diff --git a/api/comms/chat.go b/api/comms/chat.go
index 67202ce7..71d96d47 100644
--- a/api/comms/chat.go
+++ b/api/comms/chat.go
@@ -217,6 +217,21 @@ func chatReadMessages(db dbv1.DBTX, ctx context.Context, userId int32, chatId st
 	return err
 }
 
+// chatReadAllMessages clears unread state for every chat this user belongs to.
+// The (last_active_at IS NULL OR last_active_at < $1) guard mirrors the
+// per-chat chat.read handler so out-of-order RPCs can't roll back a more
+// recent read. The unread_count > 0 filter keeps the write set small.
+func chatReadAllMessages(db dbv1.DBTX, ctx context.Context, userId int32, readTimestamp time.Time) error {
+	_, err := db.Exec(ctx, `
+		update chat_member
+		set unread_count = 0, last_active_at = $1
+		where user_id = $2
+		  and (last_active_at is null or last_active_at < $1)
+		  and unread_count > 0`,
+		readTimestamp.UTC(), userId)
+	return err
+}
+
 var permissions = []ChatPermission{
 	ChatPermissionFollowees,
 	ChatPermissionFollowers,
diff --git a/api/comms/chat_test.go b/api/comms/chat_test.go
index 53a141ac..44e12d3c 100644
--- a/api/comms/chat_test.go
+++ b/api/comms/chat_test.go
@@ -139,3 +139,68 @@ func TestChat(t *testing.T) {
 
 	assertReaction(user1Id, replyMessageId, nil)
 }
+
+func TestChatReadAllMessages(t *testing.T) {
+	pool := database.CreateTestDatabase(t, "test_comms")
+	defer pool.Close()
+
+	ctx := context.Background()
+	seededRand := rand.New(rand.NewSource(time.Now().UnixNano()))
+
+	user1Id := int32(1)
+	user2Id := int32(2)
+	user3Id := int32(3)
+
+	chatA := trashid.ChatID(int(user1Id), int(user2Id))
+	chatB := trashid.ChatID(int(user1Id), int(user3Id))
+	SetupChatWithMembers(t, pool, ctx, chatA, user1Id, user2Id, "a1", "a2")
+	SetupChatWithMembers(t, pool, ctx, chatB, user1Id, user3Id, "b1", "b3")
+
+	assertUnreadCount := func(chatId string, userId int32, expected int) {
+		t.Helper()
+		unreadCount := 0
+		err := pool.QueryRow(ctx, "select unread_count from chat_member where chat_id = $1 and user_id = $2", chatId, userId).Scan(&unreadCount)
+		assert.NoError(t, err)
+		assert.Equal(t, expected, unreadCount, "unread for chat %s user %d", chatId, userId)
+	}
+
+	// Send user1Id one message in each chat from the other party.
+	err := chatSendMessage(pool, ctx, user2Id, chatA, strconv.Itoa(seededRand.Int()), time.Now(), "hi from 2")
+	assert.NoError(t, err)
+	err = chatSendMessage(pool, ctx, user3Id, chatB, strconv.Itoa(seededRand.Int()), time.Now(), "hi from 3")
+	assert.NoError(t, err)
+
+	assertUnreadCount(chatA, user1Id, 1)
+	assertUnreadCount(chatB, user1Id, 1)
+	// Senders' own unread counts stay at zero.
+	assertUnreadCount(chatA, user2Id, 0)
+	assertUnreadCount(chatB, user3Id, 0)
+
+	// Single call clears every unread chat for user1Id without touching
+	// the other members' chats.
+	readTs := time.Now()
+	err = chatReadAllMessages(pool, ctx, user1Id, readTs)
+	assert.NoError(t, err)
+
+	assertUnreadCount(chatA, user1Id, 0)
+	assertUnreadCount(chatB, user1Id, 0)
+
+	// Re-confirm: a stale read (older timestamp) does NOT roll back.
+	// Add a new unread, advance via chatReadAllMessages, then try a stale read.
+	err = chatSendMessage(pool, ctx, user2Id, chatA, strconv.Itoa(seededRand.Int()), time.Now(), "another from 2")
+	assert.NoError(t, err)
+	assertUnreadCount(chatA, user1Id, 1)
+
+	freshTs := time.Now()
+	err = chatReadAllMessages(pool, ctx, user1Id, freshTs)
+	assert.NoError(t, err)
+	assertUnreadCount(chatA, user1Id, 0)
+
+	// Older timestamp must be a no-op for last_active_at.
+	err = chatReadAllMessages(pool, ctx, user1Id, freshTs.Add(-time.Hour))
+	assert.NoError(t, err)
+	var lastActive time.Time
+	err = pool.QueryRow(ctx, "select last_active_at from chat_member where chat_id = $1 and user_id = $2", chatA, user1Id).Scan(&lastActive)
+	assert.NoError(t, err)
+	assert.WithinDuration(t, freshTs.UTC(), lastActive.UTC(), time.Second, "stale read should not roll back last_active_at")
+}
diff --git a/api/comms/rpc_processor.go b/api/comms/rpc_processor.go
index c3d4c11f..c05268bb 100644
--- a/api/comms/rpc_processor.go
+++ b/api/comms/rpc_processor.go
@@ -270,6 +270,13 @@ select last_active_at from chat_member where chat_id = $1 and user_id = $2`
 					return err
 				}
 			}
+		case RPCMethodChatReadAll:
+			// No params to unmarshal. The per-row last_active_at guard lives
+			// inside chatReadAllMessages so we don't have to read first.
+			err = chatReadAllMessages(tx, ctx, userId, messageTs)
+			if err != nil {
+				return err
+			}
 		case RPCMethodChatPermit:
 			var params ChatPermitRPCParams
 			err = json.Unmarshal(rawRpc.Params, &params)
diff --git a/api/comms/schema.go b/api/comms/schema.go
index 3aac7523..1d527512 100644
--- a/api/comms/schema.go
+++ b/api/comms/schema.go
@@ -95,6 +95,13 @@ type ChatReadRPCParams struct {
 	ChatID string `json:"chat_id"`
 }
 
