diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9c10538..fe356ed 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Hermes Web UI -- Changelog
 
+## [v0.50.133] — 2026-04-21
+
+### Added
+- **`/reasoning show` and `/reasoning hide` slash commands** — toggle thinking/reasoning block visibility directly from the chat composer, matching the Hermes CLI/TUI parity. `/reasoning show` reveals all thinking cards (live and historical) and persists the preference; `/reasoning hide` collapses them. `/reasoning` with no args shows current state. The `show|hide` options now appear in autocomplete alongside the existing `low|medium|high` effort levels. The `show_thinking` setting is persisted via `/api/settings` so the preference survives page reloads. Closes #461 (partial — effort level routing to agent is a follow-up). (#812)
+
 ## [v0.50.132] — 2026-04-21
 
 ### Fixed
diff --git a/api/config.py b/api/config.py
index 9c30a46..3bf5ba9 100644
--- a/api/config.py
+++ b/api/config.py
@@ -761,6 +761,99 @@ def get_effective_default_model(config_data: dict | None = None) -> str:
     return default_model
 
 
+# ── Reasoning config (CLI parity for /reasoning) ─────────────────────────────
+# Mirrors hermes_constants.parse_reasoning_effort so WebUI can validate without
+# importing from the agent tree (which may not be installed).  Any drift here
+# will show up in the shared test suite since both sides accept the same set.
+VALID_REASONING_EFFORTS = ("minimal", "low", "medium", "high", "xhigh")
+
+
+def parse_reasoning_effort(effort):
+    """Parse an effort level into the dict the agent expects.
+
+    Returns None when *effort* is empty or unrecognised (caller interprets as
+    "use default"), ``{"enabled": False}`` for ``"none"``, and
+    ``{"enabled": True, "effort": <level>}`` for any of
+    ``VALID_REASONING_EFFORTS``.
+    """
+    if not effort or not str(effort).strip():
+        return None
+    eff = str(effort).strip().lower()
+    if eff == "none":
+        return {"enabled": False}
+    if eff in VALID_REASONING_EFFORTS:
+        return {"enabled": True, "effort": eff}
+    return None
+
+
+def get_reasoning_status() -> dict:
+    """Return current reasoning configuration from the active profile's
+    config.yaml — the same source of truth the CLI reads from.
+
+    Keys:
+      - show_reasoning: bool — from ``display.show_reasoning`` (default True)
+      - reasoning_effort: str — from ``agent.reasoning_effort`` ('' = default)
+    """
+    config_data = _load_yaml_config_file(_get_config_path())
+    display_cfg = config_data.get("display") or {}
+    agent_cfg = config_data.get("agent") or {}
+    show_raw = display_cfg.get("show_reasoning") if isinstance(display_cfg, dict) else None
+    effort_raw = agent_cfg.get("reasoning_effort") if isinstance(agent_cfg, dict) else None
+    return {
+        # Match CLI default (True if unset in config.yaml)
+        "show_reasoning": bool(show_raw) if isinstance(show_raw, bool) else True,
+        "reasoning_effort": str(effort_raw or "").strip().lower(),
+    }
+
+
+def set_reasoning_display(show: bool) -> dict:
+    """Persist ``display.show_reasoning`` to the active profile's config.yaml.
+
+    Mirrors CLI ``/reasoning show|hide``: writes the same key that the CLI
+    writes, so the preference is shared across the WebUI and the terminal
+    REPL for the same profile.
+    """
+    config_path = _get_config_path()
+    with _cfg_lock:
+        config_data = _load_yaml_config_file(config_path)
+        display_cfg = config_data.get("display")
+        if not isinstance(display_cfg, dict):
+            display_cfg = {}
+        display_cfg["show_reasoning"] = bool(show)
+        config_data["display"] = display_cfg
+        _save_yaml_config_file(config_path, config_data)
+    reload_config()
+    return get_reasoning_status()
+
+
+def set_reasoning_effort(effort: str) -> dict:
+    """Persist ``agent.reasoning_effort`` to the active profile's config.yaml.
+
+    Mirrors CLI ``/reasoning <level>``: same key, same valid values
+    (``none`` | ``minimal`` | ``low`` | ``medium`` | ``high`` | ``xhigh``).
+    Raises ``ValueError`` on an unrecognised level so callers can return 400.
+    """
+    raw = str(effort or "").strip().lower()
+    if not raw:
+        raise ValueError("effort is required")
+    if raw != "none" and raw not in VALID_REASONING_EFFORTS:
+        raise ValueError(
+            f"Unknown reasoning effort '{effort}'. "
+            f"Valid: none, {', '.join(VALID_REASONING_EFFORTS)}."
+        )
+    config_path = _get_config_path()
+    with _cfg_lock:
+        config_data = _load_yaml_config_file(config_path)
+        agent_cfg = config_data.get("agent")
+        if not isinstance(agent_cfg, dict):
+            agent_cfg = {}
+        agent_cfg["reasoning_effort"] = raw
+        config_data["agent"] = agent_cfg
+        _save_yaml_config_file(config_path, config_data)
+    reload_config()
+    return get_reasoning_status()
+
+
 def set_hermes_default_model(model_id: str) -> dict:
     """Persist the Hermes default model in config.yaml and reload runtime config."""
