diff --git a/apps/dashboard/src/features/conversations/conversation-detail.tsx b/apps/dashboard/src/features/conversations/conversation-detail.tsx
index d3011eb..2bfffda 100644
--- a/apps/dashboard/src/features/conversations/conversation-detail.tsx
+++ b/apps/dashboard/src/features/conversations/conversation-detail.tsx
@@ -32,6 +32,7 @@ function MessageHistory({ conversation }: { conversation: ConversationDetailResp
             <strong>{message.isSelf
               ? `You${conversation.owner ? ` (u/${conversation.owner.redditUsername})` : ''}`
               : <RedditUsernameLink username={conversation.username} />}</strong>
+            {message.isAi ? <span aria-label="Sent by AI" className="conversation-ai-badge">AI</span> : null}
             <time dateTime={new Date(message.timestamp).toISOString()}>{formatMessageTime(message.timestamp)}</time>
           </div>
           <p>{message.text}</p>
diff --git a/apps/dashboard/src/features/conversations/conversations.css b/apps/dashboard/src/features/conversations/conversations.css
index 718798d..f0e2946 100644
--- a/apps/dashboard/src/features/conversations/conversations.css
+++ b/apps/dashboard/src/features/conversations/conversations.css
@@ -123,3 +123,17 @@
     text-align: left;
   }
 }
+.conversation-ai-badge {
+  display: inline-flex;
+  align-items: center;
+  min-height: 1.25rem;
+  padding: 0.125rem 0.4rem;
+  border: 1px solid rgba(99, 102, 241, 0.35);
+  border-radius: 999px;
+  background: rgba(99, 102, 241, 0.12);
+  color: #5558c9;
+  font-size: 0.6875rem;
+  font-weight: 700;
+  letter-spacing: 0.06em;
+  line-height: 1;
+}
diff --git a/packages/api-contracts/src/chats.ts b/packages/api-contracts/src/chats.ts
index 0be6ebd..22f4065 100644
--- a/packages/api-contracts/src/chats.ts
+++ b/packages/api-contracts/src/chats.ts
@@ -13,6 +13,7 @@ export const ChatMessageSchema = z.strictObject({
   text: z.string(),
   timestamp: z.number(),
   isSelf: z.boolean(),
+  isAi: z.boolean().optional(),
   media: z.array(ChatMediaSchema).optional(),
 });
 export const ActiveChatSchema = z.strictObject({
diff --git a/src/services/conversation-automation.ts b/src/services/conversation-automation.ts
index 6c2bc7b..2a142d3 100644
--- a/src/services/conversation-automation.ts
+++ b/src/services/conversation-automation.ts
@@ -7,6 +7,7 @@ import type { ChatService } from './chat/service.js';
 import {
   buildConversationState,
   chooseConversationIntent,
+  conversationMessageFingerprint,
   MAX_AUTOMATED_CONVERSATION_TURNS,
   mergeConversationState,
   remainingAutomationTurns,
@@ -101,6 +102,7 @@ export class ConversationAutomationService {
     state.askedForMedia = true;
     state.automation.turnsUsed += 1;
     state.automation.lastIncomingKey = incomingKey;
+    state.automation.aiMessageFingerprints.push(conversationMessageFingerprint(reply));
     const exhausted = state.automation.turnsUsed >= MAX_AUTOMATED_CONVERSATION_TURNS;
     if (exhausted) {
       state.automation.status = 'human-required';
diff --git a/src/services/conversation-state.ts b/src/services/conversation-state.ts
index ea1e6a3..f377195 100644
--- a/src/services/conversation-state.ts
+++ b/src/services/conversation-state.ts
@@ -1,3 +1,5 @@
+import { createHash } from 'node:crypto';
+
 export interface ConversationMessage {
   sender: string;
   text: string;
@@ -45,6 +47,8 @@ export interface ConversationAutomationState {
   status: ConversationAutomationStatus;
   lastIncomingKey: string | null;
   handoffReason: string | null;
+  /** SHA-256 fingerprints avoid storing a second copy of generated message text. */
+  aiMessageFingerprints: string[];
 }
 
 export function createConversationAutomationState(): ConversationAutomationState {
@@ -53,9 +57,14 @@ export function createConversationAutomationState(): ConversationAutomationState
     status: 'active',
     lastIncomingKey: null,
     handoffReason: null,
+    aiMessageFingerprints: [],
   };
 }
 
+export function conversationMessageFingerprint(message: string): string {
+  return createHash('sha256').update(message.trim()).digest('hex');
+}
+
 export function remainingAutomationTurns(state: ConversationState): number {
   if (state.automation.status !== 'active') return 0;
   return Math.max(0, MAX_AUTOMATED_CONVERSATION_TURNS - state.automation.turnsUsed);
@@ -222,6 +231,9 @@ function parseAutomationState(value: unknown): ConversationAutomationState {
     status,
     lastIncomingKey: typeof parsed.lastIncomingKey === 'string' ? parsed.lastIncomingKey : null,
     handoffReason: typeof parsed.handoffReason === 'string' ? parsed.handoffReason : null,
+    aiMessageFingerprints: Array.isArray(parsed.aiMessageFingerprints)
+      ? parsed.aiMessageFingerprints.filter((item): item is string => typeof item === 'string')
+      : [],
   };
 }
 
diff --git a/src/web/routes/conversations.ts b/src/web/routes/conversations.ts
index a7ffd58..28fe9f8 100644
--- a/src/web/routes/conversations.ts
+++ b/src/web/routes/conversations.ts
@@ -4,6 +4,7 @@ import type { WebContext } from '../context.js';
 import {
   buildConversationState,
   chooseConversationIntent,
+  conversationMessageFingerprint,
   mergeConversationState,
   remainingAutomationTurns,
 } from '../../services/conversation-state.js';
@@ -169,12 +170,14 @@ export function createConversationsRouter(ctx: WebContext): Router {
         imageUrl: string | null;
         sentAt: number;
       } | null = null;
+      let automatedOpener: string | null = null;
       try {
         const messagesRepo = resolved.runtime?.resources.messagesRepo ?? ctx.repos.messages;
         const sent = conversation.roomId
           ? messagesRepo.getByChatRoomId(conversation.roomId)
             ?? messagesRepo.getLatestByRecipient(conversation.username)
           : messagesRepo.getLatestByRecipient(conversation.username);
+        automatedOpener = sent?.message ?? null;
         if (sent && sent.postId) {
           const url = sent.postUrl ?? (sent.subreddit
             ? `https://www.reddit.com/r/${sent.subreddit}/comments/${sent.postId}/`
@@ -205,9 +208,25 @@ export function createConversationsRouter(ctx: WebContext): Router {
         intelligence.state.automation.handoffReason = intelligence.state.boundaries.join('; ');
       }
       if (conversation.roomId) stateRepo?.save(conversation.roomId, intelligence.state);
+      const aiFingerprints = new Map<string, number>();
+      if (automatedOpener) {
+        aiFingerprints.set(conversationMessageFingerprint(automatedOpener), 1);
+      }
+      for (const fingerprint of intelligence.state.automation.aiMessageFingerprints) {
+        aiFingerprints.set(fingerprint, (aiFingerprints.get(fingerprint) ?? 0) + 1);
+      }
+      const annotatedMessages = conversation.messages?.map((message) => {
+        if (!message.isSelf) return message;
+        const fingerprint = conversationMessageFingerprint(message.text);
+        const remainingMatches = aiFingerprints.get(fingerprint) ?? 0;
+        if (remainingMatches === 0) return message;
+        aiFingerprints.set(fingerprint, remainingMatches - 1);
+        return { ...message, isAi: true };
+      });
 
       res.json({
         ...conversation,
+        ...(annotatedMessages ? { messages: annotatedMessages } : {}),
         owner: resolved.runtime
           ? { accountId: resolved.runtime.session.accountId, redditUsername: resolved.runtime.session.redditUsername }
           : currentOwner(),
diff --git a/tests/conversation-automation.test.ts b/tests/conversation-automation.test.ts
index 8a1ea6a..30cb23e 100644
--- a/tests/conversation-automation.test.ts
+++ b/tests/conversation-automation.test.ts
@@ -46,6 +46,7 @@ describe('conversation automation', () => {
     expect(third).toMatchObject({ kind: 'human-required', remainingTurns: 0 });
     expect(chat.sendChatMessage).toHaveBeenCalledTimes(3);
     expect(getSaved()?.automation).toMatchObject({ turnsUsed: 3, status: 'human-required' });
+    expect(getSaved()?.automation.aiMessageFingerprints).toHaveLength(3);
     expect(await service.processConversation(incoming(3))).toBeNull();
   });
 
