diff --git a/frontend/src/components/layout/SidebarNav.vue b/frontend/src/components/layout/SidebarNav.vue
index 9a580838a..8de2d8341 100644
--- a/frontend/src/components/layout/SidebarNav.vue
+++ b/frontend/src/components/layout/SidebarNav.vue
@@ -1,64 +1,98 @@
 <template>
-  <nav class="sidebar-nav w-full px-3">
-    <div
-      v-for="(group, index) in items"
-      :key="index"
-      class="space-y-1 mb-5"
+  <TooltipProvider :delay-duration="150">
+    <nav
+      class="sidebar-nav w-full"
+      :class="collapsed ? 'px-2' : 'px-3'"
+      :data-collapsed="collapsed"
     >
-      <!-- Section Header -->
       <div
-        v-if="group.title"
-        class="px-2.5 pb-1 flex items-center gap-2"
-        :class="index > 0 ? 'pt-1' : ''"
+        v-for="(group, index) in items"
+        :key="index"
+        :class="[
+          collapsed ? 'mb-1 space-y-0' : 'mb-5 space-y-1',
+          collapsed && index > 0 ? 'border-t border-[#3d3929]/10 pt-1 dark:border-white/10' : ''
+        ]"
+        :data-sidebar-group-divider="collapsed && index > 0 ? '' : undefined"
       >
-        <span class="text-[10px] font-medium text-muted-foreground/50 font-mono tabular-nums">{{ String(index + 1).padStart(2, '0') }}</span>
-        <span class="text-[10px] font-semibold text-muted-foreground/70 uppercase tracking-[0.1em]">{{ group.title }}</span>
-      </div>
-
-      <!-- Links -->
-      <div class="space-y-0.5">
-        <template
-          v-for="item in group.items"
-          :key="item.href"
+        <!-- Section Header -->
+        <div
+          v-if="group.title && !collapsed"
+          class="flex items-center gap-2 px-2.5 pb-1"
+          :class="index > 0 ? 'pt-1' : ''"
         >
-          <RouterLink
-            :to="item.href"
-            class="group relative flex items-center justify-between px-2.5 py-2 rounded-lg transition-all duration-200"
-            :class="[
-              isItemActive(item.href)
-                ? 'bg-primary/10 text-primary font-medium'
-                : 'text-muted-foreground hover:text-foreground hover:bg-muted/50'
-            ]"
-            @pointerenter="schedulePrefetch(item.href)"
-            @pointerleave="cancelScheduledPrefetch(item.href)"
-            @pointerdown="prefetchNow(item.href)"
-            @focus="prefetchNow(item.href)"
-            @click="handleNavigate(item.href)"
-          >
-            <div class="flex items-center gap-2.5">
-              <component
-                :is="item.icon"
-                class="h-4 w-4 transition-colors duration-200"
-                :class="isItemActive(item.href) ? 'text-primary' : 'text-muted-foreground/70 group-hover:text-foreground'"
-                :stroke-width="isItemActive(item.href) ? 2 : 1.75"
-              />
-              <span class="text-[13px] tracking-tight">{{ item.name }}</span>
-            </div>
+          <span class="text-[10px] font-medium text-muted-foreground/50 font-mono tabular-nums">{{ String(index + 1).padStart(2, '0') }}</span>
+          <span class="text-[10px] font-semibold text-muted-foreground/70 uppercase tracking-[0.1em]">{{ group.title }}</span>
+        </div>
 