     selected_model = str(model_id or "").strip()
@@ -1381,6 +1474,7 @@ _SETTINGS_DEFAULTS = {
     ),  # display name for the assistant
     "sound_enabled": False,  # play notification sound when assistant finishes
     "notifications_enabled": False,  # browser notification when tab is in background
+    "show_thinking": True,  # show/hide thinking/reasoning blocks in chat view
     "sidebar_density": "compact",  # compact | detailed
     "password_hash": None,  # PBKDF2-HMAC-SHA256 hash; None = auth disabled
 }
@@ -1491,6 +1585,7 @@ _SETTINGS_BOOL_KEYS = {
     "check_for_updates",
     "sound_enabled",
     "notifications_enabled",
+    "show_thinking",
 }
 # Language codes are validated as short alphanumeric BCP-47-like tags (e.g. 'en', 'zh', 'fr')
 _SETTINGS_LANG_RE = __import__("re").compile(r"^[a-zA-Z]{2,10}(-[a-zA-Z0-9]{2,8})?$")
diff --git a/api/routes.py b/api/routes.py
index 83082b6..742b42e 100644
--- a/api/routes.py
+++ b/api/routes.py
@@ -48,6 +48,9 @@ from api.config import (
     load_settings,
     save_settings,
     set_hermes_default_model,
+    get_reasoning_status,
+    set_reasoning_display,
+    set_reasoning_effort,
 )
 from api.helpers import (
     require,
@@ -557,6 +560,12 @@ def handle_get(handler, parsed) -> bool:
             pass
         return j(handler, settings)
 
+    if parsed.path == "/api/reasoning":
+        # Current reasoning config (shared source of truth with the CLI —
+        # reads display.show_reasoning and agent.reasoning_effort from
+        # the active profile's config.yaml).
+        return j(handler, get_reasoning_status())
+
     if parsed.path == "/api/onboarding/status":
         return j(handler, get_onboarding_status())
 
@@ -899,6 +908,32 @@ def handle_post(handler, parsed) -> bool:
         except RuntimeError as e:
             return bad(handler, str(e), 500)
 
+    if parsed.path == "/api/reasoning":
+        # CLI-parity /reasoning handler — writes to the same config.yaml keys
+        # the CLI uses (display.show_reasoning, agent.reasoning_effort) so a
+        # preference set via WebUI is honoured in the terminal REPL and vice
+        # versa.  Body is one of:
+        #   {"display": "show"|"hide"|"on"|"off"}   → display.show_reasoning
+        #   {"effort":  "none"|"minimal"|"low"|"medium"|"high"|"xhigh"}
+        #                                            → agent.reasoning_effort
+        try:
+            display = body.get("display")
+            effort = body.get("effort")
+            if display is not None:
+                flag = str(display).strip().lower()
+                if flag in ("show", "on", "true", "1"):
+                    return j(handler, set_reasoning_display(True))
+                if flag in ("hide", "off", "false", "0"):
+                    return j(handler, set_reasoning_display(False))
+                return bad(handler, f"display must be show|hide|on|off (got '{display}')")
+            if effort is not None:
+                return j(handler, set_reasoning_effort(effort))
+            return bad(handler, "reasoning: must supply 'display' or 'effort'")
+        except ValueError as e:
+            return bad(handler, str(e))
+        except RuntimeError as e:
+            return bad(handler, str(e), 500)
+
     if parsed.path == "/api/sessions/cleanup":
         return _handle_sessions_cleanup(handler, body, zero_only=False)
 
diff --git a/api/streaming.py b/api/streaming.py
index 7c2f623..59622e5 100644
--- a/api/streaming.py
+++ b/api/streaming.py
@@ -1100,6 +1100,18 @@ def _run_agent_streaming(session_id, msg_text, model, workspace, stream_id, atta
             import inspect as _inspect
             _agent_params = set(_inspect.signature(_AIAgent.__init__).parameters)
 
+            # CLI-parity reasoning effort: read agent.reasoning_effort from the
+            # active profile's config.yaml (the same key the CLI writes via
+            # `/reasoning <level>`) and hand the parsed dict to AIAgent.  When
+            # the key is absent or invalid, pass None → agent uses its default.
+            try:
+                from api.config import parse_reasoning_effort as _parse_reff
+                _effort_cfg = _cfg.cfg.get('agent', {}) if isinstance(_cfg.cfg, dict) else {}
+                _effort_raw = _effort_cfg.get('reasoning_effort') if isinstance(_effort_cfg, dict) else None
+                _reasoning_config = _parse_reff(_effort_raw)
+            except Exception:
+                _reasoning_config = None
+
             _agent_kwargs = dict(
                 model=resolved_model,
                 provider=resolved_provider,
@@ -1120,6 +1132,10 @@ def _run_agent_streaming(session_id, msg_text, model, workspace, stream_id, atta
                     )
                 ),
             )
+            # reasoning_config has been an AIAgent param for several releases,
+            # but guard defensively to avoid TypeError on an older agent build.
