diff --git a/web/src/api/chat.ts b/web/src/api/chat.ts
new file mode 100644
index 0000000..af9d108
--- /dev/null
+++ b/web/src/api/chat.ts
@@ -0,0 +1,167 @@
+import { request } from './client'
+
+export type MessageRole = 'user' | 'assistant'
+export type MessageStatus = 'pending' | 'ok' | 'error' | 'cancelled'
+export type TemplateScope = 'system' | 'user'
+
+export interface Conversation {
+  id: string
+  user_id: string
+  project_id?: string | null
+  workspace_id?: string | null
+  issue_id?: string | null
+  model_id: string
+  system_prompt: string
+  title?: string | null
+  title_generated_at?: string | null
+  created_at: string
+  updated_at: string
+}
+
+export interface Attachment {
+  id: string
+  filename: string
+  mime_type: string
+  size_bytes: number
+  sha256: string
+}
+
+export interface ChatMessage {
+  id: number
+  conversation_id: string
+  role: MessageRole
+  content: string
+  thinking?: string | null
+  status: MessageStatus
+  error_message?: string | null
+  prompt_tokens?: number | null
+  completion_tokens?: number | null
+  thinking_tokens?: number | null
+  attachments?: Attachment[]
+  created_at: string
+  updated_at: string
+}
+
+export interface PromptTemplate {
+  id: string
+  name: string
+  content: string
+  scope: TemplateScope
+  owner_id?: string | null
+  created_at: string
+  updated_at: string
+}
+
+export interface ConversationDetail {
+  conversation: Conversation
+  messages: ChatMessage[]
+}
+
+export interface SendMessageResp {
+  user_message_id: number
+  assistant_message_id: number
+  stream_url: string
+}
+
+export interface RetryMessageResp {
+  assistant_message_id: number
+  stream_url: string
+}
+
+export interface ListConversationsParams {
+  project_id?: string
+  workspace_id?: string
+  issue_id?: string
+  q?: string
+  limit?: number
+}
+
+export interface CreateConversationBody {
+  model_id: string
+  template_id?: string
+  system_prompt?: string
+  project_id?: string
+  workspace_id?: string
+  issue_id?: string
+}
+
+export interface UsageDailyItem {
+  day: string
+  prompt_tokens: number
+  completion_tokens: number
+  thinking_tokens: number
+  cost_usd: number
+}
+
+const enc = (v: string) => encodeURIComponent(v)
+
+function buildQuery(params: object): string {
+  const q = new URLSearchParams()
+  for (const [k, v] of Object.entries(params)) {
+    if (v === undefined || v === null || v === '') continue
+    q.set(k, String(v))
+  }
+  const s = q.toString()
+  return s ? '?' + s : ''
+}
+
+export const chatApi = {
+  // ===== Conversations =====
+  listConversations: (params: ListConversationsParams = {}) =>
+    request<{ items: Conversation[] }>(`/api/v1/conversations${buildQuery(params)}`).then(
+      (r) => r.items,
+    ),
+  createConversation: (body: CreateConversationBody) =>
+    request<Conversation>('/api/v1/conversations', { method: 'POST', body }),
+  getConversation: (id: string, opts: { before?: number; limit?: number } = {}) =>
+    request<ConversationDetail>(
+      `/api/v1/conversations/${enc(id)}${buildQuery({
+        before: opts.before,
+        limit: opts.limit ?? 50,
+      })}`,
+    ),
+  updateConversationTitle: (id: string, title: string) =>
+    request<void>(`/api/v1/conversations/${enc(id)}`, {
+      method: 'PATCH',
+      body: { title },
+    }),
+  deleteConversation: (id: string) =>
+    request<void>(`/api/v1/conversations/${enc(id)}`, { method: 'DELETE' }),
+
+  // ===== Messages =====
+  sendMessage: (
+    conversationId: string,
+    body: { content: string; attachment_ids?: string[] },
+  ) =>
+    request<SendMessageResp>(`/api/v1/conversations/${enc(conversationId)}/messages`, {
+      method: 'POST',
+      body,
+    }),
+  cancelMessage: (messageId: number) =>
+    request<void>(`/api/v1/messages/${messageId}/cancel`, { method: 'POST' }),
+  retryMessage: (messageId: number) =>
+    request<RetryMessageResp>(`/api/v1/messages/${messageId}/retry`, { method: 'POST' }),
+
+  // ===== Uploads =====
+  uploadAttachment: (file: File) => {
+    const fd = new FormData()
+    fd.append('file', file)
+    return request<Attachment>('/api/v1/uploads', { method: 'POST', body: fd })
+  },
+
+  // ===== Templates =====
+  listTemplates: () =>
+    request<{ items: PromptTemplate[] }>('/api/v1/prompt-templates').then((r) => r.items),
+  createTemplate: (body: { name: string; content: string; scope: TemplateScope }) =>
+    request<PromptTemplate>('/api/v1/prompt-templates', { method: 'POST', body }),
+  updateTemplate: (id: string, body: { name?: string; content?: string }) =>
+    request<void>(`/api/v1/prompt-templates/${enc(id)}`, { method: 'PATCH', body }),
+  deleteTemplate: (id: string) =>
+    request<void>(`/api/v1/prompt-templates/${enc(id)}`, { method: 'DELETE' }),
+
+  // ===== Personal usage =====
+  myDailyUsage: (from: string, to: string) =>
+    request<{ items: UsageDailyItem[] }>(
+      `/api/v1/users/me/usage${buildQuery({ from, to })}`,
+    ).then((r) => r.items),
+}
diff --git a/web/src/api/client.ts b/web/src/api/client.ts
index ee09b1b..bceee3f 100644
--- a/web/src/api/client.ts
+++ b/web/src/api/client.ts
@@ -21,10 +21,11 @@ export function configure(opts: {
 }
 
 export async function request<T>(path: string, opts: RequestOptions = {}): Promise<T> {
+  const isForm = opts.body instanceof FormData
   const headers: Record<string, string> = {
-    'Content-Type': 'application/json',
     'X-Client-Request-ID': crypto.randomUUID(),
   }
+  if (!isForm) headers['Content-Type'] = 'application/json'
   const token = authTokenProvider()
   if (token) headers['Authorization'] = `Bearer ${token}`
 
