diff --git a/frontend/src/api/client.js b/frontend/src/api/client.js
index f6f5f54..d466746 100644
--- a/frontend/src/api/client.js
+++ b/frontend/src/api/client.js
@@ -290,6 +290,27 @@ export function adminDeleteUser(id, adminPassword) {
   })
 }
 
+// ── System AI Provider Configuration (D-08, D-15) ───────────────────────────
+
+export function getAiConfig() {
+  return request('/api/admin/ai-config', { method: 'GET' })
+}
+
+export function saveAiConfig(body) {
+  return request('/api/admin/ai-config', {
+    method: 'PUT',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(body),
+  })
+}
+
+export function testAiConnection(providerId) {
+  return request(
+    '/api/admin/ai-config/test-connection?provider_id=' + encodeURIComponent(providerId),
+    { method: 'GET' }
+  )
+}
+
 // ── Folders ───────────────────────────────────────────────────────────────────
 
 export function listFolders(parentId = null) {
diff --git a/frontend/src/components/admin/AdminAiConfigTab.vue b/frontend/src/components/admin/AdminAiConfigTab.vue
index afee257..334751b 100644
--- a/frontend/src/components/admin/AdminAiConfigTab.vue
+++ b/frontend/src/components/admin/AdminAiConfigTab.vue
@@ -1,5 +1,150 @@
 <template>
   <div>
+    <!-- ── System AI Providers (Global) ───────────────────────────────────── -->
+    <section class="bg-white rounded-xl border border-gray-200 overflow-hidden mb-6">
+      <div class="px-6 py-4 border-b border-gray-200">
+        <h2 class="text-sm font-semibold text-gray-900">System AI Providers (Global)</h2>
+        <p class="text-xs text-gray-500 mt-0.5">
+          These settings apply to all classification jobs. Per-user overrides below take precedence when set.
+        </p>
+      </div>
+
+      <!-- Loading spinner -->
+      <div v-if="loadingSystem" class="p-6 text-center">
+        <div class="flex items-center justify-center gap-2 text-gray-400 text-sm">
+          <span class="animate-spin rounded-full border-2 border-current border-t-transparent w-4 h-4"></span>
+          Loading AI providers…
+        </div>
+      </div>
+
+      <!-- System error banner -->
+      <div v-if="systemError" class="mx-6 mt-4 px-4 py-3 bg-red-50 border border-red-200 rounded-lg text-sm text-red-700">
+        {{ systemError }}
+      </div>
+
+      <!-- Provider accordion list -->
+      <div v-if="!loadingSystem" class="divide-y divide-gray-100">
+        <div
+          v-for="prov in systemProviders"
+          :key="prov.provider_id"
+          :class="['transition-colors', prov.is_active ? 'border-l-4 border-l-green-500' : '']"
+        >
+          <!-- Accordion header -->
+          <button
+            class="w-full flex items-center justify-between px-6 py-3 text-left hover:bg-gray-50 transition-colors"
+            @click="toggleProvider(prov.provider_id)"
+          >
+            <div class="flex items-center gap-3">
+              <span class="text-sm font-medium text-gray-900 capitalize">{{ prov.provider_id }}</span>
+              <span
+                v-if="prov.is_active"
+                class="bg-green-100 text-green-700 text-xs font-semibold px-2 py-0.5 rounded-full"
+              >Active</span>
+            </div>
+            <svg
+              :class="['w-4 h-4 text-gray-400 transition-transform', openProviderId === prov.provider_id ? 'rotate-180' : '']"
+              fill="none" stroke="currentColor" viewBox="0 0 24 24"
+            >
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M19 9l-7 7-7-7" />
+            </svg>
+          </button>
+
+          <!-- Accordion body -->
+          <div v-if="openProviderId === prov.provider_id" class="px-6 pb-5 pt-2 bg-gray-50 space-y-3">
+            <!-- API Key -->
+            <div>
+              <label class="block text-xs font-medium text-gray-600 mb-1">API Key</label>
+              <input
+                v-model="formByProvider[prov.provider_id].api_key"
+                type="password"
+                :placeholder="prov.has_api_key ? '(unchanged)' : '(not set)'"
+                autocomplete="off"
+                class="block w-full rounded-lg px-3 py-2 text-sm border border-gray-300 focus:outline-none focus:ring-2 focus:ring-indigo-500 focus:border-indigo-500 transition-colors"
+              />
+            </div>
+
+            <!-- Base URL -->
+            <div>
+              <label class="block text-xs font-medium text-gray-600 mb-1">Base URL</label>
+              <input
+                v-model="formByProvider[prov.provider_id].base_url"
