diff --git a/tests/test_tui_gateway_server.py b/tests/test_tui_gateway_server.py
index 44a66ae0f2..03d44c057a 100644
--- a/tests/test_tui_gateway_server.py
+++ b/tests/test_tui_gateway_server.py
@@ -627,7 +627,9 @@ def test_session_create_drops_pending_title_on_valueerror(monkeypatch):
     monkeypatch.setattr(_approval, "register_gateway_notify", lambda key, cb: None)
     monkeypatch.setattr(_approval, "load_permanent_allowlist", lambda: None)
 
-    resp = server.handle_request({"id": "1", "method": "session.create", "params": {"cols": 80}})
+    resp = server.handle_request(
+        {"id": "1", "method": "session.create", "params": {"cols": 80}}
+    )
     sid = resp["result"]["session_id"]
     session = server._sessions[sid]
     session["pending_title"] = "duplicate title"
@@ -670,12 +672,22 @@ def test_config_set_yolo_toggles_session_scope():
 def test_config_set_fast_updates_live_agent_and_config(monkeypatch):
     writes = []
     emits = []
-    agent = types.SimpleNamespace(service_tier=None)
+    agent = types.SimpleNamespace(
+        model="openai/gpt-5.4",
+        request_overrides={"foo": "bar", "speed": "slow"},
+        service_tier=None,
+    )
     server._sessions["sid"] = _session(agent=agent)
 
-    monkeypatch.setattr(server, "_write_config_key", lambda path, value: writes.append((path, value)))
+    monkeypatch.setattr(
+        server, "_write_config_key", lambda path, value: writes.append((path, value))
+    )
     monkeypatch.setattr(server, "_session_info", lambda _agent: {"model": "x"})
     monkeypatch.setattr(server, "_emit", lambda *args: emits.append(args))
+    monkeypatch.setattr(
+        "hermes_cli.models.resolve_fast_mode_overrides",
+        lambda _model_id: {"service_tier": "priority"},
+    )
 
     try:
         resp = server.handle_request(
@@ -687,8 +699,50 @@ def test_config_set_fast_updates_live_agent_and_config(monkeypatch):
         )
         assert resp["result"]["value"] == "fast"
         assert agent.service_tier == "priority"
+        assert agent.request_overrides == {
+            "foo": "bar",
+            "service_tier": "priority",
+        }
         assert ("agent.service_tier", "fast") in writes
         assert ("session.info", "sid", {"model": "x"}) in emits
+
+        resp_normal = server.handle_request(
+            {
+                "id": "2",
+                "method": "config.set",
+                "params": {"session_id": "sid", "key": "fast", "value": "normal"},
+            }
+        )
+        assert resp_normal["result"]["value"] == "normal"
+        assert agent.service_tier is None
+        assert agent.request_overrides == {"foo": "bar"}
+        assert ("agent.service_tier", "normal") in writes
+    finally:
+        server._sessions.pop("sid", None)
+
+
+def test_config_set_fast_status_is_non_mutating(monkeypatch):
+    writes = []
+    emits = []
+    agent = types.SimpleNamespace(service_tier="priority")
+    server._sessions["sid"] = _session(agent=agent)
+
+    monkeypatch.setattr(
+        server, "_write_config_key", lambda path, value: writes.append((path, value))
+    )
+    monkeypatch.setattr(server, "_emit", lambda *args: emits.append(args))
+
+    try:
+        resp = server.handle_request(
+            {
+                "id": "1",
+                "method": "config.set",
+                "params": {"session_id": "sid", "key": "fast", "value": "status"},
+            }
+        )
+        assert resp["result"]["value"] == "fast"
+        assert writes == []
+        assert emits == []
     finally:
         server._sessions.pop("sid", None)
 
@@ -701,7 +755,9 @@ def test_config_busy_get_and_set(monkeypatch):
         "_load_cfg",
         lambda: {"display": {"busy_input_mode": "steer"}},
     )
-    monkeypatch.setattr(server, "_write_config_key", lambda path, value: writes.append((path, value)))
+    monkeypatch.setattr(
+        server, "_write_config_key", lambda path, value: writes.append((path, value))
+    )
 
     get_resp = server.handle_request(
         {"id": "1", "method": "config.get", "params": {"key": "busy"}}
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index 68d1cfcaec..a48058674b 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -2885,10 +2885,14 @@ def _(rid, params: dict) -> dict:
         else:
             current_fast = _load_service_tier() == "priority"
 
+        if raw in {"status"}:
+            return _ok(
+                rid,
+                {"key": key, "value": "fast" if current_fast else "normal"},
+            )
+
         if raw in ("", "toggle"):
             nv = "normal" if current_fast else "fast"
-        elif raw in {"status"}:
-            nv = "fast" if current_fast else "normal"
         elif raw in {"fast", "on"}:
             nv = "fast"
         elif raw in {"normal", "off"}:
@@ -2898,8 +2902,23 @@ def _(rid, params: dict) -> dict:
 
         _write_config_key("agent.service_tier", nv)
         if session and session.get("agent") is not None:
-            session["agent"].service_tier = "priority" if nv == "fast" else None
-            _emit("session.info", params.get("session_id", ""), _session_info(session["agent"]))
+            agent = session["agent"]
+            agent.service_tier = "priority" if nv == "fast" else None
+            current_overrides = dict(getattr(agent, "request_overrides", {}) or {})
+            current_overrides.pop("service_tier", None)
+            current_overrides.pop("speed", None)
+            if nv == "fast":
+                from hermes_cli.models import resolve_fast_mode_overrides
+
+                current_overrides.update(
+                    resolve_fast_mode_overrides(getattr(agent, "model", None)) or {}
+                )
+            agent.request_overrides = current_overrides
+            _emit(
+                "session.info",
+                params.get("session_id", ""),
+                _session_info(agent),
+            )
         return _ok(rid, {"key": key, "value": nv})
 
     if key == "busy":
@@ -3188,13 +3207,12 @@ def _(rid, params: dict) -> dict:
         return _ok(
             rid,
             {
-                "value": "fast"
-                if (session := _sessions.get(params.get("session_id", "")))
-                and getattr(session.get("agent"), "service_tier", None) == "priority"
-                else (
+                "value": (
                     "fast"
-                    if _load_service_tier() == "priority"
-                    else "normal"
+                    if (session := _sessions.get(params.get("session_id", "")))
+                    and getattr(session.get("agent"), "service_tier", None)
+                    == "priority"
+                    else ("fast" if _load_service_tier() == "priority" else "normal")
                 ),
             },
         )