diff --git a/dev-api.py b/dev-api.py
index 1e3b968..d74c738 100644
--- a/dev-api.py
+++ b/dev-api.py
@@ -1142,3 +1142,50 @@ def suggest_search(body: dict):
         return {"suggestions": []}
     except Exception as e:
         raise HTTPException(status_code=500, detail=str(e))
+
+
+# ── Settings: System — LLM Backends + BYOK endpoints ─────────────────────────
+
+class ByokAckPayload(BaseModel):
+    backends: List[str] = []
+
+LLM_CONFIG_PATH = Path("config/llm.yaml")
+
+@app.get("/api/settings/system/llm")
+def get_llm_config():
+    try:
+        user = load_user_profile(_user_yaml_path())
+        backends = []
+        if LLM_CONFIG_PATH.exists():
+            with open(LLM_CONFIG_PATH) as f:
+                data = yaml.safe_load(f) or {}
+            backends = data.get("backends", [])
+        return {"backends": backends, "byok_acknowledged": user.get("byok_acknowledged_backends", [])}
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=str(e))
+
+@app.put("/api/settings/system/llm")
+def save_llm_config(payload: dict):
+    try:
+        data = {}
+        if LLM_CONFIG_PATH.exists():
+            with open(LLM_CONFIG_PATH) as f:
+                data = yaml.safe_load(f) or {}
+        data["backends"] = payload.get("backends", [])
+        LLM_CONFIG_PATH.parent.mkdir(parents=True, exist_ok=True)
+        with open(LLM_CONFIG_PATH, "w") as f:
+            yaml.dump(data, f, allow_unicode=True, default_flow_style=False)
+        return {"ok": True}
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=str(e))
+
+@app.post("/api/settings/system/llm/byok-ack")
+def byok_ack(payload: ByokAckPayload):
+    try:
+        user = load_user_profile(_user_yaml_path())
+        existing = user.get("byok_acknowledged_backends", [])
+        user["byok_acknowledged_backends"] = list(set(existing + payload.backends))
+        save_user_profile(_user_yaml_path(), user)
+        return {"ok": True}
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=str(e))
diff --git a/web/src/stores/settings/system.test.ts b/web/src/stores/settings/system.test.ts
new file mode 100644
index 0000000..c4ececc
--- /dev/null
+++ b/web/src/stores/settings/system.test.ts
@@ -0,0 +1,62 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest'
+import { setActivePinia, createPinia } from 'pinia'
+import { useSystemStore } from './system'
+
+vi.mock('../../composables/useApi', () => ({ useApiFetch: vi.fn() }))
+import { useApiFetch } from '../../composables/useApi'
+const mockFetch = vi.mocked(useApiFetch)
+
+describe('useSystemStore — BYOK gate', () => {
+  beforeEach(() => { setActivePinia(createPinia()); vi.clearAllMocks() })
+
+  it('save() proceeds without modal when no cloud backends enabled', async () => {
+    mockFetch.mockResolvedValue({ data: { ok: true }, error: null })
+    const store = useSystemStore()
+    store.backends = [{ id: 'ollama', enabled: true, priority: 1 }]
+    store.byokAcknowledged = []
+    await store.trySave()
+    expect(store.byokPending).toHaveLength(0)
+    expect(mockFetch).toHaveBeenCalledWith('/api/settings/system/llm', expect.anything())
+  })
+
+  it('save() sets byokPending when new cloud backend enabled', async () => {
+    const store = useSystemStore()
+    store.backends = [{ id: 'anthropic', enabled: true, priority: 1 }]
+    store.byokAcknowledged = []
+    await store.trySave()
+    expect(store.byokPending).toContain('anthropic')
+    expect(mockFetch).not.toHaveBeenCalledWith('/api/settings/system/llm', expect.anything())
+  })
+
+  it('save() skips modal for already-acknowledged backends', async () => {
+    mockFetch.mockResolvedValue({ data: { ok: true }, error: null })
+    const store = useSystemStore()
+    store.backends = [{ id: 'anthropic', enabled: true, priority: 1 }]
+    store.byokAcknowledged = ['anthropic']
