diff --git a/gateway/run.py b/gateway/run.py
index 03c1e3d8f8..4c82a9274b 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -638,6 +638,7 @@ class GatewayRunner:
     _restart_via_service: bool = False
     _stop_task: Optional[asyncio.Task] = None
     _session_model_overrides: Dict[str, Dict[str, str]] = {}
+    _session_reasoning_overrides: Dict[str, Dict[str, Any]] = {}
     
     def __init__(self, config: Optional[GatewayConfig] = None):
         self.config = config or load_gateway_config()
@@ -701,6 +702,9 @@ class GatewayRunner:
         # Per-session model overrides from /model command.
         # Key: session_key, Value: dict with model/provider/api_key/base_url/api_mode
         self._session_model_overrides: Dict[str, Dict[str, str]] = {}
+        # Per-session reasoning effort overrides from /reasoning.
+        # Key: session_key, Value: parsed reasoning config dict.
+        self._session_reasoning_overrides: Dict[str, Dict[str, Any]] = {}
         # Track pending exec approvals per session
         # Key: session_key, Value: {"command": str, "pattern_key": str, ...}
         self._pending_approvals: Dict[str, Dict[str, Any]] = {}
@@ -1263,6 +1267,66 @@ class GatewayRunner:
             logger.warning("Unknown reasoning_effort '%s', using default (medium)", effort)
         return result
 
+    @staticmethod
+    def _parse_reasoning_command_args(raw_args: str) -> tuple[str, bool]:
+        """Parse `/reasoning` args into `(value, persist_global)`.
+
+        `/reasoning <level>` is session-scoped by default. `--global` may be
+        supplied in any position to persist the change to config.yaml.
+        """
+        import shlex
+
+        text = str(raw_args or "").strip().replace("—", "--")
+        if not text:
+            return "", False
+        try:
+            tokens = shlex.split(text)
+        except ValueError:
+            tokens = text.split()
+
+        persist_global = False
+        value_tokens = []
+        for token in tokens:
+            if token == "--global":
+                persist_global = True
+            else:
+                value_tokens.append(token)
+        return " ".join(value_tokens).strip().lower(), persist_global
+
+    def _resolve_session_reasoning_config(
+        self,
+        *,
+        source: Optional[SessionSource] = None,
+        session_key: Optional[str] = None,
+    ) -> dict | None:
+        """Resolve reasoning effort for a session, honoring session overrides."""
+        resolved_session_key = session_key
+        if not resolved_session_key and source is not None:
+            try:
+                resolved_session_key = self._session_key_for_source(source)
+            except Exception:
+                resolved_session_key = None
+
+        overrides = getattr(self, "_session_reasoning_overrides", {}) or {}
+        if resolved_session_key and resolved_session_key in overrides:
+            return overrides[resolved_session_key]
+        return self._load_reasoning_config()
+
+    def _set_session_reasoning_override(
+        self,
+        session_key: str,
+        reasoning_config: Optional[dict],
+    ) -> None:
+        """Set or clear the session-scoped reasoning override."""
+        if not session_key:
+            return
+        if not hasattr(self, "_session_reasoning_overrides"):
+            self._session_reasoning_overrides = {}
+        if reasoning_config is None:
+            self._session_reasoning_overrides.pop(session_key, None)
+        else:
+            self._session_reasoning_overrides[session_key] = dict(reasoning_config)
+
     @staticmethod
     def _load_service_tier() -> str | None:
         """Load Priority Processing setting from config.yaml.
@@ -3982,6 +4046,8 @@ class GatewayRunner:
         # Get or create session
         session_entry = self.session_store.get_or_create_session(source)
         session_key = session_entry.session_key
+        if getattr(session_entry, "was_auto_reset", False):
+            self._set_session_reasoning_override(session_key, None)
         
         # Emit session:start for new or auto-reset sessions
         _is_new_session = (
@@ -4652,6 +4718,7 @@ class GatewayRunner:
                 self.session_store.reset_session(session_key)
                 self._evict_cached_agent(session_key)
                 self._session_model_overrides.pop(session_key, None)
+                self._set_session_reasoning_override(session_key, None)
                 response = (response or "") + (
                     "\n\n🔄 Session auto-reset — the conversation exceeded the "
                     "maximum context size and could not be compressed further. "
@@ -4928,9 +4995,10 @@ class GatewayRunner:
         # Reset the session
         new_entry = self.session_store.reset_session(session_key)
 
-        # Clear any session-scoped model override so the next agent picks up
-        # the configured default instead of the previously switched model.
+        # Clear any session-scoped model/reasoning overrides so the next agent
+        # picks up configured defaults instead of previous session switches.
         self._session_model_overrides.pop(session_key, None)
+        self._set_session_reasoning_override(session_key, None)
 
         # Clear session-scoped dangerous-command approvals and /yolo state.
         # /new is a conversation-boundary operation — approval state from the
@@ -6417,7 +6485,7 @@ class GatewayRunner:
 
             pr = self._provider_routing
             max_iterations = int(os.getenv("HERMES_MAX_ITERATIONS", "90"))
-            reasoning_config = self._load_reasoning_config()
+            reasoning_config = self._resolve_session_reasoning_config(source=source)
             self._reasoning_config = reasoning_config
             self._service_tier = self._load_service_tier()
             turn_route = self._resolve_turn_agent_config(prompt, model, runtime_kwargs)
@@ -6590,7 +6658,10 @@ class GatewayRunner:
                 return
 
             platform_key = _platform_config_key(source.platform)
-            reasoning_config = self._load_reasoning_config()
+            reasoning_config = self._resolve_session_reasoning_config(
+                source=source,
+                session_key=session_key,
+            )
             self._service_tier = self._load_service_tier()
             turn_route = self._resolve_turn_agent_config(question, model, runtime_kwargs)
             pr = self._provider_routing
@@ -6696,17 +6767,24 @@ class GatewayRunner:
         """Handle /reasoning command — manage reasoning effort and display toggle.
 
         Usage:
-            /reasoning              Show current effort level and display state
-            /reasoning <level>      Set reasoning effort (none, minimal, low, medium, high, xhigh)
-            /reasoning show|on      Show model reasoning in responses
-            /reasoning hide|off     Hide model reasoning from responses
+            /reasoning                       Show current effort level and display state
+            /reasoning <level>               Set reasoning effort for this session only
+            /reasoning <level> --global      Persist reasoning effort to config.yaml
+            /reasoning reset                 Clear this session's reasoning override
+            /reasoning show|on               Show model reasoning in responses
+            /reasoning hide|off              Hide model reasoning from responses
         """
         import yaml
 
-        args = event.get_command_args().strip().lower()
+        raw_args = event.get_command_args().strip()
+        args, persist_global = self._parse_reasoning_command_args(raw_args)
         config_path = _hermes_home / "config.yaml"
-        self._reasoning_config = self._load_reasoning_config()
+        session_key = self._session_key_for_source(event.source)
         self._show_reasoning = self._load_show_reasoning()
+        self._reasoning_config = self._resolve_session_reasoning_config(
+            source=event.source,
+            session_key=session_key,
+        )
 
         def _save_config_key(key_path: str, value):
             """Save a dot-separated key to config.yaml."""
@@ -6728,7 +6806,7 @@ class GatewayRunner:
                 logger.error("Failed to save config key %s: %s", key_path, e)
                 return False
 
-        if not args:
+        if not raw_args:
             # Show current state
             rc = self._reasoning_config
             if rc is None:
@@ -6738,11 +6816,14 @@ class GatewayRunner:
             else:
                 level = rc.get("effort", "medium")
             display_state = "on ✓" if self._show_reasoning else "off"
+            has_session_override = session_key in (getattr(self, "_session_reasoning_overrides", {}) or {})
+            scope = "session override" if has_session_override else "global config"
             return (
                 "🧠 **Reasoning Settings**\n\n"
                 f"**Effort:** `{level}`\n"
+                f"**Scope:** {scope}\n"
                 f"**Display:** {display_state}\n\n"
-                "_Usage:_ `/reasoning <none|minimal|low|medium|high|xhigh|show|hide>`"
+                "_Usage:_ `/reasoning <none|minimal|low|medium|high|xhigh|reset|show|hide> [--global]`"
             )
 
