diff --git a/src/cli/App.tsx b/src/cli/App.tsx
index a9f3f7b..6602693 100644
--- a/src/cli/App.tsx
+++ b/src/cli/App.tsx
@@ -231,6 +231,7 @@ import {
   buildQueuedUserText,
   getQueuedNotificationSummaries,
 } from "./helpers/queuedMessageParts";
+import { resolveReasoningTabToggleCommand } from "./helpers/reasoningTabToggle";
 import { safeJsonParseOr } from "./helpers/safeJsonParse";
 import { getDeviceType, getLocalTime } from "./helpers/sessionContext";
 import {
@@ -479,6 +480,7 @@ const NON_STATE_COMMANDS = new Set([
   "/export",
   "/download",
   "/statusline",
+  "/reasoning-tab",
 ]);
 
 // Check if a command is interactive (opens overlay, should not be queued)
@@ -925,6 +927,7 @@ export default function App({
   messageHistory = [],
   resumedExistingConversation = false,
   tokenStreaming = false,
+  reasoningTabCycleEnabled: initialReasoningTabCycleEnabled = false,
   showCompactions = false,
   agentProvenance = null,
   releaseNotes = null,
@@ -945,6 +948,7 @@ export default function App({
   messageHistory?: Message[];
   resumedExistingConversation?: boolean; // True if we explicitly resumed via --resume
   tokenStreaming?: boolean;
+  reasoningTabCycleEnabled?: boolean;
   showCompactions?: boolean;
   agentProvenance?: AgentProvenance | null;
   releaseNotes?: string | null; // Markdown release notes to display above header
@@ -1484,6 +1488,11 @@ export default function App({
   const [tokenStreamingEnabled, setTokenStreamingEnabled] =
     useState(tokenStreaming);
 
+  // Reasoning tier Tab cycling preference (opt-in only, persisted globally)
+  const [reasoningTabCycleEnabled, setReasoningTabCycleEnabled] = useState(
+    initialReasoningTabCycleEnabled,
+  );
+
   // Show compaction messages preference (can be toggled at runtime)
   const [showCompactionsEnabled, _setShowCompactionsEnabled] =
     useState(showCompactions);
@@ -7348,6 +7357,52 @@ export default function App({
           return { submitted: true };
         }
 
+        // Special handling for /reasoning-tab command - opt-in toggle for Tab tier cycling
+        if (
+          trimmed === "/reasoning-tab" ||
+          trimmed.startsWith("/reasoning-tab ")
+        ) {
+          const resolution = resolveReasoningTabToggleCommand(
+            trimmed,
+            reasoningTabCycleEnabled,
+          );
+          if (!resolution) {
+            return { submitted: false };
+          }
+          const cmd = commandRunner.start(
+            trimmed,
+            "Updating reasoning Tab shortcut...",
+          );
+
+          setCommandRunning(true);
+
+          try {
+            if (resolution.kind === "status") {
+              cmd.finish(resolution.message, true);
+              return { submitted: true };
+            }
+
+            if (resolution.kind === "invalid") {
+              cmd.fail(resolution.message);
+              return { submitted: true };
+            }
+
+            setReasoningTabCycleEnabled(resolution.enabled);
+            settingsManager.updateSettings({
+              reasoningTabCycleEnabled: resolution.enabled,
+            });
+
+            cmd.finish(resolution.message, true);
+          } catch (error) {
+            const errorDetails = formatErrorDetails(error, agentId);
+            cmd.fail(`Failed: ${errorDetails}`);
+          } finally {
+            setCommandRunning(false);
+          }
+
+          return { submitted: true };
+        }
+
         // Special handling for /new command - start new conversation
         if (msg.trim() === "/new") {
           const cmd = commandRunner.start(
@@ -12406,7 +12461,11 @@ Plan file path: ${planFilePath}`;
                 }
                 permissionMode={uiPermissionMode}
                 onPermissionModeChange={handlePermissionModeChange}
-                onCycleReasoningEffort={handleCycleReasoningEffort}
+                onCycleReasoningEffort={
+                  reasoningTabCycleEnabled