+    await store.trySave()
+    expect(store.byokPending).toHaveLength(0)
+  })
+
+  it('confirmByok() saves acknowledgment then commits LLM config', async () => {
+    mockFetch.mockResolvedValue({ data: { ok: true }, error: null })
+    const store = useSystemStore()
+    store.byokPending = ['anthropic']
+    store.backends = [{ id: 'anthropic', enabled: true, priority: 1 }]
+    await store.confirmByok()
+    expect(mockFetch).toHaveBeenCalledWith('/api/settings/system/llm/byok-ack', expect.anything())
+    expect(mockFetch).toHaveBeenCalledWith('/api/settings/system/llm', expect.anything())
+  })
+
+  it('cancelByok() clears pending and restores backends to pre-save state', async () => {
+    mockFetch.mockResolvedValue({ data: { ok: true }, error: null })
+    const store = useSystemStore()
+    const original = [{ id: 'ollama', enabled: true, priority: 1 }]
+    store.backends = [...original]
+    await store.trySave()  // captures snapshot, commits (no cloud backends)
+    store.backends = [{ id: 'anthropic', enabled: true, priority: 1 }]
+    store.byokPending = ['anthropic']
+    store.cancelByok()
+    expect(store.byokPending).toHaveLength(0)
+    expect(store.backends).toEqual(original)
+  })
+})
diff --git a/web/src/stores/settings/system.ts b/web/src/stores/settings/system.ts
new file mode 100644
index 0000000..f3fea40
--- /dev/null
+++ b/web/src/stores/settings/system.ts
@@ -0,0 +1,73 @@
+import { ref } from 'vue'
+import { defineStore } from 'pinia'
+import { useApiFetch } from '../../composables/useApi'
+
+const CLOUD_BACKEND_IDS = ['anthropic', 'openai']
+
+export interface Backend { id: string; enabled: boolean; priority: number }
+
+export const useSystemStore = defineStore('settings/system', () => {
+  const backends = ref<Backend[]>([])
+  const byokAcknowledged = ref<string[]>([])
+  const byokPending = ref<string[]>([])
+  // Private snapshot — NOT in return(). Closure-level only.
+  let _preSaveSnapshot: Backend[] = []
+  const saving = ref(false)
+  const saveError = ref<string | null>(null)
+  const loadError = ref<string | null>(null)
+
+  async function loadLlm() {
+    loadError.value = null
+    const { data, error } = await useApiFetch<{ backends: Backend[]; byok_acknowledged: string[] }>('/api/settings/system/llm')
+    if (error) { loadError.value = 'Failed to load LLM config'; return }
+    if (!data) return
+    backends.value = data.backends ?? []
+    byokAcknowledged.value = data.byok_acknowledged ?? []
+  }
+
+  async function trySave() {
+    _preSaveSnapshot = JSON.parse(JSON.stringify(backends.value))
+    const newlyEnabled = backends.value
+      .filter(b => CLOUD_BACKEND_IDS.includes(b.id) && b.enabled)
+      .map(b => b.id)
+      .filter(id => !byokAcknowledged.value.includes(id))
+    if (newlyEnabled.length > 0) {
+      byokPending.value = newlyEnabled
+      return  // modal takes over
+    }
+    await _commitSave()
+  }
+
+  async function confirmByok() {
+    saving.value = true
+    const { error } = await useApiFetch('/api/settings/system/llm/byok-ack', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ backends: byokPending.value }),
+    })
+    if (!error) byokAcknowledged.value = [...byokAcknowledged.value, ...byokPending.value]
+    byokPending.value = []
+    await _commitSave()
+  }
+
+  function cancelByok() {
+    backends.value = JSON.parse(JSON.stringify(_preSaveSnapshot))
+    byokPending.value = []
+    _preSaveSnapshot = []
+  }
+
+  async function _commitSave() {
+    saving.value = true
+    saveError.value = null
+    const { error } = await useApiFetch('/api/settings/system/llm', {
+      method: 'PUT',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ backends: backends.value }),
+    })
+    saving.value = false
+    if (error) saveError.value = 'Save failed — please try again.'