+                type="text"
+                :placeholder="providerDefaultBaseUrl(prov.provider_id) || '(default)'"
+                class="block w-full rounded-lg px-3 py-2 text-sm border border-gray-300 focus:outline-none focus:ring-2 focus:ring-indigo-500 focus:border-indigo-500 transition-colors"
+              />
+            </div>
+
+            <!-- Model name -->
+            <div>
+              <label class="block text-xs font-medium text-gray-600 mb-1">Model Name</label>
+              <input
+                v-model="formByProvider[prov.provider_id].model_name"
+                type="text"
+                :placeholder="providerDefaultModel(prov.provider_id)"
+                class="block w-full rounded-lg px-3 py-2 text-sm border border-gray-300 focus:outline-none focus:ring-2 focus:ring-indigo-500 focus:border-indigo-500 transition-colors"
+              />
+            </div>
+
+            <!-- Context chars -->
+            <div>
+              <label class="block text-xs font-medium text-gray-600 mb-1">Context Characters</label>
+              <input
+                v-model.number="formByProvider[prov.provider_id].context_chars"
+                type="number"
+                :placeholder="String(providerDefaultContextChars(prov.provider_id))"
+                min="1000"
+                max="2000000"
+                class="block w-full rounded-lg px-3 py-2 text-sm border border-gray-300 focus:outline-none focus:ring-2 focus:ring-indigo-500 focus:border-indigo-500 transition-colors"
+              />
+            </div>
+
+            <!-- Action buttons -->
+            <div class="flex items-center gap-2 pt-1">
+              <!-- Set Active -->
+              <button
+                @click="saveSystemProvider(prov.provider_id, { activate: true })"
+                :disabled="savingProvider === prov.provider_id || prov.is_active"
+                class="text-xs bg-green-600 text-white font-semibold px-3 py-1.5 rounded-lg hover:bg-green-700 disabled:opacity-50 transition-colors"
+              >
+                Set Active
+              </button>
+
+              <!-- Save -->
+              <button
+                @click="saveSystemProvider(prov.provider_id)"
+                :disabled="savingProvider === prov.provider_id"
+                class="text-xs bg-indigo-600 text-white font-semibold px-3 py-1.5 rounded-lg hover:bg-indigo-700 disabled:opacity-50 flex items-center gap-1 transition-colors"
+              >
+                <span v-if="savingProvider === prov.provider_id" class="animate-spin rounded-full border-2 border-current border-t-transparent w-3 h-3"></span>
+                {{ savingProvider === prov.provider_id ? 'Saving…' : 'Save' }}
+              </button>
+
+              <!-- Test Connection -->
+              <button
+                @click="runTestConnection(prov.provider_id)"
+                :disabled="savingProvider === prov.provider_id"
+                class="text-xs border border-gray-300 text-gray-700 font-semibold px-3 py-1.5 rounded-lg hover:bg-gray-100 disabled:opacity-50 transition-colors"
+              >
+                Test Connection
+              </button>
+
+              <!-- Test result badge -->
+              <span
+                v-if="testResults[prov.provider_id] === 'ok'"
+                class="text-xs bg-green-100 text-green-700 font-semibold px-2 py-1 rounded-full"
+              >OK</span>
+              <span
+                v-else-if="testResults[prov.provider_id] === 'failed'"
+                class="text-xs bg-red-100 text-red-700 font-semibold px-2 py-1 rounded-full"
+              >Failed</span>
+            </div>
+          </div>
+        </div>
+      </div>
+    </section>
+
+    <!-- ── Per-user AI provider assignment (existing — DO NOT MODIFY) ─────── -->
+
     <!-- Loading state -->
     <div v-if="loading" class="bg-white rounded-xl border border-gray-200 p-8 text-center">
       <div class="flex items-center justify-center gap-2 text-gray-400 text-sm">
@@ -76,6 +221,99 @@
 <script setup>
 import { ref, reactive, onMounted } from 'vue'
 import * as api from '../../api/client.js'
+import { getAiConfig, saveAiConfig, testAiConnection } from '../../api/client.js'
+
+// ── Per-provider default lookup (mirrors backend PROVIDER_DEFAULTS) ───────────
+
+const _PROVIDER_DEFAULTS = {
+  openai:     { base_url: null,                                                       model: 'gpt-4o',                           context_chars: 120000 },
