Because ZTE does not provide public direct download links for consumer ONTs on their main site, use these official and secondary methods: Support - ZTE-Server And Storage
The latest official firmware for the is typically managed and pushed automatically by your Internet Service Provider (ISP) because it is a GPON ONT (Optical Network Terminal). Official Download Sources zte f670l latest firmware download
Disable routing functions on the F670L and use your own router (Asus, TP-Link, MikroTik) for updates and better security. To do this: Because ZTE does not provide public direct download