+  }
+
+  // Services, email, integrations added in Task 6
+  return { backends, byokAcknowledged, byokPending, saving, saveError, loadError, loadLlm, trySave, confirmByok, cancelByok }
+})
diff --git a/web/src/views/settings/SystemSettingsView.vue b/web/src/views/settings/SystemSettingsView.vue
new file mode 100644
index 0000000..e0e4433
--- /dev/null
+++ b/web/src/views/settings/SystemSettingsView.vue
@@ -0,0 +1,154 @@
+<template>
+  <div class="system-settings">
+    <h2>System Settings</h2>
+    <p class="tab-note">This tab is only available in self-hosted mode.</p>
+
+    <p v-if="store.loadError" class="error-banner">{{ store.loadError }}</p>
+
+    <!-- LLM Backends -->
+    <section class="form-section">
+      <h3>LLM Backends</h3>
+      <p class="section-note">Drag to reorder. Higher position = higher priority in the fallback chain.</p>
+
+      <div class="backend-list">
+        <div
+          v-for="(backend, idx) in visibleBackends"
+          :key="backend.id"
+          class="backend-card"
+          draggable="true"
+          @dragstart="dragStart(idx)"
+          @dragover.prevent="dragOver(idx)"
+          @drop="drop"
+        >
+          <span class="drag-handle" aria-hidden="true">⠿</span>
+          <span class="priority-badge">{{ idx + 1 }}</span>
+          <span class="backend-id">{{ backend.id }}</span>
+          <label class="toggle-label">
+            <input
+              type="checkbox"
+              :checked="backend.enabled"
+              @change="store.backends = store.backends.map(b =>
+                b.id === backend.id ? { ...b, enabled: !b.enabled } : b
+              )"
+            />
+            <span class="toggle-text">{{ backend.enabled ? 'Enabled' : 'Disabled' }}</span>
+          </label>
+        </div>
+      </div>
+
+      <div class="form-actions">
+        <button @click="store.trySave()" :disabled="store.saving" class="btn-primary">
+          {{ store.saving ? 'Saving…' : 'Save Backends' }}
+        </button>
+        <p v-if="store.saveError" class="error">{{ store.saveError }}</p>
+      </div>
+    </section>
+
+    <!-- BYOK Modal -->
+    <Teleport to="body">
+      <div v-if="store.byokPending.length > 0" class="modal-overlay" @click.self="store.cancelByok()">
+        <div class="modal-card" role="dialog" aria-modal="true" aria-labelledby="byok-title">
+          <h3 id="byok-title">⚠️ Cloud LLM Key Required</h3>
+          <p>You are enabling the following cloud backends:</p>
+          <ul>
+            <li v-for="b in store.byokPending" :key="b">{{ b }}</li>
+          </ul>
+          <p class="byok-warning">
+            These services require your own API key. Your requests and data will be
+            sent to these third-party providers. Costs will be charged to your account.
+          </p>
+          <label class="checkbox-row">
+            <input type="checkbox" v-model="byokConfirmed" />
+            I understand and have configured my API key in <code>config/llm.yaml</code>
+          </label>
+          <div class="modal-actions">
+            <button @click="store.cancelByok()" class="btn-cancel">Cancel</button>
+            <button
+              @click="handleConfirmByok"
+              :disabled="!byokConfirmed || store.saving"
+              class="btn-primary"
+            >{{ store.saving ? 'Saving…' : 'Save with Cloud LLM' }}</button>
+          </div>
+        </div>
+      </div>
+    </Teleport>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { ref, computed, onMounted } from 'vue'
+import { useSystemStore } from '../../stores/settings/system'
+import { useAppConfigStore } from '../../stores/appConfig'
+
+const store = useSystemStore()
+const config = useAppConfigStore()
+
+const byokConfirmed = ref(false)
+const dragIdx = ref<number | null>(null)
+
+const CONTRACTED_ONLY = ['claude-code', 'copilot']
+
+const visibleBackends = computed(() =>
+  store.backends.filter(b =>
+    !CONTRACTED_ONLY.includes(b.id) || config.contractedClient
+  )
+)
+
+function dragStart(idx: number) {
+  dragIdx.value = idx
+}
+
+function dragOver(idx: number) {