+  anthropic:  { base_url: null,                                                       model: 'claude-sonnet-4-6',                context_chars: 180000 },
+  gemini:     { base_url: 'https://generativelanguage.googleapis.com/v1beta/openai/', model: 'gemini-2.0-flash',                 context_chars: 800000 },
+  groq:       { base_url: 'https://api.groq.com/openai/v1',                          model: 'llama-3.3-70b-versatile',          context_chars: 128000 },
+  xai:        { base_url: 'https://api.x.ai/v1',                                     model: 'grok-3-mini',                      context_chars: 128000 },
+  deepseek:   { base_url: 'https://api.deepseek.com',                                model: 'deepseek-chat',                    context_chars: 60000  },
+  openrouter: { base_url: 'https://openrouter.ai/api/v1',                             model: 'anthropic/claude-3.5-sonnet',      context_chars: 180000 },
+  mistral:    { base_url: 'https://api.mistral.ai/v1',                               model: 'mistral-large-latest',             context_chars: 128000 },
+  ollama:     { base_url: 'http://host.docker.internal:11434/v1',                    model: 'llama3.2',                         context_chars: 8000   },
+  lmstudio:   { base_url: 'http://host.docker.internal:1234/v1',                     model: 'gemma-4-e4b-it',                   context_chars: 8000   },
+}
+
+function providerDefaultBaseUrl(pid) { return _PROVIDER_DEFAULTS[pid]?.base_url || '' }
+function providerDefaultModel(pid)   { return _PROVIDER_DEFAULTS[pid]?.model || '' }
+function providerDefaultContextChars(pid) { return _PROVIDER_DEFAULTS[pid]?.context_chars || 8000 }
+
+// ── System provider state ─────────────────────────────────────────────────────
+
+const systemProviders = ref([])
+const loadingSystem = ref(false)
+const systemError = ref(null)
+const openProviderId = ref(null)
+const formByProvider = reactive({})
+const testResults = reactive({})
+const savingProvider = ref(null)
+
+function toggleProvider(pid) {
+  openProviderId.value = openProviderId.value === pid ? null : pid
+}
+
+function _initForm(prov) {
+  formByProvider[prov.provider_id] = {
+    api_key: '',             // write-only: never pre-filled from server
+    base_url: prov.base_url || '',
+    model_name: prov.model_name || '',
+    context_chars: prov.context_chars || 0,
+  }
+}
+
+async function loadSystemProviders() {
+  loadingSystem.value = true
+  systemError.value = null
+  try {
+    const data = await getAiConfig()
+    systemProviders.value = data.providers || []
+    for (const prov of systemProviders.value) {
+      _initForm(prov)
+    }
+  } catch (e) {
+    systemError.value = e.message || 'Failed to load AI provider config'
+  } finally {
+    loadingSystem.value = false
+  }
+}
+
+async function saveSystemProvider(providerId, opts = {}) {
+  savingProvider.value = providerId
+  const form = formByProvider[providerId] || {}
+  const body = { provider_id: providerId }
+
+  // Only include fields the admin actually modified (api_key only if user typed something)
+  if (form.api_key !== '') body.api_key = form.api_key
+  if (form.base_url !== '') body.base_url = form.base_url
+  if (form.model_name !== '') body.model_name = form.model_name
+  if (form.context_chars && form.context_chars !== 0) body.context_chars = form.context_chars
+  if (opts.activate) body.is_active = true
+
+  try {
+    await saveAiConfig(body)
+    await loadSystemProviders()
+  } catch (e) {
+    systemError.value = e.message || 'Failed to save provider config'
+  } finally {
+    savingProvider.value = null
+  }
+}
+
+async function runTestConnection(providerId) {
+  try {
+    const r = await testAiConnection(providerId)
+    testResults[providerId] = r.ok ? 'ok' : 'failed'
+  } catch {
+    testResults[providerId] = 'failed'
+  }
+  setTimeout(() => { testResults[providerId] = null }, 3000)
+}
+
+// ── Per-user assignment state (existing — DO NOT MODIFY) ──────────────────────
 
 const users = ref([])
 const loading = ref(false)
@@ -114,6 +352,9 @@ async function saveConfig(userId) {
 }
 
 onMounted(async () => {
+  // Load system providers AND per-user list in parallel
+  loadSystemProviders()
+
   loading.value = true
   loadError.value = null
   try {
diff --git a/frontend/tests/api.spec.js b/frontend/tests/api.spec.js
new file mode 100644
index 0000000..c64a8e6
--- /dev/null
+++ b/frontend/tests/api.spec.js
@@ -0,0 +1,84 @@
+/**
+ * Vitest unit tests for the system AI provider client helpers.
