b/tests/hermes_cli/test_model_switch_custom_providers.py
index a5e4768742..40b87b09a7 100644
--- a/tests/hermes_cli/test_model_switch_custom_providers.py
+++ b/tests/hermes_cli/test_model_switch_custom_providers.py
@@ -2220,3 +2220,23 @@ def test_legacy_sentinel_catalog_still_resolves_and_migrates(tmp_path, monkeypat
     assert list(saved["models"]) == _LOCAL_CATALOG
     assert "__discovered_model_catalog__" not in saved["models"]
     assert "__explicit_model_allowlist__" not in saved["models"]
+
+
+def test_same_provider_switch_on_session_only_custom_endpoint_keeps_endpoint(monkeypatch):
+    """#74143: a same-provider ``/model`` on a bare ``custom`` session whose base_url is NOT the
+    trusted config ``model.base_url`` must stay on that endpoint with its key — re-resolving from
+    config fell through to the OpenRouter default and moved the next turn to a host the user never
+    picked."""
+    for var in ("OPENROUTER_API_KEY", "OPENROUTER_BASE_URL", "CUSTOM_BASE_URL", "CUSTOM_API_KEY", "OPENAI_API_KEY"):
+        monkeypatch.delenv(var, raising=False)
+    monkeypatch.setattr("hermes_cli.model_switch.load_config", lambda: {"model": {"provider": "openrouter", "default": "x"}}, raising=False)
+    monkeypatch.setattr(
+        "hermes_cli.models.probe_api_models",
+        lambda api_key, base_url, **kw: {"models": ["m-a", "m-b"], "url": base_url + "/models", "base_url": base_url,
+                                          "suggested_base_url": None, "used_fallback": False})
+
+    result = switch_model("m-b", "custom", "m-a", "http://10.0.0.5:8000/v1", "session-secret")
+
+    assert result.success
+    assert result.base_url == "http://10.0.0.5:8000/v1"
+    assert result.api_key == "session-secret"