v7.53 increased the line length to 8kb, and 7.62 increased it again to 10kb. But there's always a website out there who can create longer string lengths between carriage returns.

I'm not sure how these lengths apply to extending the max for things like /sockread, so you'd have to test. As applied to %string the line length generally means 'characters' but to &binvar it often means 'bytes'. As long as the website has normal text there won't be a difference. But if there are characters above $chr(127) your &binvar can sometimes be unexpectedly shortchanged.

//var %string $str($chr(10004),6000) | bset -t &var 1 %string | echo -a $len($bvar(&var,1-).text) = 1/3rd *$maxlenl vs $len(%string)

You can now see the line length limit with $maxlenl, but you can't easily use lengths near that amount since that's the limit for the entire line, including commands, other parameters, and the %variable name itself.