Many of these devices have custom ISP firmware that prevents users from manually flashing generic or "international" versions.
This is the ultimate fix for poor performance. Instead of hunting for hacked firmware to make the F670L perform better, ask your ISP to put the device into "Bridge Mode." This turns the ZTE into a simple fiber modem, passing the raw internet connection to a high-performance router of your choice (like an ASUS or TP-Link Omada system). You get better Wi-Fi, better features, and you don't risk destroying your ONT. zte zxhn f670l firmware download hot extra quality
: Always back up your current configuration before attempting an upgrade to ensure you can restore your settings if the process is interrupted. Many of these devices have custom ISP firmware