CIMChat::getChatActiveUserCount

private function getChatActiveUserCount($chatId): int
{
	$chatUserCount = IMModelRelationTable::getList(
		[
			'select' => ['CNT', 'CHAT_ID'],
			'filter' => [
				['=CHAT_ID' => $chatId],
				['=USER.ACTIVE' => 'Y']
			],
			'runtime' => [
				new BitrixMainEntityExpressionField('CNT', 'COUNT(*)')
			]
		]
	)->fetch();

	return (int)$chatUserCount['CNT'];
}