         # Display toggle (per-platform)
@@ -6762,22 +6843,38 @@ class GatewayRunner:
 
         # Effort level change
         effort = args.strip()
+        if effort == "reset":
+            if persist_global:
+                return "⚠️ `/reasoning reset --global` is not supported. Use `/reasoning <level> --global` to change the global default."
+            self._set_session_reasoning_override(session_key, None)
+            self._reasoning_config = self._load_reasoning_config()
+            self._evict_cached_agent(session_key)
+            return "🧠 ✓ Session reasoning override cleared; falling back to global config."
         if effort == "none":
             parsed = {"enabled": False}
         elif effort in ("minimal", "low", "medium", "high", "xhigh"):
             parsed = {"enabled": True, "effort": effort}
         else:
             return (
-                f"⚠️ Unknown argument: `{effort}`\n\n"
+                f"⚠️ Unknown argument: `{effort or raw_args.lower()}`\n\n"
                 "**Valid levels:** none, minimal, low, medium, high, xhigh\n"
-                "**Display:** show, hide"
+                "**Display:** show, hide\n"
+                "**Persist:** add `--global` to save beyond this session"
             )
 
         self._reasoning_config = parsed
-        if _save_config_key("agent.reasoning_effort", effort):
-            return f"🧠 ✓ Reasoning effort set to `{effort}` (saved to config)\n_(takes effect on next message)_"
-        else:
-            return f"🧠 ✓ Reasoning effort set to `{effort}` (this session only)"
+        if persist_global:
+            if _save_config_key("agent.reasoning_effort", effort):
+                self._set_session_reasoning_override(session_key, None)
+                self._evict_cached_agent(session_key)
+                return f"🧠 ✓ Reasoning effort set to `{effort}` (saved to config)\n_(takes effect on next message)_"
+            self._set_session_reasoning_override(session_key, parsed)
+            self._evict_cached_agent(session_key)
+            return f"🧠 ✓ Reasoning effort set to `{effort}` (session only — config save failed)\n_(takes effect on next message)_"
+
+        self._set_session_reasoning_override(session_key, parsed)
+        self._evict_cached_agent(session_key)
+        return f"🧠 ✓ Reasoning effort set to `{effort}` (session only — add `--global` to persist)\n_(takes effect on next message)_"
 
     async def _handle_fast_command(self, event: MessageEvent) -> str:
         """Handle /fast — mirror the CLI Priority Processing toggle in gateway chats."""
@@ -9579,7 +9676,10 @@ class GatewayRunner:
                 }
 
             pr = self._provider_routing
-            reasoning_config = self._load_reasoning_config()
+            reasoning_config = self._resolve_session_reasoning_config(
+                source=source,
+                session_key=session_key,
+            )
             self._reasoning_config = reasoning_config
             self._service_tier = self._load_service_tier()
             # Set up stream consumer for token streaming or interim commentary.
diff --git a/tests/gateway/test_reasoning_command.py b/tests/gateway/test_reasoning_command.py
index e39ed1123d..5020df30a7 100644
--- a/tests/gateway/test_reasoning_command.py
+++ b/tests/gateway/test_reasoning_command.py
@@ -33,6 +33,7 @@ def _make_runner():
     runner._ephemeral_system_prompt = ""
     runner._prefill_messages = []
     runner._reasoning_config = None
+    runner._session_reasoning_overrides = {}
     runner._show_reasoning = False
     runner._provider_routing = {}
     runner._fallback_model = None
@@ -76,6 +77,10 @@ class TestReasoningCommand:
         source = inspect.getsource(gateway_run.GatewayRunner._handle_message)
         assert '"reasoning"' in source
 
