The other day while looking around for stuff about the RT-AX5400 routers I recently bought (one for work, one for home), I stumbled across https://www.asus.com/us/support/faq/1051929/ dated May 7, 2024.
Unfortunately, the only one with "4 years (until 31th December 2028)" is the RT-BE88U which I couldn't find in the US. It seems to have just been announced on March 27, 2024: https://press.asus.com/news/asus-unveils-rt-be88u-wifi-7-dual-band-router/.
The dates there probably don't spell the end of security updates for those routers, but I can only assume that Asus is (legally?) obligated in the UK to provide security updates for those routers until at least those dates...
Unfortunately, the only one with "4 years (until 31th December 2028)" is the RT-BE88U which I couldn't find in the US. It seems to have just been announced on March 27, 2024: https://press.asus.com/news/asus-unveils-rt-be88u-wifi-7-dual-band-router/.
The dates there probably don't spell the end of security updates for those routers, but I can only assume that Asus is (legally?) obligated in the UK to provide security updates for those routers until at least those dates...