+                    ? handleCycleReasoningEffort
+                    : undefined
+                }
                 onExit={handleExit}
                 onInterrupt={handleInterrupt}
                 interruptRequested={interruptRequested}
diff --git a/src/cli/commands/registry.ts b/src/cli/commands/registry.ts
index 0f2c98f..75ee943 100644
--- a/src/cli/commands/registry.ts
+++ b/src/cli/commands/registry.ts
@@ -288,6 +288,15 @@ export const commands: Record<string, Command> = {
       return "Managing status line...";
     },
   },
+  "/reasoning-tab": {
+    desc: "Toggle Tab shortcut for reasoning tiers (/reasoning-tab on|off|status)",
+    args: "[on|off|status]",
+    order: 36.6,
+    handler: () => {
+      // Handled specially in App.tsx
+      return "Managing reasoning Tab shortcut...";
+    },
+  },
   "/terminal": {
     desc: "Setup terminal shortcuts [--revert]",
     order: 37,
diff --git a/src/cli/helpers/reasoningTabToggle.ts b/src/cli/helpers/reasoningTabToggle.ts
new file mode 100644
index 0000000..b9f79b1
--- /dev/null
+++ b/src/cli/helpers/reasoningTabToggle.ts
@@ -0,0 +1,47 @@
+export type ReasoningTabToggleResolution =
+  | { kind: "status"; message: string }
+  | { kind: "set"; enabled: boolean; message: string }
+  | { kind: "invalid"; message: string };
+
+const ENABLE_ARGS = new Set(["on", "enable", "enabled", "true", "1"]);
+const DISABLE_ARGS = new Set(["off", "disable", "disabled", "false", "0"]);
+
+const USAGE = "Usage: /reasoning-tab [on|off|status] (default is off)";
+
+export function resolveReasoningTabToggleCommand(
+  trimmedInput: string,
+  currentlyEnabled: boolean,
+): ReasoningTabToggleResolution | null {
+  const trimmed = trimmedInput.trim();
+  if (trimmed !== "/reasoning-tab" && !trimmed.startsWith("/reasoning-tab ")) {
+    return null;
+  }
+
+  const rawArg = trimmed.slice("/reasoning-tab".length).trim().toLowerCase();
+  if (!rawArg || rawArg === "status") {
+    return {
+      kind: "status",
+      message: currentlyEnabled
+        ? "Reasoning Tab shortcut is enabled. Tab now cycles reasoning tiers."
+        : "Reasoning Tab shortcut is disabled. Use /reasoning-tab on to enable it.",
+    };
+  }
+
+  if (ENABLE_ARGS.has(rawArg)) {
+    return {
+      kind: "set",
+      enabled: true,
+      message: "Reasoning Tab shortcut enabled.",
+    };
+  }
+
+  if (DISABLE_ARGS.has(rawArg)) {
+    return {
+      kind: "set",
+      enabled: false,
+      message: "Reasoning Tab shortcut disabled.",
+    };
+  }
+
+  return { kind: "invalid", message: USAGE };
+}
diff --git a/src/index.ts b/src/index.ts
index e2b7f10..a8a0d7a 100755
--- a/src/index.ts
+++ b/src/index.ts
@@ -2044,6 +2044,7 @@ async function main(): Promise<void> {
         messageHistory: resumeData?.messageHistory ?? EMPTY_MESSAGE_ARRAY,
         resumedExistingConversation,
         tokenStreaming: settings.tokenStreaming,
+        reasoningTabCycleEnabled: settings.reasoningTabCycleEnabled === true,
         showCompactions: settings.showCompactions,
         agentProvenance,
         releaseNotes,
@@ -2062,6 +2063,7 @@ async function main(): Promise<void> {
       messageHistory: resumeData?.messageHistory ?? EMPTY_MESSAGE_ARRAY,
       resumedExistingConversation,
       tokenStreaming: settings.tokenStreaming,
+      reasoningTabCycleEnabled: settings.reasoningTabCycleEnabled === true,
       showCompactions: settings.showCompactions,
       agentProvenance,
       releaseNotes,
diff --git a/src/settings-manager.ts b/src/settings-manager.ts
index c91dcf9..a2338b6 100644
--- a/src/settings-manager.ts
+++ b/src/settings-manager.ts
@@ -62,6 +62,7 @@ export interface Settings {
   lastAgent: string | null; // DEPRECATED: kept for migration to lastSession
   lastSession?: SessionRef; // DEPRECATED: kept for backwards compat, use sessionsByServer
   tokenStreaming: boolean;
+  reasoningTabCycleEnabled: boolean; // Tab cycles reasoning tiers only when explicitly enabled
   showCompactions?: boolean;
   enableSleeptime: boolean;
   sessionContextEnabled: boolean; // Send device/agent context on first message of each session
@@ -126,6 +127,7 @@ export interface LocalProjectSettings {
 const DEFAULT_SETTINGS: Settings = {
   lastAgent: null,
   tokenStreaming: false,
+  reasoningTabCycleEnabled: false,
   showCompactions: false,
   enableSleeptime: false,
   conversationSwitchAlertEnabled: false,
diff --git a/src/tests/cli/reasoning-cycle-wiring.test.ts b/src/tests/cli/reasoning-cycle-wiring.test.ts
index eb49628..fbef40d 100644
--- a/src/tests/cli/reasoning-cycle-wiring.test.ts
+++ b/src/tests/cli/reasoning-cycle-wiring.test.ts
@@ -45,4 +45,30 @@ describe("reasoning tier cycle wiring", () => {
 
     expect(callbackBlocks.length).toBeGreaterThanOrEqual(2);
   });
+
+  test("tab-based reasoning cycling is opt-in only", () => {
+    const appPath = fileURLToPath(
+      new URL("../../cli/App.tsx", import.meta.url),
+    );
+    const indexPath = fileURLToPath(new URL("../../index.ts", import.meta.url));
+    const settingsPath = fileURLToPath(
+      new URL("../../settings-manager.ts", import.meta.url),
+    );
+
+    const appSource = readFileSync(appPath, "utf-8");
+    const indexSource = readFileSync(indexPath, "utf-8");
+    const settingsSource = readFileSync(settingsPath, "utf-8");
+
+    expect(settingsSource).toContain("reasoningTabCycleEnabled: boolean;");
+    expect(settingsSource).toContain("reasoningTabCycleEnabled: false,");
+    expect(indexSource).toContain(
+      "reasoningTabCycleEnabled: settings.reasoningTabCycleEnabled === true,",
+    );
+    expect(appSource).toMatch(
+      /if\s*\(\s*trimmed\s*===\s*"\/reasoning-tab"\s*\|\|\s*trimmed\.startsWith\("\/reasoning-tab "\)\s*\)\s*\{/,
+    );
+    expect(appSource).toMatch(
+      /onCycleReasoningEffort=\{\s*reasoningTabCycleEnabled\s*\?\s*handleCycleReasoningEffort\s*:\s*undefined\s*\}/,
+    );
+  });
 });
diff --git a/src/tests/cli/reasoning-tab-toggle.test.ts b/src/tests/cli/reasoning-tab-toggle.test.ts
new file mode 100644
index 0000000..5a22d35
--- /dev/null
+++ b/src/tests/cli/reasoning-tab-toggle.test.ts
@@ -0,0 +1,57 @@
+import { describe, expect, test } from "bun:test";
+import { resolveReasoningTabToggleCommand } from "../../cli/helpers/reasoningTabToggle";
+
+describe("reasoning tab toggle command parsing", () => {
+  test("returns null for non-matching commands", () => {
+    expect(resolveReasoningTabToggleCommand("/model", false)).toBeNull();
+  });
+
+  test("status/default reports current state", () => {
+    expect(resolveReasoningTabToggleCommand("/reasoning-tab", false)).toEqual({
+      kind: "status",
+      message:
+        "Reasoning Tab shortcut is disabled. Use /reasoning-tab on to enable it.",
+    });
+
+    expect(
+      resolveReasoningTabToggleCommand("/reasoning-tab status", true),
+    ).toEqual({
+      kind: "status",
+      message:
+        "Reasoning Tab shortcut is enabled. Tab now cycles reasoning tiers.",
+    });
+  });
+
+  test("accepts enable aliases", () => {
+    for (const arg of ["on", "enable", "enabled", "true", "1"]) {
+      expect(
+        resolveReasoningTabToggleCommand(`/reasoning-tab ${arg}`, false),
+      ).toEqual({
+        kind: "set",
+        enabled: true,
+        message: "Reasoning Tab shortcut enabled.",
+      });
+    }
+  });
+
+  test("accepts disable aliases", () => {
+    for (const arg of ["off", "disable", "disabled", "false", "0"]) {
+      expect(
+        resolveReasoningTabToggleCommand(`/reasoning-tab ${arg}`, true),
+      ).toEqual({
+        kind: "set",
+        enabled: false,
+        message: "Reasoning Tab shortcut disabled.",
+      });
+    }
+  });
+
+  test("returns usage for invalid arg", () => {
+    expect(
+      resolveReasoningTabToggleCommand("/reasoning-tab maybe", true),
+    ).toEqual({
+      kind: "invalid",
+      message: "Usage: /reasoning-tab [on|off|status] (default is off)",
+    });
+  });
+});