+            if 'reasoning_config' in _agent_params and _reasoning_config is not None:
+                _agent_kwargs['reasoning_config'] = _reasoning_config
             # Params added in newer hermes-agent — skip if not supported
             if 'api_mode' in _agent_params:
                 _agent_kwargs['api_mode'] = _rt.get('api_mode')
diff --git a/static/boot.js b/static/boot.js
index 62de57d..aa36e1e 100644
--- a/static/boot.js
+++ b/static/boot.js
@@ -764,6 +764,7 @@ function applyBotName(){
     window._showCliSessions=!!s.show_cli_sessions;
     window._soundEnabled=!!s.sound_enabled;
     window._notificationsEnabled=!!s.notifications_enabled;
+    window._showThinking=s.show_thinking!==false;
     window._sidebarDensity=(s.sidebar_density==='detailed'?'detailed':'compact');
     window._botName=s.bot_name||'Hermes';
     const appearance=_normalizeAppearance(s.theme,s.skin);
@@ -785,6 +786,7 @@ function applyBotName(){
     window._showCliSessions=false;
     window._soundEnabled=false;
     window._notificationsEnabled=false;
+    window._showThinking=true;
     window._sidebarDensity='compact';
     window._botName='Hermes';
     _bootSettings={check_for_updates:false};
diff --git a/static/commands.js b/static/commands.js
index e036311..2cbe952 100644
--- a/static/commands.js
+++ b/static/commands.js
@@ -20,12 +20,12 @@ const COMMANDS=[
   {name:'undo',      desc:t('cmd_undo'),     fn:cmdUndo},
   {name:'status',    desc:t('cmd_status'),   fn:cmdStatus},
   {name:'voice',     desc:t('cmd_voice'),    fn:cmdVoice},
+  {name:'reasoning', desc:t('cmd_reasoning'), fn:cmdReasoning, arg:'show|hide|none|minimal|low|medium|high|xhigh', subArgs:['show','hide','none','minimal','low','medium','high','xhigh']},
 ];
 
 const SLASH_SUBARG_SOURCES={
   model:{desc:t('cmd_model'), subArgs:'models'},
   personality:{desc:t('cmd_personality'), subArgs:'personalities'},
-  reasoning:{desc:'Set reasoning effort', subArgs:['low','medium','high']},
 };
 
 function parseCommand(text){
@@ -41,8 +41,10 @@ function executeCommand(text){
   if(!parsed)return false;
   const cmd=COMMANDS.find(c=>c.name===parsed.name);
   if(!cmd)return false;
-  cmd.fn(parsed.args);
-  return true;
+  // A handler may return `false` to opt out of interception — e.g. /reasoning
+  // with an effort level falls through so the agent's own handler sees it,
+  // preserving the pre-existing pass-through behaviour for that subcommand.
+  return cmd.fn(parsed.args) !== false;
 }
 
 function getMatchingCommands(prefix){
@@ -572,6 +574,56 @@ async function cmdStatus(){
     renderMessages();
   }catch(e){showToast(t('status_load_failed')+e.message);}
 }
+function cmdReasoning(args){
+  const arg=(args||'').trim().toLowerCase();
+  const BRAIN='\uD83E\uDDE0';
+  // Matches hermes_constants.VALID_REASONING_EFFORTS + 'none' (CLI parity).
+  const EFFORTS=['none','minimal','low','medium','high','xhigh'];
+  // Shared status renderer used by the no-args branch and as a fallback.
+  function _fmtStatus(st){
+    const vis=(st && st.show_reasoning===false)?'off':'on';
+    const eff=(st && st.reasoning_effort)||'default';
+    return BRAIN+' Reasoning effort: '+eff+' \u00B7 display: '+vis
+      +'  |  /reasoning show|hide|none|minimal|low|medium|high|xhigh';
+  }
+  if(!arg){
+    // Status — read from the same config.yaml keys the CLI uses.
+    api('/api/reasoning').then(function(st){showToast(_fmtStatus(st));})
+      .catch(function(){showToast(BRAIN+' /reasoning — status unavailable');});
+    return true;
+  }
+  if(arg==='show'||arg==='on'||arg==='hide'||arg==='off'){
+    const on=(arg==='show'||arg==='on');
+    // Update the UI render gate immediately for responsiveness.
+    window._showThinking=on;
+    if(typeof renderMessages==='function') renderMessages();
+    // Persist via /api/reasoning → config.yaml display.show_reasoning
+    // (CLI reads the same key).  Also mirror into WebUI settings.json
+    // show_thinking so boot.js picks it up on reload without hitting
+    // /api/reasoning on every page load.
+    api('/api/reasoning',{method:'POST',body:JSON.stringify({display:arg})}).catch(function(){});
+    api('/api/settings',{method:'POST',body:JSON.stringify({show_thinking:on})}).catch(function(){});
+    showToast(BRAIN+' Thinking blocks: '+(on?'on':'off')+' (saved)');
+    return true;
+  }
+  if(EFFORTS.includes(arg)){
+    // Persist via /api/reasoning → config.yaml agent.reasoning_effort.
+    // Takes effect on the NEXT session/turn (agent re-reads config at
+    // construction time), matching CLI semantics where `/reasoning high`
+    // also forces an agent re-init.
+    api('/api/reasoning',{method:'POST',body:JSON.stringify({effort:arg})})
+      .then(function(st){
+        const eff=(st && st.reasoning_effort)||arg;
+        showToast(BRAIN+' Reasoning effort set to '+eff+' (saved; applies to next turn)');
+      })
+      .catch(function(e){
+        showToast(BRAIN+' Failed to set effort: '+(e && e.message ? e.message : arg));
+      });
+    return true;
+  }
+  showToast('Unknown argument: '+arg+' \u2014 use show|hide|'+EFFORTS.join('|'));
+  return true;
+}
 function cmdVoice(){
   const mic=document.getElementById('btnMic');
   if(mic&&mic.style.display!=='none'&&!mic.disabled){try{mic.click();return;}catch(_){}}
diff --git a/static/i18n.js b/static/i18n.js
index 9c95fb0..bdeec05 100644
--- a/static/i18n.js
+++ b/static/i18n.js
@@ -195,6 +195,7 @@ const LOCALES = {
     settings_label_language: 'Language',
     settings_label_token_usage: 'Show token usage',
     settings_label_sidebar_density: 'Sidebar density',
+    cmd_reasoning: 'Toggle thinking block visibility (show/hide) or set effort level',
     settings_label_cli_sessions: 'Show agent sessions',
     settings_label_sync_insights: 'Sync to insights',
     settings_label_check_updates: 'Check for updates',
@@ -626,6 +627,7 @@ const LOCALES = {
     settings_label_language: 'Язык',
     settings_label_token_usage: 'Показывать использование токенов',
     settings_label_sidebar_density: 'Плотность боковой панели',
+    cmd_reasoning: 'Toggle thinking block visibility (show/hide) or set effort level',
     settings_label_cli_sessions: 'Показывать сеансы агента',
     settings_label_sync_insights: 'Синхронизировать с Insights',
     settings_label_check_updates: 'Проверять обновления',
@@ -1085,6 +1087,7 @@ const LOCALES = {
     settings_label_language: 'Idioma',
     settings_label_token_usage: 'Mostrar uso de tokens',
     settings_label_sidebar_density: 'Densidad de la barra lateral',
+    cmd_reasoning: 'Toggle thinking block visibility (show/hide) or set effort level',
     settings_label_cli_sessions: 'Mostrar sesiones de CLI',
     settings_label_sync_insights: 'Sincronizar con insights',
     settings_label_check_updates: 'Buscar actualizaciones',
@@ -1516,6 +1519,7 @@ const LOCALES = {
     settings_label_language: 'Sprache',
     settings_label_token_usage: 'Token-Verbrauch anzeigen',
     settings_label_sidebar_density: 'Seitenleistendichte',
+    cmd_reasoning: 'Toggle thinking block visibility (show/hide) or set effort level',
     settings_label_cli_sessions: 'Agent-Sitzungen anzeigen',
     settings_label_sync_insights: 'Mit Insights synchronisieren',
     settings_label_check_updates: 'Nach Updates suchen',
@@ -1748,6 +1752,7 @@ const LOCALES = {
     settings_label_language: '\u8bed\u8a00',
     settings_label_token_usage: '\u663e\u793a token \u7528\u91cf',
     settings_label_sidebar_density: '侧边栏密度',
+    cmd_reasoning: 'Toggle thinking block visibility (show/hide) or set effort level',
     settings_label_cli_sessions: '\u663e\u793a CLI \u4f1a\u8bdd',
     settings_label_sync_insights: '\u540c\u6b65\u5230 insights',
     settings_label_check_updates: '\u68c0\u67e5\u66f4\u65b0',
@@ -2163,6 +2168,7 @@ const LOCALES = {
     settings_label_language: '\u8a9d\u8a00',
     settings_label_token_usage: '\u986f\u793a token \u7528\u91cf',
     settings_label_sidebar_density: '側邊欄密度',
+    cmd_reasoning: 'Toggle thinking block visibility (show/hide) or set effort level',
     settings_label_cli_sessions: '\u986f\u793a CLI \u6703\u8a71',
     settings_label_sync_insights: '\u540c\u6b65\u5230 insights',
     settings_label_check_updates: '\u6aa2\u67e5\u66f4\u65b0',
diff --git a/static/messages.js b/static/messages.js
index 38818fd..cbff2d7 100644
--- a/static/messages.js
+++ b/static/messages.js
@@ -295,6 +295,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
     return {thinkingText:'', displayText:raw, inThinking:false};
   }
   function _renderLiveThinking(parsed){
+    if(window._showThinking===false){removeThinking();return;}
     const text=(parsed&&parsed.thinkingText)||'';
     if(text||(parsed&&parsed.inThinking)){
       if(typeof updateThinking==='function') updateThinking(text||'Thinking…');
diff --git a/static/panels.js b/static/panels.js
index 514e257..a18aae1 100644
--- a/static/panels.js
+++ b/static/panels.js
@@ -1272,6 +1272,7 @@ async function loadSettingsPanel(){
     if(soundCb){soundCb.checked=!!settings.sound_enabled;soundCb.addEventListener('change',_markSettingsDirty,{once:false});}
     const notifCb=$('settingsNotificationsEnabled');
     if(notifCb){notifCb.checked=!!settings.notifications_enabled;notifCb.addEventListener('change',_markSettingsDirty,{once:false});}
+    // show_thinking has no settings panel checkbox — controlled via /reasoning show|hide
     const sidebarDensitySel=$('settingsSidebarDensity');
     if(sidebarDensitySel){
       sidebarDensitySel.value=settings.sidebar_density==='detailed'?'detailed':'compact';
@@ -1309,6 +1310,7 @@ function _applySavedSettingsUi(saved, body, opts){
   window._showCliSessions=showCliSessions;
   window._soundEnabled=body.sound_enabled;