+    def test_parse_reasoning_command_args_accepts_ascii_and_smart_global_flags(self):
+        assert gateway_run.GatewayRunner._parse_reasoning_command_args("high --global") == ("high", True)
+        assert gateway_run.GatewayRunner._parse_reasoning_command_args("—global xhigh") == ("xhigh", True)
+
     @pytest.mark.asyncio
     async def test_reasoning_command_reloads_current_state_from_config(self, tmp_path, monkeypatch):
         hermes_home = tmp_path / "hermes"
@@ -111,13 +116,90 @@ class TestReasoningCommand:
         runner = _make_runner()
         runner._reasoning_config = {"enabled": True, "effort": "medium"}
 
-        result = await runner._handle_reasoning_command(_make_event("/reasoning low"))
+        result = await runner._handle_reasoning_command(_make_event("/reasoning low --global"))
 
         saved = yaml.safe_load(config_path.read_text(encoding="utf-8"))
         assert saved["agent"]["reasoning_effort"] == "low"
         assert runner._reasoning_config == {"enabled": True, "effort": "low"}
         assert "takes effect on next message" in result
 
+    @pytest.mark.asyncio
+    async def test_handle_reasoning_command_defaults_to_session_only(self, tmp_path, monkeypatch):
+        hermes_home = tmp_path / "hermes"
+        hermes_home.mkdir()
+        config_path = hermes_home / "config.yaml"
+        config_path.write_text("agent:\n  reasoning_effort: medium\n", encoding="utf-8")
+
+        monkeypatch.setattr(gateway_run, "_hermes_home", hermes_home)
+
+        runner = _make_runner()
+        event = _make_event("/reasoning high")
+        session_key = runner._session_key_for_source(event.source)
+
+        result = await runner._handle_reasoning_command(event)
+
+        saved = yaml.safe_load(config_path.read_text(encoding="utf-8"))
+        assert saved["agent"]["reasoning_effort"] == "medium"
+        assert runner._session_reasoning_overrides[session_key] == {"enabled": True, "effort": "high"}
+        assert runner._reasoning_config == {"enabled": True, "effort": "high"}
+        assert "session only" in result
+
+    @pytest.mark.asyncio
+    async def test_reasoning_global_clears_existing_session_override(self, tmp_path, monkeypatch):
+        hermes_home = tmp_path / "hermes"
+        hermes_home.mkdir()
+        config_path = hermes_home / "config.yaml"
+        config_path.write_text("agent:\n  reasoning_effort: medium\n", encoding="utf-8")
+
+        monkeypatch.setattr(gateway_run, "_hermes_home", hermes_home)
+
+        runner = _make_runner()
+        event = _make_event("/reasoning low --global")
+        session_key = runner._session_key_for_source(event.source)
+        runner._session_reasoning_overrides[session_key] = {"enabled": True, "effort": "xhigh"}
+
+        result = await runner._handle_reasoning_command(event)
+
+        saved = yaml.safe_load(config_path.read_text(encoding="utf-8"))
+        assert saved["agent"]["reasoning_effort"] == "low"
+        assert session_key not in runner._session_reasoning_overrides
+        assert "saved to config" in result
+
+    @pytest.mark.asyncio
+    async def test_reasoning_reset_clears_session_override_without_config_write(self, tmp_path, monkeypatch):
+        hermes_home = tmp_path / "hermes"
+        hermes_home.mkdir()
+        config_path = hermes_home / "config.yaml"
+        config_path.write_text("agent:\n  reasoning_effort: medium\n", encoding="utf-8")
+
+        monkeypatch.setattr(gateway_run, "_hermes_home", hermes_home)
+
+        runner = _make_runner()
+        event = _make_event("/reasoning reset")
+        session_key = runner._session_key_for_source(event.source)
+        runner._session_reasoning_overrides[session_key] = {"enabled": True, "effort": "xhigh"}
+
+        result = await runner._handle_reasoning_command(event)
+
+        saved = yaml.safe_load(config_path.read_text(encoding="utf-8"))
+        assert saved["agent"]["reasoning_effort"] == "medium"
+        assert session_key not in runner._session_reasoning_overrides
+        assert "cleared" in result
+
+    def test_resolve_session_reasoning_prefers_session_override(self, tmp_path, monkeypatch):
+        hermes_home = tmp_path / "hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text("agent:\n  reasoning_effort: low\n", encoding="utf-8")
+
+        monkeypatch.setattr(gateway_run, "_hermes_home", hermes_home)
+
+        runner = _make_runner()
+        source = _make_event("/reasoning").source
+        session_key = runner._session_key_for_source(source)
+        runner._session_reasoning_overrides[session_key] = {"enabled": True, "effort": "xhigh"}
+
+        assert runner._resolve_session_reasoning_config(source=source) == {"enabled": True, "effort": "xhigh"}
+
     def test_run_agent_reloads_reasoning_config_per_message(self, tmp_path, monkeypatch):
         hermes_home = tmp_path / "hermes"
         hermes_home.mkdir()
@@ -167,6 +249,56 @@ class TestReasoningCommand:
         assert _CapturingAgent.last_init is not None
         assert _CapturingAgent.last_init["reasoning_config"] == {"enabled": True, "effort": "low"}
 