@@ -39,10 +40,16 @@ export async function request<T>(path: string, opts: RequestOptions = {}): Promi
   }
 
   try {
+    const body =
+      opts.body === undefined
+        ? undefined
+        : isForm
+          ? (opts.body as FormData)
+          : JSON.stringify(opts.body)
     const resp = await fetch(BASE + path, {
       method: opts.method || 'GET',
       headers,
-      body: opts.body !== undefined ? JSON.stringify(opts.body) : undefined,
+      body,
       signal: controller.signal,
     })
 
diff --git a/web/src/api/llmAdmin.ts b/web/src/api/llmAdmin.ts
new file mode 100644
index 0000000..56ffe15
--- /dev/null
+++ b/web/src/api/llmAdmin.ts
@@ -0,0 +1,122 @@
+import { request } from './client'
+
+export type LLMProvider = 'anthropic' | 'openai' | 'gemini'
+
+export interface LLMEndpoint {
+  id: string
+  provider: LLMProvider
+  display_name: string
+  base_url: string
+  created_at: string
+  updated_at: string
+}
+
+export interface ModelCapabilities {
+  image: boolean
+  pdf: boolean
+  audio: boolean
+  reasoning: boolean
+  tools: boolean
+}
+
+export interface LLMModel {
+  id: string
+  endpoint_id: string
+  model_id: string
+  display_name: string
+  capabilities: ModelCapabilities
+  context_window: number
+  max_output_tokens: number
+  prompt_price_per_million_usd: number
+  completion_price_per_million_usd: number
+  thinking_price_per_million_usd: number
+  is_title_generator: boolean
+  enabled: boolean
+  sort_order: number
+  created_at: string
+  updated_at: string
+}
+
+export interface CreateEndpointBody {
+  provider: LLMProvider
+  display_name: string
+  base_url: string
+  api_key: string
+}
+
+export interface UpdateEndpointBody {
+  display_name?: string
+  base_url?: string
+  api_key?: string
+}
+
+export interface CreateModelBody {
+  endpoint_id: string
+  model_id: string
+  display_name: string
+  capabilities?: Partial<ModelCapabilities>
+  context_window: number
+  max_output_tokens: number
+  prompt_price_per_million_usd?: number
+  completion_price_per_million_usd?: number
+  thinking_price_per_million_usd?: number
+  is_title_generator?: boolean
+  enabled?: boolean
+  sort_order?: number
+}
+
+export type UpdateModelBody = Partial<Omit<CreateModelBody, 'endpoint_id'>>
+
+export type AdminUsageGroupBy = 'user' | 'model' | 'day'
+
+export interface AdminUsageItem {
+  key: string
+  prompt_tokens: number
+  completion_tokens: number
+  thinking_tokens: number
+  cost_usd: number
+}
+
+const enc = (v: string) => encodeURIComponent(v)
+
+function buildQuery(params: object): string {
+  const q = new URLSearchParams()
+  for (const [k, v] of Object.entries(params)) {
+    if (v === undefined || v === null || v === '') continue
+    q.set(k, String(v))
+  }
+  const s = q.toString()
+  return s ? '?' + s : ''
+}
+
+export const llmAdminApi = {
+  // ===== Endpoints =====
+  listEndpoints: () =>
+    request<{ items: LLMEndpoint[] }>('/api/v1/admin/llm-endpoints').then((r) => r.items),
+  createEndpoint: (body: CreateEndpointBody) =>
+    request<LLMEndpoint>('/api/v1/admin/llm-endpoints', { method: 'POST', body }),
+  updateEndpoint: (id: string, body: UpdateEndpointBody) =>
+    request<void>(`/api/v1/admin/llm-endpoints/${enc(id)}`, { method: 'PATCH', body }),
+  deleteEndpoint: (id: string) =>
+    request<void>(`/api/v1/admin/llm-endpoints/${enc(id)}`, { method: 'DELETE' }),
+  testEndpoint: (id: string) =>
+    request<void>(`/api/v1/admin/llm-endpoints/${enc(id)}/test`, { method: 'POST' }),
+
+  // ===== Models =====
+  listModels: (onlyEnabled = false) =>
+    request<{ items: LLMModel[] }>(
+      `/api/v1/admin/llm-models${buildQuery({ only_enabled: onlyEnabled })}`,
+    ).then((r) => r.items),
+  createModel: (body: CreateModelBody) =>
+    request<LLMModel>('/api/v1/admin/llm-models', { method: 'POST', body }),
+  updateModel: (id: string, body: UpdateModelBody) =>
+    request<void>(`/api/v1/admin/llm-models/${enc(id)}`, { method: 'PATCH', body }),
+  deleteModel: (id: string) =>
+    request<void>(`/api/v1/admin/llm-models/${enc(id)}`, { method: 'DELETE' }),
+
+  // ===== Usage =====
+  adminUsage: (from: string, to: string, groupBy: AdminUsageGroupBy) =>
+    request<{ items: AdminUsageItem[] }>(
+      `/api/v1/admin/usage${buildQuery({ from, to, group_by: groupBy })}`,
+    ),
+}