   window._notificationsEnabled=body.notifications_enabled;
+  window._showThinking=body.show_thinking!==false;
   window._sidebarDensity=sidebarDensity==='detailed'?'detailed':'compact';
   window._botName=body.bot_name||'Hermes';
   if(typeof applyBotName==='function') applyBotName();
@@ -1353,6 +1355,7 @@ async function saveSettings(andClose){
   body.check_for_updates=!!($('settingsCheckUpdates')||{}).checked;
   body.sound_enabled=!!($('settingsSoundEnabled')||{}).checked;
   body.notifications_enabled=!!($('settingsNotificationsEnabled')||{}).checked;
+  body.show_thinking=window._showThinking!==false;
   body.sidebar_density=sidebarDensity;
   const botName=(($('settingsBotName')||{}).value||'').trim();
   body.bot_name=botName||'Hermes';
diff --git a/static/ui.js b/static/ui.js
index 1256782..93dc52f 100644
--- a/static/ui.js
+++ b/static/ui.js
@@ -1573,7 +1573,7 @@ function renderMessages(){
       seg.setAttribute('data-live-assistant','1');
     }
     if(_ERR_MSG_RE.test(String(content||'').trim())) seg.dataset.error='1';
-    if(thinkingText) seg.insertAdjacentHTML('beforeend', _thinkingCardHtml(thinkingText));
+    if(thinkingText&&window._showThinking!==false) seg.insertAdjacentHTML('beforeend', _thinkingCardHtml(thinkingText));
     const hasVisibleBody=!!(String(content||'').trim()||filesHtml);
     if(hasVisibleBody){
       seg.insertAdjacentHTML('beforeend', `${filesHtml}<div class="msg-body">${bodyHtml}</div>${footHtml}`);
diff --git a/tests/test_issue632.py b/tests/test_issue632.py
index dde8b73..983b6bf 100644
--- a/tests/test_issue632.py
+++ b/tests/test_issue632.py
@@ -18,13 +18,19 @@ BOOT_JS = (REPO_ROOT / "static" / "boot.js").read_text(encoding="utf-8")
 STYLE_CSS = (REPO_ROOT / "static" / "style.css").read_text(encoding="utf-8")
 
 
-def test_subarg_registry_exists_without_promoting_reasoning_to_builtin():
+def test_subarg_registry_exists_and_reasoning_is_promoted_to_builtin():
+    # SLASH_SUBARG_SOURCES still exists for model and personality
     assert "const SLASH_SUBARG_SOURCES=" in COMMANDS_JS
-    assert "reasoning:{desc:'Set reasoning effort', subArgs:['low','medium','high']}" in COMMANDS_JS
-    assert "{name:'reasoning'" not in COMMANDS_JS, \
-        "/reasoning suggestions must not register as a local built-in command"
-    assert "source:'subarg-command'" in COMMANDS_JS, \
-        "top-level autocomplete should still surface subarg-only commands like /reasoning"
+    # /reasoning is now a proper builtin command with a fn: handler (cmdReasoning)
+    # so it is in the COMMANDS array, not SLASH_SUBARG_SOURCES
+    assert "{name:'reasoning'" in COMMANDS_JS, \
+        "/reasoning must be registered as a local built-in command with fn: handler"
+    assert "fn:cmdReasoning" in COMMANDS_JS, \
+        "/reasoning entry must reference cmdReasoning function"
+    assert "function cmdReasoning" in COMMANDS_JS, \
+        "cmdReasoning function must be defined"
+    # source:'subarg-command' is still used for model/personality in SLASH_SUBARG_SOURCES
+    assert "source:'subarg-command'" in COMMANDS_JS
 
 
 def test_model_and_personality_subargs_load_from_existing_apis():
diff --git a/tests/test_reasoning_show_hide.py b/tests/test_reasoning_show_hide.py
new file mode 100644
index 0000000..7591aaf
--- /dev/null
+++ b/tests/test_reasoning_show_hide.py
@@ -0,0 +1,397 @@
+"""Tests for /reasoning show|hide slash command and show_thinking setting.
+
+Covers:
+  - show_thinking in _SETTINGS_DEFAULTS and _SETTINGS_BOOL_KEYS (api/config.py)
+  - window._showThinking initialised in boot.js (settings and fallback paths)
+  - window._showThinking guard in ui.js renderMessages thinking card
+  - _renderLiveThinking guard in messages.js
+  - cmdReasoning function present in commands.js with show/hide/effort handling
+  - /reasoning in COMMANDS array (not just SLASH_SUBARG_SOURCES)
+  - show|hide present as subArgs in COMMANDS entry
+"""
+
+import pathlib
+import re
+
+REPO = pathlib.Path(__file__).parent.parent
+
+
+def read(rel):
+    return (REPO / rel).read_text(encoding='utf-8')
+
+
+# ── api/config.py ─────────────────────────────────────────────────────────────
+
+class TestShowThinkingConfig:
+    """show_thinking must appear in defaults and bool keys."""
+
+    def test_show_thinking_in_defaults(self):
+        src = read('api/config.py')
+        assert '"show_thinking": True' in src, (
+            "show_thinking must be True in _SETTINGS_DEFAULTS"
+        )
+
+    def test_show_thinking_in_bool_keys(self):
+        src = read('api/config.py')
+        assert '"show_thinking"' in src
+        # Find the _SETTINGS_BOOL_KEYS set and confirm show_thinking is in it
+        m = re.search(r'_SETTINGS_BOOL_KEYS\s*=\s*\{([^}]+)\}', src, re.DOTALL)
+        assert m, "_SETTINGS_BOOL_KEYS not found"
+        assert 'show_thinking' in m.group(1), (
+            "show_thinking must be in _SETTINGS_BOOL_KEYS"
+        )
+
+
+# ── static/boot.js ────────────────────────────────────────────────────────────
+
+class TestBootJsShowThinking:
+    """window._showThinking must be set in both the settings and fallback paths."""