+    def test_run_agent_prefers_session_reasoning_override(self, tmp_path, monkeypatch):
+        hermes_home = tmp_path / "hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text("agent:\n  reasoning_effort: low\n", encoding="utf-8")
+
+        monkeypatch.setattr(gateway_run, "_hermes_home", hermes_home)
+        monkeypatch.setattr(gateway_run, "_env_path", hermes_home / ".env")
+        monkeypatch.setattr(gateway_run, "load_dotenv", lambda *args, **kwargs: None)
+        monkeypatch.setattr(
+            gateway_run,
+            "_resolve_runtime_agent_kwargs",
+            lambda: {
+                "provider": "openrouter",
+                "api_mode": "chat_completions",
+                "base_url": "https://openrouter.ai/api/v1",
+                "api_key": "***",
+            },
+        )
+        fake_run_agent = types.ModuleType("run_agent")
+        fake_run_agent.AIAgent = _CapturingAgent
+        monkeypatch.setitem(sys.modules, "run_agent", fake_run_agent)
+
+        _CapturingAgent.last_init = None
+        runner = _make_runner()
+        session_key = "agent:main:local:dm"
+        runner._session_reasoning_overrides[session_key] = {"enabled": True, "effort": "high"}
+
+        source = SessionSource(
+            platform=Platform.LOCAL,
+            chat_id="cli",
+            chat_name="CLI",
+            chat_type="dm",
+            user_id="user-1",
+        )
+
+        result = asyncio.run(
+            runner._run_agent(
+                message="ping",
+                context_prompt="",
+                history=[],
+                source=source,
+                session_id="session-1",
+                session_key=session_key,
+            )
+        )
+
+        assert result["final_response"] == "ok"
+        assert _CapturingAgent.last_init is not None
+        assert _CapturingAgent.last_init["reasoning_config"] == {"enabled": True, "effort": "high"}
+
     def test_run_agent_includes_enabled_mcp_servers_in_gateway_toolsets(self, tmp_path, monkeypatch):
         hermes_home = tmp_path / "hermes"
         hermes_home.mkdir()
diff --git a/tests/gateway/test_session_model_override_routing.py b/tests/gateway/test_session_model_override_routing.py
index 340d01fdce..edada059da 100644
--- a/tests/gateway/test_session_model_override_routing.py
+++ b/tests/gateway/test_session_model_override_routing.py
@@ -54,6 +54,7 @@ def _make_runner():
     runner._background_tasks = set()
     runner._session_db = None
     runner._session_model_overrides = {}
+    runner._session_reasoning_overrides = {}
     runner._pending_model_notes = {}
     runner._pending_approvals = {}
     runner._agent_cache = {}
@@ -102,6 +103,7 @@ def test_run_agent_prefers_session_override_over_global_runtime(monkeypatch):
     )
     session_key = "agent:main:local:dm"
     runner._session_model_overrides[session_key] = _codex_override()
+    runner._session_reasoning_overrides[session_key] = {"enabled": True, "effort": "high"}
 
     result = asyncio.run(
         runner._run_agent(
@@ -121,6 +123,7 @@ def test_run_agent_prefers_session_override_over_global_runtime(monkeypatch):
     assert _CapturingAgent.last_init["api_mode"] == "codex_responses"
     assert _CapturingAgent.last_init["base_url"] == "https://chatgpt.com/backend-api/codex"
     assert _CapturingAgent.last_init["api_key"] == "***"
+    assert _CapturingAgent.last_init["reasoning_config"] == {"enabled": True, "effort": "high"}
 