-            <!-- Active Indicator -->
-            <div
-              v-if="isItemActive(item.href)"
-              class="w-1 h-1 rounded-full bg-primary"
-            />
-          </RouterLink>
-        </template>
+        <!-- Links -->
+        <div class="space-y-0.5">
+          <template
+            v-for="item in group.items"
+            :key="item.href"
+          >
+            <Tooltip
+              :open="collapsed && openTooltipHref === item.href"
+              @update:open="handleTooltipOpenChange(item.href, $event)"
+            >
+              <TooltipTrigger as-child>
+                <RouterLink
+                  :to="item.href"
+                  class="group relative flex items-center rounded-lg"
+                  :class="[
+                    collapsed
+                      ? 'h-9 justify-center px-0 transition-colors duration-150'
+                      : 'justify-between px-2.5 py-2 transition-all duration-200',
+                    isItemActive(item.href)
+                      ? 'bg-primary/10 text-primary font-medium'
+                      : 'text-muted-foreground hover:text-foreground hover:bg-muted/50'
+                  ]"
+                  :aria-label="collapsed ? item.name : undefined"
+                  @pointerenter="schedulePrefetch(item.href)"
+                  @pointerleave="cancelScheduledPrefetch(item.href)"
+                  @pointerdown="prefetchNow(item.href)"
+                  @focus="prefetchNow(item.href)"
+                  @click="handleNavigate(item.href)"
+                >
+                  <div class="flex min-w-0 items-center gap-2.5">
+                    <component
+                      :is="item.icon"
+                      class="h-4 w-4 shrink-0 transition-colors duration-200"
+                      :class="isItemActive(item.href) ? 'text-primary' : 'text-muted-foreground/70 group-hover:text-foreground'"
+                      :stroke-width="isItemActive(item.href) ? 2 : 1.75"
+                    />
+                    <span
+                      v-if="!collapsed"
+                      class="truncate text-[13px] tracking-tight"
+                    >{{ item.name }}</span>
+                  </div>
+
+                  <!-- Active Indicator -->
+                  <div
+                    v-if="isItemActive(item.href)"
+                    class="h-1 w-1 shrink-0 rounded-full bg-primary"
+                    :class="collapsed ? 'absolute right-1.5' : ''"
+                  />
+                </RouterLink>
+              </TooltipTrigger>
+              <TooltipContent
+                v-if="collapsed"
+                side="right"
+                :side-offset="10"
+                class="text-xs"
+              >
+                {{ item.name }}
+              </TooltipContent>
+            </Tooltip>
+          </template>
+        </div>
       </div>
-    </div>
-  </nav>
+    </nav>
+  </TooltipProvider>
 </template>
 
 <script setup lang="ts">
-import { onBeforeUnmount, type Component } from 'vue'
+import { onBeforeUnmount, ref, type Component } from 'vue'
+import { Tooltip, TooltipContent, TooltipProvider, TooltipTrigger } from '@/components/ui/tooltip'
 
 export interface NavigationItem {
   name: string
@@ -76,6 +110,7 @@ const props = defineProps<{
   items: NavigationGroup[]
   activePath?: string
   isActive?: (href: string) => boolean
+  collapsed?: boolean
 }>()
 
 const emit = defineEmits<{
@@ -86,6 +121,19 @@ const emit = defineEmits<{
 const HOVER_PREFETCH_DELAY_MS = 100
 let scheduledPrefetchHref: string | null = null
 let scheduledPrefetchTimer: ReturnType<typeof setTimeout> | null = null
+const openTooltipHref = ref<string | null>(null)
+
+function handleTooltipOpenChange(href: string, open: boolean) {
+  if (!props.collapsed) {
+    openTooltipHref.value = null
+    return
+  }
+  if (open) {
+    openTooltipHref.value = href
+  } else if (openTooltipHref.value === href) {
+    openTooltipHref.value = null
+  }
+}
 