+
+    def test_settings_path_initialises_show_thinking(self):
+        src = read('static/boot.js')
+        # Must read from the settings object, defaulting true when absent
+        assert 'window._showThinking=s.show_thinking!==false' in src, (
+            "boot.js must initialise _showThinking from settings (default true)"
+        )
+
+    def test_fallback_path_initialises_show_thinking_true(self):
+        src = read('static/boot.js')
+        assert 'window._showThinking=true' in src, (
+            "boot.js fallback path must default _showThinking to true"
+        )
+
+
+# ── static/ui.js ──────────────────────────────────────────────────────────────
+
+class TestUiJsThinkingGate:
+    """Historical thinking cards must be gated by window._showThinking."""
+
+    def test_thinking_card_gated_in_render_messages(self):
+        src = read('static/ui.js')
+        assert 'window._showThinking!==false' in src, (
+            "ui.js must gate thinkingCardHtml on window._showThinking"
+        )
+        # The guard must be on the same line as _thinkingCardHtml insertion
+        lines = src.splitlines()
+        for line in lines:
+            if '_thinkingCardHtml' in line and 'insertAdjacentHTML' in line:
+                assert 'window._showThinking' in line, (
+                    f"thinking card insertion must be gated: {line.strip()}"
+                )
+                break
+
+
+# ── static/messages.js ────────────────────────────────────────────────────────
+
+class TestMessagesJsLiveThinkingGate:
+    """Live streaming thinking card must be hidden when _showThinking is false."""
+
+    def test_live_thinking_gated(self):
+        src = read('static/messages.js')
+        assert 'window._showThinking===false' in src, (
+            "messages.js _renderLiveThinking must early-return when _showThinking is false"
+        )
+        # Guard must be inside _renderLiveThinking
+        m = re.search(r'function _renderLiveThinking\(.*?\{(.*?)^\s*\}',
+                      src, re.DOTALL | re.MULTILINE)
+        assert m, "_renderLiveThinking not found"
+        assert 'window._showThinking' in m.group(1)
+
+
+# ── static/commands.js ────────────────────────────────────────────────────────
+
+class TestReasoningCommand:
+    """cmdReasoning must be wired into COMMANDS with show/hide subArgs."""
+
+    def test_reasoning_in_commands_array(self):
+        src = read('static/commands.js')
+        # Must appear in COMMANDS array (not just SLASH_SUBARG_SOURCES)
+        m = re.search(r'const COMMANDS\s*=\s*\[(.*?)\];', src, re.DOTALL)
+        assert m, "COMMANDS array not found"
+        commands_block = m.group(1)
+        assert 'reasoning' in commands_block, (
+            "/reasoning must be in the COMMANDS array with a fn: handler"
+        )
+        assert 'fn:cmdReasoning' in commands_block or "fn: cmdReasoning" in commands_block, (
+            "/reasoning entry must reference cmdReasoning"
+        )
+
+    def test_reasoning_subargs_include_show_hide(self):
+        src = read('static/commands.js')
+        m = re.search(r'const COMMANDS\s*=\s*\[(.*?)\];', src, re.DOTALL)
+        assert m
+        commands_block = m.group(1)
+        # Find the reasoning entry
+        rm = re.search(r"\{name:'reasoning'.*?\}", commands_block, re.DOTALL)
+        assert rm, "reasoning entry not found in COMMANDS"
+        entry = rm.group(0)
+        assert 'show' in entry, "subArgs must include 'show'"
+        assert 'hide' in entry, "subArgs must include 'hide'"
+
+    def test_reasoning_not_only_in_subarg_sources(self):
+        src = read('static/commands.js')
+        # It's fine if SLASH_SUBARG_SOURCES is empty or doesn't have reasoning
+        # (reasoning moved to COMMANDS with a real fn)
+        m = re.search(r'const SLASH_SUBARG_SOURCES\s*=\s*\{(.*?)\};', src, re.DOTALL)
+        if m:
+            subarg_block = m.group(1)
+            assert 'reasoning' not in subarg_block, (
+                "reasoning must not remain in SLASH_SUBARG_SOURCES once it has a fn: handler"
+            )
+
+    def test_cmd_reasoning_function_exists(self):
+        src = read('static/commands.js')
+        assert 'function cmdReasoning' in src, (
+            "cmdReasoning function must be defined"
+        )
+
+    def test_cmd_reasoning_handles_show(self):
+        src = read('static/commands.js')
+        m = re.search(r'function cmdReasoning\(.*?\n\}', src, re.DOTALL)
+        assert m, "cmdReasoning not found"
+        fn = m.group(0)
+        # Handler must write to the UI render gate (assignment may use a
+        # boolean literal or a locally-computed variable) and call renderMessages.
+        assert re.search(r'window\._showThinking\s*=\s*(?:true|on)\b', fn), (
+            "cmdReasoning show branch must assign true/on to window._showThinking"
+        )
+        assert 'renderMessages' in fn, (
+            "show/hide branch must call renderMessages()"
+        )
+        # Persistence: POST to /api/reasoning (CLI-shared config.yaml) AND
+        # /api/settings (boot.js mirror).
+        assert "api('/api/reasoning'" in fn, (
+            "show/hide branch must POST to /api/reasoning so config.yaml "
+            "display.show_reasoning is updated (CLI parity)"
+        )
+        assert 'show_thinking' in fn, (
+            "show/hide branch must also mirror show_thinking into "
+            "WebUI settings.json for boot.js hydration"
+        )
+
+    def test_cmd_reasoning_handles_hide(self):
+        src = read('static/commands.js')
+        m = re.search(r'function cmdReasoning\(.*?\n\}', src, re.DOTALL)
+        assert m
+        fn = m.group(0)
+        # The hide branch shares logic with show via a computed `on` variable;
+        # the combined branch must test for both show|on and hide|off.
+        assert "arg==='hide'" in fn, "hide branch missing"
+        assert "arg==='off'" in fn, "off alias missing"
+
+    def test_cmd_reasoning_i18n_key_exists(self):
+        i18n = read('static/i18n.js')
+        assert 'cmd_reasoning' in i18n, (
+            "i18n.js must define the cmd_reasoning key"
+        )
+
+    def test_cmd_reasoning_posts_api_endpoints_not_gets(self):
+        """Regression: the api() helper spreads its 2nd arg into fetch(), so
+        passing a plain options object without method:'POST' silently becomes
+        a GET and the update is dropped.  Every mutating call inside
+        cmdReasoning (/api/reasoning, /api/settings) must be a proper POST."""
+        src = read('static/commands.js')
+        m = re.search(r'function cmdReasoning\(.*?\n\}', src, re.DOTALL)
+        assert m
+        fn = m.group(0)
+        # Every write call — /api/reasoning and /api/settings — must be a POST.
+        write_calls = re.findall(
+            r"api\('/api/(?:reasoning|settings)'\s*,[^)]*\)", fn
+        )
+        assert write_calls, "cmdReasoning must POST to /api/reasoning or /api/settings"
+        for call in write_calls:
+            assert "method:'POST'" in call or 'method: "POST"' in call, (
+                f"write call missing method:'POST' — would fall through "
+                f"to GET and silently drop the update: {call}"
+            )
+            assert 'JSON.stringify' in call, (
+                f"write call missing JSON body: {call}"
+            )
+
+    def test_cmd_reasoning_routes_effort_through_api_reasoning(self):
+        """Effort levels (none|minimal|low|medium|high|xhigh) must POST to
+        /api/reasoning so the agent's config.yaml agent.reasoning_effort is
+        updated — the same key the CLI writes via `/reasoning <level>`.
+        Previous design stored in a dead client variable, which did nothing."""
+        src = read('static/commands.js')
+        m = re.search(r'function cmdReasoning\(.*?\n\}', src, re.DOTALL)
+        assert m
+        fn = m.group(0)
+        assert "api('/api/reasoning'" in fn, (
+            "cmdReasoning must POST effort levels to /api/reasoning so "
+            "config.yaml agent.reasoning_effort is updated (CLI parity)"
+        )
+        assert "'effort:'" in fn or 'effort:arg' in fn or 'effort: arg' in fn, (
+            "effort-level branch must send {effort: arg} to /api/reasoning"
+        )
+        # Must NOT still hold a dead local-only variable for effort.
+        assert '_reasoningEffort=' not in fn, (
+            "cmdReasoning must not keep a dead client-side _reasoningEffort "
+            "(effort now round-trips through /api/reasoning → config.yaml)"
+        )
+
+    def test_cmd_reasoning_routes_display_through_api_reasoning(self):
+        """show|hide|on|off must POST to /api/reasoning (config.yaml
+        display.show_reasoning — the CLI's key) in addition to mirroring
+        into WebUI settings.json for boot.js hydration."""
+        src = read('static/commands.js')
+        m = re.search(r'function cmdReasoning\(.*?\n\}', src, re.DOTALL)
+        assert m
+        fn = m.group(0)
+        assert 'display:arg' in fn or 'display: arg' in fn or "'display'" in fn, (
+            "show|hide branch must send {display: arg} to /api/reasoning so "
+            "config.yaml display.show_reasoning matches the CLI's source"
+        )
+
+    def test_cmd_reasoning_supports_all_cli_effort_levels(self):
+        """The effort-level set must match hermes_constants.VALID_REASONING_EFFORTS
+        + 'none' — i.e. the exact set the CLI accepts in /reasoning."""
+        src = read('static/commands.js')
+        m = re.search(r'function cmdReasoning\(.*?\n\}', src, re.DOTALL)
+        assert m
+        fn = m.group(0)
+        for level in ('none', 'minimal', 'low', 'medium', 'high', 'xhigh'):
+            assert f"'{level}'" in fn, (
+                f"cmdReasoning must accept '{level}' (CLI parity with "
+                f"hermes_constants.parse_reasoning_effort)"
+            )
+
+    def test_reasoning_subargs_match_cli_levels(self):
+        """Autocomplete subArgs must expose every CLI effort level + show/hide."""
+        src = read('static/commands.js')
+        m = re.search(r"\{name:'reasoning'[^}]*\}", src, re.DOTALL)
+        assert m, "reasoning COMMANDS entry not found"
+        entry = m.group(0)
+        for suggestion in (
+            'show', 'hide', 'none', 'minimal', 'low', 'medium', 'high', 'xhigh'
+        ):
+            assert f"'{suggestion}'" in entry, (
+                f"reasoning subArgs must include '{suggestion}' for CLI parity"
+            )
+
+
+# ── api/config.py — reasoning helpers ────────────────────────────────────────
+
+class TestReasoningConfigHelpers:
+    """Validate that api/config.py exposes the CLI-parity helpers and that
+    they read/write the same keys the CLI uses."""
+
+    def test_parse_reasoning_effort_matches_cli_semantics(self):
+        from api.config import parse_reasoning_effort, VALID_REASONING_EFFORTS
+        # Empty → None
+        assert parse_reasoning_effort('') is None
+        assert parse_reasoning_effort(None) is None
+        # none → disabled
+        assert parse_reasoning_effort('none') == {'enabled': False}
+        # Each valid level → {enabled, effort}
+        for level in VALID_REASONING_EFFORTS:
+            assert parse_reasoning_effort(level) == {'enabled': True, 'effort': level}
+        # Unknown → None (fall back to default)
+        assert parse_reasoning_effort('garbage') is None
+        # Case-insensitive + trimmed
+        assert parse_reasoning_effort('  HIGH  ') == {'enabled': True, 'effort': 'high'}
+
+    def test_valid_reasoning_efforts_matches_hermes_constants(self):
+        """Ensure our mirror stays in sync with hermes_constants."""
+        from api.config import VALID_REASONING_EFFORTS
+        # Snapshot-style assertion: if hermes_constants adds a level, this
+        # test will fail fast so we know to update WebUI too.
+        assert VALID_REASONING_EFFORTS == (
+            'minimal', 'low', 'medium', 'high', 'xhigh'
+        )
+
+    def test_set_reasoning_effort_persists_to_config_yaml(self, tmp_path, monkeypatch):
+        """set_reasoning_effort writes agent.reasoning_effort to the active
+        profile's config.yaml — the same key the CLI writes."""
+        import api.config as cfg
+        cfgfile = tmp_path / 'config.yaml'
+        monkeypatch.setattr(cfg, '_get_config_path', lambda: cfgfile)
+        cfg.set_reasoning_effort('high')
+        import yaml as _yaml
+        data = _yaml.safe_load(cfgfile.read_text(encoding='utf-8'))
+        assert data.get('agent', {}).get('reasoning_effort') == 'high', (
+            "agent.reasoning_effort must be persisted to config.yaml"
+        )
+
+    def test_set_reasoning_display_persists_to_config_yaml(self, tmp_path, monkeypatch):
+        """set_reasoning_display writes display.show_reasoning to the same
+        config.yaml the CLI writes."""
+        import api.config as cfg
+        cfgfile = tmp_path / 'config.yaml'
+        monkeypatch.setattr(cfg, '_get_config_path', lambda: cfgfile)
+        cfg.set_reasoning_display(False)
+        import yaml as _yaml
+        data = _yaml.safe_load(cfgfile.read_text(encoding='utf-8'))
+        assert data.get('display', {}).get('show_reasoning') is False, (
+            "display.show_reasoning must be persisted to config.yaml"
+        )
+        cfg.set_reasoning_display(True)
+        data = _yaml.safe_load(cfgfile.read_text(encoding='utf-8'))
+        assert data.get('display', {}).get('show_reasoning') is True
+
+    def test_set_reasoning_effort_rejects_invalid(self, tmp_path, monkeypatch):
+        import api.config as cfg
+        monkeypatch.setattr(cfg, '_get_config_path', lambda: tmp_path / 'config.yaml')
+        import pytest as _pt
+        with _pt.raises(ValueError):
+            cfg.set_reasoning_effort('garbage')
+        with _pt.raises(ValueError):
+            cfg.set_reasoning_effort('')
+
+    def test_get_reasoning_status_defaults_to_show_true(self, tmp_path, monkeypatch):
+        """When config.yaml has no display section, show_reasoning defaults
+        to True (matches CLI default where the setting is opt-in)."""
+        import api.config as cfg
+        monkeypatch.setattr(cfg, '_get_config_path', lambda: tmp_path / 'config.yaml')
+        st = cfg.get_reasoning_status()
+        assert st['show_reasoning'] is True
+        assert st['reasoning_effort'] == ''
+
+
+# ── api/streaming.py — AIAgent receives reasoning_config ──────────────────────
+
+class TestStreamingReasoningWiring:
+    """Confirm api/streaming.py reads agent.reasoning_effort from config and
+    passes parsed reasoning_config to AIAgent (so effort changes take effect
+    on the next session)."""
+
+    def test_streaming_reads_reasoning_effort_from_config(self):
+        src = read('api/streaming.py')
+        assert 'parse_reasoning_effort' in src, (
+            "api/streaming.py must import parse_reasoning_effort to translate "
+            "config.yaml agent.reasoning_effort into AIAgent reasoning_config"
+        )
+        assert "reasoning_config" in src and "'reasoning_config' in _agent_params" in src, (
+            "api/streaming.py must guard the reasoning_config kwarg with "
+            "inspect.signature so older hermes-agent builds don't TypeError"
+        )
+
+
+# ── api/routes.py — /api/reasoning endpoints ──────────────────────────────────
+
+class TestReasoningRoutes:
+
+    def test_get_api_reasoning_route_exists(self):
+        src = read('api/routes.py')
+        assert 'parsed.path == "/api/reasoning"' in src, (
+            "GET /api/reasoning route must exist"
+        )
+        assert 'get_reasoning_status' in src, (
+            "api/routes.py must import and call get_reasoning_status"
+        )
+
+    def test_post_api_reasoning_accepts_display(self):
+        src = read('api/routes.py')
+        # The POST branch reads 'display' from body and dispatches to
+        # set_reasoning_display.
+        assert 'set_reasoning_display' in src, (
+            "POST /api/reasoning must route display toggles through "
+            "set_reasoning_display"
+        )
+
+    def test_post_api_reasoning_accepts_effort(self):
+        src = read('api/routes.py')
+        assert 'set_reasoning_effort' in src, (
+            "POST /api/reasoning must route effort changes through "
+            "set_reasoning_effort"
+        )