 
 @pytest.mark.asyncio
@@ -149,6 +152,7 @@ async def test_background_task_prefers_session_override_over_global_runtime(monk
     )
     session_key = runner._session_key_for_source(source)
     runner._session_model_overrides[session_key] = _codex_override()
+    runner._session_reasoning_overrides[session_key] = {"enabled": True, "effort": "high"}
 
     await runner._run_background_task("say hello", source, "bg_test")
 
@@ -158,3 +162,4 @@ async def test_background_task_prefers_session_override_over_global_runtime(monk
     assert _CapturingAgent.last_init["api_mode"] == "codex_responses"
     assert _CapturingAgent.last_init["base_url"] == "https://chatgpt.com/backend-api/codex"
     assert _CapturingAgent.last_init["api_key"] == "***"
+    assert _CapturingAgent.last_init["reasoning_config"] == {"enabled": True, "effort": "high"}
diff --git a/tests/gateway/test_session_model_reset.py b/tests/gateway/test_session_model_reset.py
index 6529f3a11d..025487953d 100644
--- a/tests/gateway/test_session_model_reset.py
+++ b/tests/gateway/test_session_model_reset.py
@@ -1,4 +1,4 @@
-"""Tests that /new (and its /reset alias) clears the session-scoped model override."""
+"""Tests that /new (and its /reset alias) clears session-scoped overrides."""
 from datetime import datetime
 from types import SimpleNamespace
 from unittest.mock import AsyncMock, MagicMock
@@ -37,6 +37,7 @@ def _make_runner():
     runner._voice_mode = {}
     runner.hooks = SimpleNamespace(emit=AsyncMock(), loaded_hooks=False)
     runner._session_model_overrides = {}
+    runner._session_reasoning_overrides = {}
     runner._pending_model_notes = {}
     runner._background_tasks = set()
 
@@ -75,14 +76,16 @@ async def test_new_command_clears_session_model_override():
     runner._session_model_overrides[session_key] = {
         "model": "gpt-4o",
         "provider": "openai",
-        "api_key": "sk-test",
+        "api_key": "***",
         "base_url": "",
         "api_mode": "openai",
     }
+    runner._session_reasoning_overrides[session_key] = {"enabled": True, "effort": "high"}
 
     await runner._handle_reset_command(_make_event("/new"))
 
     assert session_key not in runner._session_model_overrides
+    assert session_key not in runner._session_reasoning_overrides
 
 
 @pytest.mark.asyncio
@@ -92,10 +95,12 @@ async def test_new_command_no_override_is_noop():
     session_key = build_session_key(_make_source())
 
     assert session_key not in runner._session_model_overrides
+    assert session_key not in runner._session_reasoning_overrides
 
     await runner._handle_reset_command(_make_event("/new"))
 
     assert session_key not in runner._session_model_overrides
+    assert session_key not in runner._session_reasoning_overrides
 
 
 @pytest.mark.asyncio
@@ -115,12 +120,16 @@ async def test_new_command_only_clears_own_session():
     runner._session_model_overrides[other_key] = {
         "model": "claude-sonnet-4-6",
         "provider": "anthropic",
-        "api_key": "sk-ant-test",
+        "api_key": "***",
         "base_url": "",
         "api_mode": "anthropic",
     }
+    runner._session_reasoning_overrides[session_key] = {"enabled": True, "effort": "high"}
+    runner._session_reasoning_overrides[other_key] = {"enabled": True, "effort": "low"}
 
     await runner._handle_reset_command(_make_event("/new"))
 
     assert session_key not in runner._session_model_overrides
     assert other_key in runner._session_model_overrides
+    assert session_key not in runner._session_reasoning_overrides
+    assert other_key in runner._session_reasoning_overrides