 function cancelScheduledPrefetch(href?: string) {
   if (href && scheduledPrefetchHref !== href) return
diff --git a/frontend/src/components/layout/__tests__/SidebarNav.spec.ts b/frontend/src/components/layout/__tests__/SidebarNav.spec.ts
new file mode 100644
index 000000000..e7412d1d4
--- /dev/null
+++ b/frontend/src/components/layout/__tests__/SidebarNav.spec.ts
@@ -0,0 +1,87 @@
+import { afterEach, describe, expect, it } from 'vitest'
+import { createApp, defineComponent, h, nextTick, ref, type App } from 'vue'
+
+import SidebarNav from '@/components/layout/SidebarNav.vue'
+
+const mountedApps: Array<{ app: App, root: HTMLElement }> = []
+
+const TestIcon = defineComponent({
+  name: 'TestIcon',
+  setup: () => () => h('svg', { 'data-testid': 'nav-icon' }),
+})
+
+const RouterLinkStub = defineComponent({
+  name: 'RouterLink',
+  inheritAttrs: false,
+  props: {
+    to: {
+      type: String,
+      required: true,
+    },
+  },
+  setup(props, { attrs, slots }) {
+    return () => h('a', { ...attrs, href: props.to }, slots.default?.())
+  },
+})
+
+afterEach(() => {
+  for (const { app, root } of mountedApps.splice(0)) {
+    app.unmount()
+    root.remove()
+  }
+})
+
+describe('SidebarNav', () => {
+  it('switches from labelled navigation to accessible icon-only links', async () => {
+    const collapsed = ref(false)
+    const root = document.createElement('div')
+    document.body.appendChild(root)
+
+    const app = createApp({
+      setup: () => () => h(SidebarNav, {
+        items: [{
+          title: 'Overview',
+          items: [
+            { name: 'Dashboard', href: '/dashboard', icon: TestIcon },
+            { name: 'Usage', href: '/usage', icon: TestIcon },
+          ],
+        }, {
+          title: 'Management',
+          items: [
+            { name: 'Settings', href: '/settings', icon: TestIcon },
+          ],
+        }],
+        activePath: '/dashboard',
+        collapsed: collapsed.value,
+      }),
+    })
+    app.component('RouterLink', RouterLinkStub)
+    app.mount(root)
+    mountedApps.push({ app, root })
+
+    expect(root.querySelector('nav')?.dataset.collapsed).toBe('false')
+    expect(root.textContent).toContain('Overview')
+    expect(root.textContent).toContain('Management')
+    expect(root.textContent).toContain('Dashboard')
+    expect(root.querySelectorAll('[data-sidebar-group-divider]')).toHaveLength(0)
+    const expandedDashboardLink = root.querySelector('a[href="/dashboard"]')
+    expect(expandedDashboardLink?.hasAttribute('aria-label')).toBe(false)
+    expect(expandedDashboardLink?.classList.contains('py-2')).toBe(true)
+    expect(expandedDashboardLink?.classList.contains('h-9')).toBe(false)
+
+    collapsed.value = true
+    await nextTick()
+
+    expect(root.querySelector('nav')?.dataset.collapsed).toBe('true')
+    expect(root.textContent).not.toContain('Overview')
+    expect(root.textContent).not.toContain('Management')
+    expect(root.textContent).not.toContain('Dashboard')
+    expect(root.querySelectorAll('[data-testid="nav-icon"]')).toHaveLength(3)
+    expect(root.querySelectorAll('[data-sidebar-group-divider]')).toHaveLength(1)
+    const collapsedDashboardLink = root.querySelector('a[href="/dashboard"]')
+    expect(collapsedDashboardLink?.getAttribute('aria-label')).toBe('Dashboard')
+    expect(collapsedDashboardLink?.classList.contains('h-9')).toBe(true)
+    expect(collapsedDashboardLink?.classList.contains('py-2')).toBe(false)
+    expect(root.querySelector('a[href="/usage"]')?.getAttribute('aria-label')).toBe('Usage')
+  })
+})
diff --git a/frontend/src/i18n/messages.ts b/frontend/src/i18n/messages.ts
index a5ce83067..edfa58823 100644
--- a/frontend/src/i18n/messages.ts
+++ b/frontend/src/i18n/messages.ts
@@ -269,6 +269,8 @@ export const messages = {
     'nav.group.account': '账户',
     'nav.group.management': '管理',
     'nav.group.system': '系统',
+    'nav.collapseSidebar': '收起侧边栏',
+    'nav.expandSidebar': '展开侧边栏',
     'nav.dashboard': '仪表盘',
     'nav.healthMonitor': '健康监控',
     'nav.modelCatalog': '模型目录',
@@ -580,6 +582,8 @@ export const messages = {
     'nav.group.account': 'Account',
     'nav.group.management': 'Management',
     'nav.group.system': 'System',
+    'nav.collapseSidebar': 'Collapse sidebar',
+    'nav.expandSidebar': 'Expand sidebar',
     'nav.dashboard': 'Dashboard',
     'nav.healthMonitor': 'Health monitor',
     'nav.modelCatalog': 'Model catalog',
diff --git a/frontend/src/layouts/MainLayout.vue b/frontend/src/layouts/MainLayout.vue
index a7ba67885..a87c9f799 100644
--- a/frontend/src/layouts/MainLayout.vue
+++ b/frontend/src/layouts/MainLayout.vue
@@ -23,64 +23,155 @@
     </template>
 