+type ChatReadAllRPC struct {
+	Method ChatReadAllRPCMethod `json:"method"`
+	Params ChatReadAllRPCParams `json:"params"`
+}
+
+type ChatReadAllRPCParams struct{}
+
 type ChatBlockRPC struct {
 	Method ChatBlockRPCMethod `json:"method"`
 	Params ChatBlockRPCParams `json:"params"`
@@ -367,6 +374,12 @@ const (
 	MethodChatRead ChatReadRPCMethod = "chat.read"
 )
 
+type ChatReadAllRPCMethod string
+
+const (
+	MethodChatReadAll ChatReadAllRPCMethod = "chat.read_all"
+)
+
 type ChatBlockRPCMethod string
 
 const (
@@ -410,6 +423,7 @@ const (
 	RPCMethodChatPermit          RPCMethod = "chat.permit"
 	RPCMethodChatReact           RPCMethod = "chat.react"
 	RPCMethodChatRead            RPCMethod = "chat.read"
+	RPCMethodChatReadAll         RPCMethod = "chat.read_all"
 	RPCMethodChatUnblock         RPCMethod = "chat.unblock"
 	RPCMethodUserValidateCanChat RPCMethod = "user.validate_can_chat"
 )
diff --git a/api/comms/validator.go b/api/comms/validator.go
index d425d517..1d2948d5 100644
--- a/api/comms/validator.go
+++ b/api/comms/validator.go
@@ -67,6 +67,9 @@ func (vtor *Validator) Validate(ctx context.Context, userId int32, rawRpc RawRPC
 		return vtor.validateChatReact(vtor.pool, ctx, userId, rawRpc)
 	case RPCMethodChatRead:
 		return vtor.validateChatRead(userId, rawRpc)
+	case RPCMethodChatReadAll:
+		// No params to validate; ban check above already gates this call.
+		return nil
 	case RPCMethodChatPermit:
 		return vtor.validateChatPermit(userId, rawRpc)
 	case RPCMethodChatBlock: