diff --git a/apps/chat/src/chat.app.ts b/apps/chat/src/chat.app.ts
index b5fb63a..97afbbb 100644
--- a/apps/chat/src/chat.app.ts
+++ b/apps/chat/src/chat.app.ts
@@ -127,7 +127,12 @@ async function sendToThread(c: Context<App>) {
 		contents === undefined || contents === ''
 			? null
 			: await postMessage(c.env.DB, { chatThreadId, senderPlayerId: id, contents })
-	if (posted !== null) await pushChatMessage(c, posted)
+	if (posted !== null) {
+		await pushChatMessage(c, posted)
+		// Sending is reading: the reference answers with `lastReadMessageId` already at the
+		// message just posted, so the sender's own thread doesn't come back unread.
+		await markThreadRead(c.env.DB, chatThreadId, id, posted.chatMessageId)
+	}
 
 	const thread = await threadWithMessages(c, chatThreadId, id, DEFAULT_THREAD_MESSAGE_COUNT)
 	return c.json({
@@ -261,7 +266,10 @@ const app = new Hono<App>()
 			contents === undefined || contents === ''
 				? null
 				: await postMessage(c.env.DB, { chatThreadId, senderPlayerId: id, contents })
-		if (posted !== null) await pushChatMessage(c, posted)
+		if (posted !== null) {
+			await pushChatMessage(c, posted)
+			await markThreadRead(c.env.DB, chatThreadId, id, posted.chatMessageId)
+		}
 
 		const thread = await getThreadForPlayer(c.env.DB, chatThreadId, id)
 		if (thread === null) throw new Error(`thread ${chatThreadId} vanished after creation`)
diff --git a/apps/chat/src/test/integration/api.test.ts b/apps/chat/src/test/integration/api.test.ts
index 34ea7c6..5df39bb 100644
--- a/apps/chat/src/test/integration/api.test.ts
+++ b/apps/chat/src/test/integration/api.test.ts
@@ -102,6 +102,7 @@ describe('chat endpoints', () => {
 				playerIds: [player, 881002],
 				lastReadMessageId: 0,
 				chatThreadName: '',
+				chatThreadType: 0,
 				snoozedUntil: null,
 				isFavorited: false,
 			},
@@ -249,6 +250,7 @@ describe('thread storage', () => {
 			playerIds: [9489959, VIEWER],
 			lastReadMessageId: latest.chatMessageId,
 			chatThreadName: '',
+			chatThreadType: 0,
 			snoozedUntil: null,
 			isFavorited: false,
 		})
@@ -939,7 +941,13 @@ describe('POST /thread/:id', () => {
 
 		const body = (await res.json()) as {
 			chatResult: number
-			chatThread: { chatThreadId: number; playerIds: number[]; messages: ChatMessage[] }
+			chatThread: {
+				chatThreadId: number
+				playerIds: number[]
+				lastReadMessageId: number
+				chatThreadType: number
+				messages: ChatMessage[]
+			}
 		}
 		expect(body.chatResult).toBe(0)
 
@@ -955,6 +963,9 @@ describe('POST /thread/:id', () => {
 		})
 		expect(body.chatThread.messages[1]).toMatchObject({ senderPlayerId: SYSTEM_SENDER_ID })
 
+		// Sending marks the thread read for the sender, so it doesn't come back unread.
+		expect(body.chatThread.lastReadMessageId).toBe(body.chatThread.messages[0]!.chatMessageId)
+
 		// And it's stored, not just echoed.
 		expect(await getThreadMessages(env.DB, chatThreadId)).toEqual(body.chatThread.messages)
 	})
diff --git a/apps/chat/src/thread-db.ts b/apps/chat/src/thread-db.ts
index 84e49ee..1bbe0f0 100644
--- a/apps/chat/src/thread-db.ts
+++ b/apps/chat/src/thread-db.ts
@@ -69,10 +69,20 @@ export interface ChatThread {
 	 * GetChatBetweenPlayers) and falls back to naming the members when it's blank.
 	 */
 	chatThreadName: string
+	/**
+	 * Which kind of conversation this is. Every thread the reference serves here comes back
+	 * as 0, and nothing in the worker distinguishes DMs from groups, so it's a constant —
+	 * but the field itself has to be present: the client deserializes it as a non-nullable
+	 * int and drops the whole response when it's missing.
+	 */
+	chatThreadType: number
 	snoozedUntil: string | null
 	isFavorited: boolean
 }
 
+/** The only thread type the reference ever serves. See `ChatThread.chatThreadType`. */
+const CHAT_THREAD_TYPE_DEFAULT = 0
+
 /** The joined row backing a rendered thread, before it's shaped for the client. */
 interface ThreadRow {
 	chat_thread_id: number
@@ -109,6 +119,7 @@ function toThread(row: ThreadRow): ChatThread {
 		lastReadMessageId: row.last_read_message_id ?? 0,
 		// Null in the column means "unnamed"; the client dereferences it unchecked.
 		chatThreadName: row.chat_thread_name ?? '',
+		chatThreadType: CHAT_THREAD_TYPE_DEFAULT,
 		snoozedUntil: row.snoozed_until,
 		isFavorited: row.is_favorited !== 0,
 	}