+ *
+ * Tests verify that getAiConfig, saveAiConfig, and testAiConnection
+ * construct the correct fetch payloads (path, method, body, encoding).
+ *
+ * D-11 frontend coverage — CLAUDE.md mandate: every new function has at least one test.
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest'
+
+// ── Mock Pinia auth store (request() lazy-imports it) ────────────────────────
+// The request() helper in client.js does:
+//   const { useAuthStore } = await import('../stores/auth.js')
+//   const authStore = useAuthStore()
+// We stub the module so it returns a store with no accessToken,
+// preventing Pinia initialization in unit tests.
+vi.mock('../src/stores/auth.js', () => ({
+  useAuthStore: () => ({ accessToken: null }),
+}))
+
+// ── Mock global fetch ─────────────────────────────────────────────────────────
+let fetchMock
+
+beforeEach(() => {
+  fetchMock = vi.fn(() =>
+    Promise.resolve(
+      new Response(JSON.stringify({ ok: true }), {
+        status: 200,
+        headers: { 'Content-Type': 'application/json' },
+      })
+    )
+  )
+  vi.stubGlobal('fetch', fetchMock)
+})
+
+// ── Import helpers under test ─────────────────────────────────────────────────
+import { getAiConfig, saveAiConfig, testAiConnection } from '../src/api/client.js'
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe('getAiConfig', () => {
+  it('issues GET /api/admin/ai-config', async () => {
+    await getAiConfig()
+
+    expect(fetchMock).toHaveBeenCalledOnce()
+    const [url, init] = fetchMock.mock.calls[0]
+    expect(url).toMatch(/\/api\/admin\/ai-config$/)
+    expect(init.method).toBe('GET')
+  })
+})
+
+describe('saveAiConfig', () => {
+  it('issues PUT with JSON body containing provider_id and api_key', async () => {
+    const payload = { provider_id: 'openai', api_key: 'sk-x' }
+    await saveAiConfig(payload)
+
+    expect(fetchMock).toHaveBeenCalledOnce()
+    const [url, init] = fetchMock.mock.calls[0]
+    expect(url).toMatch(/\/api\/admin\/ai-config$/)
+    expect(init.method).toBe('PUT')
+    expect(init.headers?.['Content-Type'] || init.headers?.get?.('Content-Type')).toBe('application/json')
+    expect(JSON.parse(init.body)).toEqual({ provider_id: 'openai', api_key: 'sk-x' })
+  })
+})
+
+describe('testAiConnection', () => {
+  it('issues GET with URL-encoded provider_id', async () => {
+    // Provider ID with a space to verify encodeURIComponent is applied
+    await testAiConnection('open ai')
+
+    expect(fetchMock).toHaveBeenCalledOnce()
+    const [url, init] = fetchMock.mock.calls[0]
+    expect(url).toContain('/api/admin/ai-config/test-connection?provider_id=open%20ai')
+    expect(init.method).toBe('GET')
+  })
+
+  it('issues GET with a plain provider_id that needs no encoding', async () => {
+    await testAiConnection('openai')
+
+    const [url] = fetchMock.mock.calls[0]
+    expect(url).toContain('/api/admin/ai-config/test-connection?provider_id=openai')
+  })
+})