     <template #sidebar>
-      <!-- HEADER (Brand) -->
-      <div class="shrink-0 flex items-center px-6 h-20">
-        <RouterLink
-          to="/"
-          class="flex items-center gap-3 group transition-opacity hover:opacity-80"
+      <div class="flex h-full w-full min-w-0 flex-col overflow-hidden">
+        <!-- HEADER (Brand) -->
+        <div
+          class="group/sidebar-brand relative flex shrink-0 items-center transition-[height,padding] [transition-duration:240ms] [transition-timing-function:cubic-bezier(0.4,0,0.2,1)] motion-reduce:transition-none"
+          :class="sidebarCollapsed ? 'h-16 px-4' : 'h-20 px-6'"
         >
-          <HeaderLogo
-            size="h-9 w-9"
-            class-name="text-[#191919] dark:text-white"
-          />
-          <div class="flex flex-col justify-center">
-            <h1 class="text-lg font-bold text-[#191919] dark:text-white leading-none">
-              {{ siteName }}
-            </h1>
-            <span class="text-[10px] text-[#91918d] dark:text-muted-foreground leading-none mt-1.5 font-medium tracking-wide">{{ siteSubtitle }}</span>
-          </div>
-        </RouterLink>
-      </div>
-
-      <!-- NAVIGATION -->
-      <div class="flex-1 overflow-y-auto py-2 scrollbar-none">
-        <SidebarNav
-          :items="navigation"
-          :is-active="isNavActive"
-          @prefetch="prefetchNavigationItem"
-        />
-      </div>
-
-      <!-- FOOTER (Profile) -->
-      <div class="p-4 border-t border-[#3d3929]/5 dark:border-white/5">
-        <div class="flex items-center justify-between p-2 rounded-xl">
-          <div class="flex items-center gap-3 min-w-0">
-            <div class="w-8 h-8 rounded-full bg-[#f0f0eb] dark:bg-white/10 border border-black/5 flex items-center justify-center text-xs font-bold text-[#3d3929] dark:text-[#d4a27f] shrink-0">
-              {{ authStore.user?.username?.substring(0, 2).toUpperCase() }}
-            </div>
-            <div class="flex flex-col min-w-0">
-              <span class="text-xs font-semibold leading-none truncate opacity-90 text-foreground">{{ authStore.user?.username }}</span>
-              <span class="text-[10px] opacity-50 leading-none mt-1.5 text-muted-foreground">{{ currentRoleLabel }}</span>
-            </div>
-          </div>
-
-          <div class="flex items-center gap-1">
+          <Transition
+            name="sidebar-mode"
+            mode="out-in"
+          >
             <RouterLink
-              to="/dashboard/settings"
-              class="p-1.5 hover:bg-muted/50 rounded-md text-muted-foreground hover:text-foreground transition-colors"
-              :title="t('common.settings')"
+              v-if="!sidebarCollapsed"
+              key="expanded-brand"
+              to="/"
+              class="group flex w-full min-w-0 items-center gap-3 pr-10 transition-opacity hover:opacity-80"
             >
-              <Settings class="w-4 h-4" />
+              <HeaderLogo
+                size="h-9 w-9"
+                class-name="shrink-0 text-[#191919] dark:text-white"
+              />
+              <div class="flex min-w-0 flex-col justify-center">
+                <h1 class="truncate text-lg font-bold leading-none text-[#191919] dark:text-white">
+                  {{ siteName }}
+                </h1>
+                <span class="mt-1.5 truncate text-[10px] font-medium leading-none tracking-wide text-[#91918d] dark:text-muted-foreground">{{ siteSubtitle }}</span>
+              </div>
             </RouterLink>
-            <button
-              class="p-1.5 rounded-md text-muted-foreground hover:text-red-500 transition-colors"
-              :title="t('common.logout')"
-              @click="handleLogout"
+
+            <div
+              v-else
+              key="collapsed-brand"
+              aria-hidden="true"
+              class="flex h-8 w-8 transform-gpu items-center justify-center transition-[opacity,transform] duration-200 ease-out will-change-[opacity,transform] group-hover/sidebar-brand:scale-90 group-hover/sidebar-brand:opacity-0 motion-reduce:transition-none"
             >
-              <LogOut class="w-4 h-4" />
-            </button>
-          </div>
+              <HeaderLogo
+                size="h-8 w-8"
+                class-name="shrink-0 text-[#191919] dark:text-white"
+              />
+            </div>
+          </Transition>
+
+          <button
+            type="button"
+            class="absolute top-1/2 z-10 flex h-8 w-8 shrink-0 -translate-y-1/2 transform-gpu items-center justify-center rounded-md text-muted-foreground transition-[right,color,background-color,opacity,transform] [transition-duration:240ms] [transition-timing-function:cubic-bezier(0.4,0,0.2,1)] hover:bg-muted/50 hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary motion-reduce:transition-none"