+  if (dragIdx.value === null || dragIdx.value === idx) return
+  // Reorder store.backends (immutable swap)
+  const arr = [...store.backends]
+  const [moved] = arr.splice(dragIdx.value, 1)
+  arr.splice(idx, 0, moved)
+  store.backends = arr
+  // Update priorities
+  store.backends = store.backends.map((b, i) => ({ ...b, priority: i + 1 }))
+  dragIdx.value = idx
+}
+
+function drop() {
+  dragIdx.value = null
+}
+
+async function handleConfirmByok() {
+  await store.confirmByok()
+  byokConfirmed.value = false
+}
+
+onMounted(() => store.loadLlm())
+</script>
+
+<style scoped>
+.system-settings { max-width: 720px; margin: 0 auto; padding: var(--space-4, 24px); }
+h2 { font-size: 1.4rem; font-weight: 600; margin-bottom: 6px; color: var(--color-text-primary, #e2e8f0); }
+h3 { font-size: 1rem; font-weight: 600; margin-bottom: var(--space-3, 16px); color: var(--color-text-primary, #e2e8f0); }
+.tab-note { font-size: 0.82rem; color: var(--color-text-secondary, #94a3b8); margin-bottom: var(--space-6, 32px); }
+.form-section { margin-bottom: var(--space-8, 48px); padding-bottom: var(--space-6, 32px); border-bottom: 1px solid var(--color-border, rgba(255,255,255,0.08)); }
+.section-note { font-size: 0.78rem; color: var(--color-text-secondary, #94a3b8); margin-bottom: 14px; }
+.backend-list { display: flex; flex-direction: column; gap: 8px; margin-bottom: 20px; }
+.backend-card { display: flex; align-items: center; gap: 12px; padding: 10px 14px; background: var(--color-surface-2, rgba(255,255,255,0.04)); border: 1px solid var(--color-border, rgba(255,255,255,0.08)); border-radius: 8px; cursor: grab; user-select: none; }
+.backend-card:active { cursor: grabbing; }
+.drag-handle { font-size: 1.1rem; color: var(--color-text-secondary, #64748b); }
+.priority-badge { width: 22px; height: 22px; border-radius: 50%; background: rgba(124,58,237,0.2); color: var(--color-accent, #a78bfa); font-size: 0.72rem; font-weight: 700; display: flex; align-items: center; justify-content: center; flex-shrink: 0; }
+.backend-id { flex: 1; font-size: 0.9rem; font-family: monospace; color: var(--color-text-primary, #e2e8f0); }
+.toggle-label { display: flex; align-items: center; gap: 6px; cursor: pointer; font-size: 0.82rem; color: var(--color-text-secondary, #94a3b8); }
+.form-actions { display: flex; align-items: center; gap: var(--space-4, 24px); }
+.btn-primary { padding: 9px 24px; background: var(--color-accent, #7c3aed); color: #fff; border: none; border-radius: 7px; font-size: 0.9rem; cursor: pointer; font-weight: 600; }
+.btn-primary:disabled { opacity: 0.5; cursor: not-allowed; }
+.btn-cancel { padding: 9px 18px; background: transparent; border: 1px solid var(--color-border, rgba(255,255,255,0.2)); border-radius: 7px; color: var(--color-text-secondary, #94a3b8); cursor: pointer; font-size: 0.9rem; }
+.error-banner { background: rgba(239,68,68,0.1); border: 1px solid rgba(239,68,68,0.3); border-radius: 6px; color: #ef4444; padding: 10px 14px; margin-bottom: 20px; font-size: 0.85rem; }
+.error { color: #ef4444; font-size: 0.82rem; }
+/* BYOK Modal */
+.modal-overlay { position: fixed; inset: 0; background: rgba(0,0,0,0.6); display: flex; align-items: center; justify-content: center; z-index: 9999; }
+.modal-card { background: var(--color-surface-1, #1e293b); border: 1px solid var(--color-border, rgba(255,255,255,0.12)); border-radius: 12px; padding: 28px; max-width: 480px; width: 90%; }
+.modal-card h3 { font-size: 1.1rem; margin-bottom: 12px; color: var(--color-text-primary, #e2e8f0); }
+.modal-card p { font-size: 0.88rem; color: var(--color-text-secondary, #94a3b8); margin-bottom: 12px; }
+.modal-card ul { margin: 8px 0 16px 20px; font-size: 0.88rem; color: var(--color-text-primary, #e2e8f0); }
+.byok-warning { background: rgba(245,158,11,0.1); border: 1px solid rgba(245,158,11,0.3); border-radius: 6px; padding: 10px 12px; color: #fbbf24 !important; }
+.checkbox-row { display: flex; align-items: flex-start; gap: 8px; font-size: 0.85rem; color: var(--color-text-primary, #e2e8f0); cursor: pointer; margin: 16px 0; }
+.modal-actions { display: flex; gap: 10px; justify-content: flex-end; margin-top: 20px; }
+</style>