diff --git a/tests/dashboard/conversations.test.tsx b/tests/dashboard/conversations.test.tsx
index cc77808..e204f5e 100644
--- a/tests/dashboard/conversations.test.tsx
+++ b/tests/dashboard/conversations.test.tsx
@@ -40,7 +40,7 @@ function detailFixture(chat = alice) {
   return {
     ...chat,
     messages: [
-      { sender: 'me', text: 'Hello Alice', timestamp: 1_785_999_900_000, isSelf: true },
+      { sender: 'me', text: 'Hello Alice', timestamp: 1_785_999_900_000, isSelf: true, isAi: true },
       { sender: 'alice', text: 'Good to hear from you', timestamp: 1_786_000_000_000, isSelf: false },
     ],
     triggeringPost: {
@@ -136,6 +136,7 @@ describe('ConversationsPage', () => {
       expect(profileLink).toHaveAttribute('href', 'https://www.reddit.com/u/alice');
     }
     expect(screen.getByText('Good to hear from you')).toBeInTheDocument();
+    expect(screen.getByLabelText('Sent by AI')).toHaveTextContent('AI');
     expect(screen.getByRole('link', { name: 'Looking for a chat' })).toHaveAttribute('href', expect.stringContaining('post-1'));
     expect(screen.getByRole('img', { name: 'Source post: Looking for a chat' })).toHaveAttribute(
       'src',
diff --git a/tests/openrouter-client.test.ts b/tests/openrouter-client.test.ts
index 4176db7..c11cfe4 100644
--- a/tests/openrouter-client.test.ts
+++ b/tests/openrouter-client.test.ts
@@ -574,7 +574,7 @@ describe('OpenRouterClient', () => {
           boundaries: [],
           askedForMedia: false,
           topics: [],
-          automation: { turnsUsed: 0, status: 'active', lastIncomingKey: null, handoffReason: null },
+          automation: { turnsUsed: 0, status: 'active', lastIncomingKey: null, handoffReason: null, aiMessageFingerprints: [] },
         },
         { kind: 'answer-question', reason: 'their latest message asks a direct question' },
       );
diff --git a/tests/web/conversations-route.test.ts b/tests/web/conversations-route.test.ts
index 98aed96..b9ae6b7 100644
--- a/tests/web/conversations-route.test.ts
+++ b/tests/web/conversations-route.test.ts
@@ -3,6 +3,7 @@ import type { AddressInfo } from 'node:net';
 import { afterEach, describe, expect, it, vi } from 'vitest';
 import type { WebContext } from '../../src/web/context.js';
 import { createConversationsRouter } from '../../src/web/routes/conversations.js';
+import { buildConversationState, conversationMessageFingerprint } from '../../src/services/conversation-state.js';
 
 const servers: Array<ReturnType<express.Express['listen']>> = [];
 
@@ -234,13 +235,14 @@ describe('conversations route', () => {
       lastMessageSnippet: 'Hello',
       isFromUs: false,
       unread: false,
-      messages: [{
-        sender: 'alice',
-        text: 'Hello',
-        timestamp: 1_786_000_000_000,
-        isSelf: false,
-      }],
+      messages: [
+        { sender: 'me', text: 'Automated hello', timestamp: 1_785_999_900_000, isSelf: true },
+        { sender: 'alice', text: 'Hello', timestamp: 1_786_000_000_000, isSelf: false },
+      ],
     };
+    const savedState = buildConversationState(conversation.messages);
+    savedState.automation.turnsUsed = 1;
+    savedState.automation.aiMessageFingerprints = [conversationMessageFingerprint('Automated hello')];
     const refreshTopChats = vi.fn();
     const loadConversationDetails = vi.fn();
     const context = {
@@ -249,6 +251,7 @@ describe('conversations route', () => {
         messages: { getLatestByRecipient: vi.fn().mockReturnValue(undefined) },
       },
       services: {
+        conversationState: { get: vi.fn().mockReturnValue(savedState), save: vi.fn() },
         chat: {
           getSyncStatus: vi.fn().mockReturnValue({
             syncing: false,
@@ -270,11 +273,13 @@ describe('conversations route', () => {
     const body = await response.json();
     expect(body.username).toBe('alice');
     expect(body.automation).toEqual({
-      turnsUsed: 0,
-      remainingTurns: 3,
+      turnsUsed: 1,
+      remainingTurns: 2,
       status: 'active',
       handoffReason: null,
     });
+    expect(body.messages[0]).toMatchObject({ text: 'Automated hello', isAi: true });
+    expect(body.messages[1].isAi).toBeUndefined();
     expect(refreshTopChats).not.toHaveBeenCalled();
     expect(loadConversationDetails).not.toHaveBeenCalled();
   });
@@ -310,10 +315,12 @@ describe('conversations route', () => {
     const response = await request(app, '/api/conversations/room-alice');
 
     expect(response.status).toBe(200);
-    expect((await response.json()).triggeringPost).toEqual({
+    const body = await response.json();
+    expect(body.triggeringPost).toEqual({
       id: 'post-exact', subreddit: 'example', title: 'Exact source post',
       url: roomOrigin.postUrl, imageUrl: roomOrigin.postImageUrl, sentAt: 9,
     });
+    expect(body.messages[0]).toMatchObject({ text: 'Hello', isAi: true });
     expect(context.repos.messages.getLatestByRecipient).not.toHaveBeenCalled();
   });