+            :class="sidebarCollapsed ? 'right-[15px] scale-90 opacity-0 will-change-[right,opacity,transform] group-hover/sidebar-brand:scale-100 group-hover/sidebar-brand:opacity-100 focus-visible:scale-100 focus-visible:bg-[#faf9f5] focus-visible:opacity-100 dark:focus-visible:bg-[#1e1c19]' : 'right-6 opacity-100'"
+            :aria-label="sidebarCollapsed ? t('nav.expandSidebar') : t('nav.collapseSidebar')"
+            :aria-expanded="!sidebarCollapsed"
+            :title="sidebarCollapsed ? t('nav.expandSidebar') : t('nav.collapseSidebar')"
+            @click="sidebarCollapsed = !sidebarCollapsed"
+          >
+            <Transition
+              name="sidebar-icon"
+              mode="out-in"
+            >
+              <PanelLeftOpen
+                v-if="sidebarCollapsed"
+                key="open"
+                class="h-4 w-4"
+              />
+              <PanelLeftClose
+                v-else
+                key="close"
+                class="h-4 w-4"
+              />
+            </Transition>
+          </button>
         </div>
+
+        <!-- NAVIGATION -->
+        <div
+          class="flex-1 overflow-y-auto transition-[padding] [transition-duration:240ms] [transition-timing-function:cubic-bezier(0.4,0,0.2,1)] scrollbar-none motion-reduce:transition-none"
+          :class="sidebarCollapsed ? 'pb-2 pt-0' : 'py-2'"
+        >
+          <Transition
+            name="sidebar-mode"
+            mode="out-in"
+          >
+            <div
+              :key="sidebarCollapsed ? 'collapsed-nav' : 'expanded-nav'"
+              class="w-full"
+              :class="sidebarCollapsed ? 'max-w-16' : ''"
+            >
+              <SidebarNav
+                :items="navigation"
+                :is-active="isNavActive"
+                :collapsed="sidebarCollapsed"
+                @prefetch="prefetchNavigationItem"
+              />
+            </div>
+          </Transition>
+        </div>
+
+        <!-- FOOTER (Profile) -->
+        <Transition
+          name="sidebar-mode"
+          mode="out-in"
+        >
+          <div
+            :key="sidebarCollapsed ? 'collapsed-footer' : 'expanded-footer'"
+            class="border-t border-[#3d3929]/5 dark:border-white/5"
+            :class="sidebarCollapsed ? 'max-w-16 p-2' : 'p-4'"
+          >
+            <div
+              class="flex items-center"
+              :class="sidebarCollapsed ? 'flex-col gap-2 rounded-lg p-1' : 'justify-between rounded-xl p-2'"
+            >
+              <div
+                class="flex min-w-0 items-center"
+                :class="sidebarCollapsed ? 'justify-center' : 'gap-3'"
+              >
+                <div
+                  class="flex h-8 w-8 shrink-0 items-center justify-center rounded-full border border-black/5 bg-[#f0f0eb] text-xs font-bold text-[#3d3929] dark:bg-white/10 dark:text-[#d4a27f]"
+                  :title="sidebarCollapsed ? authStore.user?.username : undefined"
+                >
+                  {{ authStore.user?.username?.substring(0, 2).toUpperCase() }}
+                </div>
+                <div
+                  v-if="!sidebarCollapsed"
+                  class="flex min-w-0 flex-col"
+                >
+                  <span class="truncate text-xs font-semibold leading-none text-foreground opacity-90">{{ authStore.user?.username }}</span>
+                  <span class="mt-1.5 text-[10px] leading-none text-muted-foreground opacity-50">{{ currentRoleLabel }}</span>
+                </div>
+              </div>
+
+              <div
+                class="flex items-center gap-1"
+                :class="sidebarCollapsed ? 'flex-col' : ''"
+              >
+                <RouterLink
+                  to="/dashboard/settings"
+                  class="rounded-md p-1.5 text-muted-foreground transition-colors hover:bg-muted/50 hover:text-foreground"
+                  :aria-label="sidebarCollapsed ? t('common.settings') : undefined"
+                  :title="t('common.settings')"
+                >
+                  <Settings class="h-4 w-4" />
+                </RouterLink>
+                <button
+                  class="rounded-md p-1.5 text-muted-foreground transition-colors hover:text-red-500"
+                  :aria-label="sidebarCollapsed ? t('common.logout') : undefined"
+                  :title="t('common.logout')"
+                  @click="handleLogout"
+                >
+                  <LogOut class="h-4 w-4" />
+                </button>
+              </div>
+            </div>
+          </div>
+        </Transition>
       </div>
     </template>
 
