diff --git a/ui/desktop/index.html b/ui/desktop/index.html
index 78a85db070c2..6547abc5d63f 100644
--- a/ui/desktop/index.html
+++ b/ui/desktop/index.html
@@ -13,13 +13,18 @@
               const useSystemTheme = localStorage.getItem('use_system_theme') === 'true';
               const systemPrefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
               const savedTheme = localStorage.getItem('theme');
-              const isDark = useSystemTheme ? systemPrefersDark : (savedTheme ? savedTheme === 'dark' : systemPrefersDark);
+              const isGlass = !useSystemTheme && savedTheme === 'glass';
+              const isDark = useSystemTheme ? systemPrefersDark : (savedTheme ? savedTheme === 'dark' || savedTheme === 'glass' : systemPrefersDark);
               
-              if (isDark) {
+              if (isGlass) {
+                document.documentElement.classList.add('dark', 'glass');
+                document.documentElement.style.colorScheme = 'dark';
+              } else if (isDark) {
                 document.documentElement.classList.add('dark');
+                document.documentElement.classList.remove('glass');
                 document.documentElement.style.colorScheme = 'dark';
               } else {
-                document.documentElement.classList.remove('dark');
+                document.documentElement.classList.remove('dark', 'glass');
                 document.documentElement.style.colorScheme = 'light';
               }
             } else {
diff --git a/ui/desktop/src/components/GooseSidebar/ThemeSelector.tsx b/ui/desktop/src/components/GooseSidebar/ThemeSelector.tsx
index f3783bd753e9..6a1770432a17 100644
--- a/ui/desktop/src/components/GooseSidebar/ThemeSelector.tsx
+++ b/ui/desktop/src/components/GooseSidebar/ThemeSelector.tsx
@@ -1,5 +1,5 @@
 import React from 'react';
-import { Moon, Sliders, Sun } from 'lucide-react';
+import { Layers, Moon, Sliders, Sun } from 'lucide-react';
 import { Button } from '../ui/button';
 import { useTheme } from '../../contexts/ThemeContext';
 
@@ -20,7 +20,7 @@ const ThemeSelector: React.FC<ThemeSelectorProps> = ({
     <div className={`${!horizontal ? 'px-1 py-2 space-y-2' : ''} ${className}`}>
       {!hideTitle && <div className="text-xs text-text-primary px-3">Theme</div>}
       <div
-        className={`${horizontal ? 'flex' : 'grid grid-cols-3'} gap-1 ${!horizontal ? 'px-3' : ''}`}
+        className={`${horizontal ? 'flex' : 'grid grid-cols-4'} gap-1 ${!horizontal ? 'px-3' : ''}`}
       >
         <Button
           data-testid="light-mode-button"
@@ -52,6 +52,22 @@ const ThemeSelector: React.FC<ThemeSelectorProps> = ({
           <span>Dark</span>
         </Button>
 
+
+        <Button
+          data-testid="glass-mode-button"
+          onClick={() => setUserThemePreference('glass')}
+          className={`flex items-center justify-center gap-1 p-2 rounded-md border transition-colors text-xs ${
+            userThemePreference === 'glass'
+              ? 'bg-background-inverse text-text-inverse border-text-inverse hover:!bg-background-inverse hover:!text-text-inverse'
+              : 'border-border-primary hover:!bg-background-secondary text-text-secondary hover:text-text-primary'
+          }`}
+          variant="ghost"
+          size="sm"
+        >
+          <Layers className="h-3 w-3" />
+          <span>Glass</span>
+        </Button>
+
         <Button
           data-testid="system-mode-button"
           onClick={() => setUserThemePreference('system')}
diff --git a/ui/desktop/src/contexts/ThemeContext.tsx b/ui/desktop/src/contexts/ThemeContext.tsx
index 16c97e7bda68..72141bf196f8 100644
--- a/ui/desktop/src/contexts/ThemeContext.tsx
+++ b/ui/desktop/src/contexts/ThemeContext.tsx
@@ -2,8 +2,8 @@ import React, { createContext, useContext, useEffect, useState, useCallback } fr
 import { applyThemeTokens, buildMcpHostStyles } from '../theme/theme-tokens';
 import type { McpUiHostStyles } from '@modelcontextprotocol/ext-apps/app-bridge';
 
-type ThemePreference = 'light' | 'dark' | 'system';
-type ResolvedTheme = 'light' | 'dark';
+type ThemePreference = 'light' | 'dark' | 'glass' | 'system';
+type ResolvedTheme = 'light' | 'dark' | 'glass';
 
 interface ThemeContextValue {
   userThemePreference: ThemePreference;
@@ -25,11 +25,19 @@ function resolveTheme(preference: ThemePreference): ResolvedTheme {
   return preference;
 }
 
+function getThemeClass(theme: ResolvedTheme): string {
+  // Glass uses dark-mode text/UI conventions
+  return theme === 'glass' ? 'dark' : theme;
+}
+
 function applyThemeToDocument(theme: ResolvedTheme): void {
-  const toRemove = theme === 'dark' ? 'light' : 'dark';
-  document.documentElement.classList.add(theme);
+  const themeClass = getThemeClass(theme);
+  const toRemove = themeClass === 'dark' ? 'light' : 'dark';
+  document.documentElement.classList.add(themeClass);
   document.documentElement.classList.remove(toRemove);
-  document.documentElement.style.colorScheme = theme;
+  // Toggle glass class for backdrop-filter styles
+  document.documentElement.classList.toggle('glass', theme === 'glass');
+  document.documentElement.style.colorScheme = themeClass;
 }
 
 // Built once — light-dark() values are theme-independent
@@ -55,8 +63,10 @@ export function ThemeProvider({ children }: ThemeProviderProps) {
         let preference: ThemePreference;
         if (useSystemTheme) {
           preference = 'system';
-        } else {
+        } else if (savedTheme === 'glass' || savedTheme === 'dark' || savedTheme === 'light') {
           preference = savedTheme;
+        } else {
+          preference = 'light';
         }
 
         setUserThemePreferenceState(preference);
@@ -117,9 +127,11 @@ export function ThemeProvider({ children }: ThemeProviderProps) {
       const themeData = args[0] as { useSystemTheme: boolean; theme: string };
       const newPreference: ThemePreference = themeData.useSystemTheme
         ? 'system'
-        : themeData.theme === 'dark'
-          ? 'dark'
-          : 'light';
+        : themeData.theme === 'glass'
+          ? 'glass'
+          : themeData.theme === 'dark'
+            ? 'dark'
+            : 'light';
 
       setUserThemePreferenceState(newPreference);
       setResolvedTheme(resolveTheme(newPreference));
diff --git a/ui/desktop/src/styles/main.css b/ui/desktop/src/styles/main.css
index f4f96837f9df..d29e1de2efdb 100644
--- a/ui/desktop/src/styles/main.css
+++ b/ui/desktop/src/styles/main.css
@@ -927,3 +927,58 @@ p > code.bg-inline-code {
 .mcp-app-container.mcp-enter-inline {
   animation: mcp-enter-inline 180ms cubic-bezier(0.2, 0, 0, 1) both;
 }
+
+/* ═══════════════════════════════════════════════════════════════════════════
+   GLASS THEME — backdrop-filter for native vibrancy blur-through
+   Applied when html.glass is set by ThemeContext.
+   On macOS, Electron's vibrancy: 'window' provides the native blur layer;
+   these styles make the CSS backgrounds transparent enough to reveal it.
+   On other platforms, backdrop-filter provides a CSS-only approximation.
+   ═══════════════════════════════════════════════════════════════════════════ */
+
+html.glass body {
+  background-color: transparent;
+}
+
+html.glass #root {
+  backdrop-filter: blur(20px) saturate(180%);
+  -webkit-backdrop-filter: blur(20px) saturate(180%);
+}
+
+.glass {
+  /* Legacy aliases */
+  --text-inverse: var(--color-black);
+  --text-danger: var(--color-red-100);
+
+  /* Search highlighting */
+  --highlight-color: rgba(255, 213, 0, 0.4);
+  --highlight-current: rgba(252, 213, 3, 0.5);
+
+  /* Sidebar aliases — semi-transparent for glass effect */
+  --sidebar: var(--color-background-secondary);
+  --sidebar-foreground: var(--color-text-primary);
+  --sidebar-primary: var(--color-background-inverse);
+  --sidebar-primary-foreground: var(--color-text-inverse);
+  --sidebar-accent: var(--color-background-secondary);
+  --sidebar-accent-foreground: var(--color-text-primary);
+  --sidebar-border: var(--color-border-primary);
+  --sidebar-ring: var(--color-border-primary);
+
+  /* Custom shadow — softer for glass */
+  --shadow-default:
+    0px 12px 32px 0px rgba(0, 0, 0, 0.15), 0px 8px 16px 0px rgba(0, 0, 0, 0.1),
+    0px 2px 4px 0px rgba(0, 0, 0, 0.08), 0px 0px 1px 0px rgba(255, 255, 255, 0.1);
+}
+
+/* Glass scrollbar — more transparent */
+.glass * {
+  scrollbar-color: rgba(255, 255, 255, 0.15) transparent;
+}
+
+.glass ::-webkit-scrollbar-thumb {
+  background-color: rgba(255, 255, 255, 0.15);
+}
+
+.glass ::-webkit-scrollbar-thumb:hover {
+  background-color: rgba(255, 255, 255, 0.25);
+}
diff --git a/ui/desktop/src/theme/theme-tokens.ts b/ui/desktop/src/theme/theme-tokens.ts
index fa1d2d5d622a..4f7d9a46177f 100644
--- a/ui/desktop/src/theme/theme-tokens.ts
+++ b/ui/desktop/src/theme/theme-tokens.ts
@@ -200,11 +200,69 @@ const darkColorTokens: ColorTokens = {
   '--shadow-lg': '0 10px 15px -3px rgba(0, 0, 0, 0.3), 0 4px 6px -4px rgba(0, 0, 0, 0.2)',
 };
 
+
+// ---------------------------------------------------------------------------
+// Glass theme — semi-transparent colors for native vibrancy blur-through
+// ---------------------------------------------------------------------------
+const glassColorTokens: ColorTokens = {
+  // Backgrounds — semi-transparent to let native vibrancy show through
+  '--color-background-primary': 'rgba(30, 30, 30, 0.55)',
+  '--color-background-secondary': 'rgba(50, 50, 50, 0.45)',
+  '--color-background-tertiary': 'rgba(70, 70, 70, 0.35)',
+  '--color-background-inverse': 'rgba(205, 209, 214, 0.9)',
+  '--color-background-ghost': 'transparent',
+  '--color-background-info': '#7cacff',
+  '--color-background-danger': '#ff6b6b',
+  '--color-background-success': '#a3d795',
+  '--color-background-warning': '#ffd966',
+  '--color-background-disabled': 'rgba(71, 78, 87, 0.4)',
+
+  // Text — fully opaque for readability against translucent backgrounds
+  '--color-text-primary': '#ffffff',
+  '--color-text-secondary': '#a0a0a0',
+  '--color-text-tertiary': '#707a86',
+  '--color-text-inverse': '#000000',
+  '--color-text-ghost': '#a0a0a0',
+  '--color-text-info': '#7cacff',
+  '--color-text-danger': '#ff6b6b',
+  '--color-text-success': '#a3d795',
+  '--color-text-warning': '#ffd966',
+  '--color-text-disabled': '#525b68',
+
+  // Borders — subtle, semi-transparent
+  '--color-border-primary': 'rgba(255, 255, 255, 0.1)',
+  '--color-border-secondary': 'rgba(255, 255, 255, 0.15)',
+  '--color-border-tertiary': 'rgba(255, 255, 255, 0.08)',
+  '--color-border-inverse': '#ffffff',
+  '--color-border-ghost': 'transparent',
+  '--color-border-info': '#7cacff',
+  '--color-border-danger': '#ff6b6b',
+  '--color-border-success': '#a3d795',
+  '--color-border-warning': '#ffd966',
+  '--color-border-disabled': 'rgba(255, 255, 255, 0.05)',
+
+  // Rings — semi-transparent
+  '--color-ring-primary': 'rgba(255, 255, 255, 0.15)',
+  '--color-ring-secondary': 'rgba(255, 255, 255, 0.1)',
+  '--color-ring-inverse': '#000000',
+  '--color-ring-info': '#7cacff',
+  '--color-ring-danger': '#ff6b6b',
+  '--color-ring-success': '#a3d795',
+  '--color-ring-warning': '#ffd966',
+
+  // Shadows — softer, with slight glow
+  '--shadow-hairline': '0 0 0 1px rgba(255, 255, 255, 0.05)',
+  '--shadow-sm': '0 1px 2px 0 rgba(0, 0, 0, 0.15)',
+  '--shadow-md': '0 4px 6px -1px rgba(0, 0, 0, 0.2), 0 2px 4px -2px rgba(0, 0, 0, 0.15)',
+  '--shadow-lg': '0 10px 15px -3px rgba(0, 0, 0, 0.25), 0 4px 6px -4px rgba(0, 0, 0, 0.15)',
+};
+
 // ---------------------------------------------------------------------------
 // Merged token maps — used by applyThemeTokens() and buildMcpHostStyles()
 // ---------------------------------------------------------------------------
 export const lightTokens: ThemeTokens = { ...baseTokens, ...lightColorTokens };
 export const darkTokens: ThemeTokens = { ...baseTokens, ...darkColorTokens };
+export const glassTokens: ThemeTokens = { ...baseTokens, ...glassColorTokens };
 
 // ---------------------------------------------------------------------------
 // Helpers
@@ -266,21 +324,23 @@ export function buildMcpHostStyles(): McpUiHostStyles {
 /**
  * Resolve the current theme from localStorage / system preference.
  */
-export function getResolvedTheme(): 'light' | 'dark' {
+export function getResolvedTheme(): 'light' | 'dark' | 'glass' {
   const useSystem = localStorage.getItem('use_system_theme') !== 'false';
   if (useSystem) {
     return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
   }
-  return localStorage.getItem('theme') === 'dark' ? 'dark' : 'light';
+  const saved = localStorage.getItem('theme');
+  if (saved === 'glass') return 'glass';
+  return saved === 'dark' ? 'dark' : 'light';
 }
 
 /**
  * Apply theme tokens to the document root as CSS custom properties.
  * When called without an argument, resolves the theme from localStorage.
  */
-export function applyThemeTokens(theme?: 'light' | 'dark'): void {
+export function applyThemeTokens(theme?: 'light' | 'dark' | 'glass'): void {
   const resolved = theme ?? getResolvedTheme();
-  const tokens = resolved === 'dark' ? darkTokens : lightTokens;
+  const tokens = resolved === 'glass' ? glassTokens : resolved === 'dark' ? darkTokens : lightTokens;
   const root = document.documentElement;
   for (const [key, value] of Object.entries(tokens)) {
     root.style.setProperty(key, value);