Depending on the download portal, the K2's current available is v3.4.99 but I've seen 3.4.104 on the Hikvision FTP server. I've loaded v4.21.00 on my test K2 and it's stable. It's available from the EU portal for the 7700 I series. Keep in mind there may be risks using firmware designed for a different series including voiding your warranty.