@@ -392,6 +483,7 @@
 
 <script setup lang="ts">
 import { computed, ref, watch, onMounted, onUnmounted } from 'vue'
+import { useLocalStorage } from '@vueuse/core'
 import { useRoute, useRouter } from 'vue-router'
 import { marked } from 'marked'
 import { useAuthStore } from '@/stores/auth'
@@ -419,6 +511,8 @@ import {
   ChevronRight,
   Menu,
   X,
+  PanelLeftClose,
+  PanelLeftOpen,
 } from 'lucide-vue-next'
 
 import GithubIcon from '@/components/icons/GithubIcon.vue'
@@ -441,6 +535,7 @@ const isAdmin = computed(() => authStore.user?.role === 'admin')
 
 const showAuthError = ref(false)
 const mobileMenuOpen = ref(false)
+const sidebarCollapsed = useLocalStorage('aether-sidebar-collapsed', false)
 const requiredAnnouncements = ref<Announcement[]>([])
 const acknowledgingRequiredAnnouncement = ref(false)
 const requiredAnnouncementOpen = computed({
@@ -1143,8 +1238,8 @@ const breadcrumbs = computed(() => buildBreadcrumbs({
 
 // Styling Classes (Editorial)
 const sidebarClasses = computed(() => {
-    // Fixed width, border right, background match
-    return `w-[260px] flex flex-col hidden lg:flex border-r border-[#3d3929]/5 dark:border-white/5 bg-[#faf9f5] dark:bg-[#1e1c19] h-screen sticky top-0`
+    const widthClass = sidebarCollapsed.value ? 'w-16' : 'w-[260px]'
+    return `${widthClass} flex-col hidden lg:flex border-r border-[#3d3929]/5 dark:border-white/5 bg-[#faf9f5] dark:bg-[#1e1c19] h-screen sticky top-0 transition-[width] [transition-duration:240ms] [transition-timing-function:cubic-bezier(0.4,0,0.2,1)] motion-reduce:transition-none`
 })
 
 const contentClasses = computed(() => {
@@ -1160,6 +1255,38 @@ const mainClasses = computed(() => {
 </script>
 
 <style scoped>
+.sidebar-mode-enter-active {
+  transition: opacity 120ms ease-out;
+}
+
+.sidebar-mode-leave-active {
+  transition: opacity 60ms ease-in;
+}
+
+.sidebar-mode-enter-from,
+.sidebar-mode-leave-to {
+  opacity: 0;
+}
+
+.sidebar-icon-enter-active,
+.sidebar-icon-leave-active {
+  transition: opacity 60ms ease;
+}
+
+.sidebar-icon-enter-from,
+.sidebar-icon-leave-to {
+  opacity: 0;
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .sidebar-mode-enter-active,
+  .sidebar-mode-leave-active,
+  .sidebar-icon-enter-active,
+  .sidebar-icon-leave-active {
+    transition: none;
+  }
+}
+
 .scrollbar-none::-webkit-scrollbar { display: none; }
 .scrollbar-none { -ms-overflow-style: none; scrollbar-width: none; }
 </style>