https://pike.lysator.liu.se/generated/manual/modref/ex/predef_3A_3A/strlen.html says that strlen is deprecated and that we are supposed to use sizeof instead. At the same time, I see new Pike code beeing committed that use strlen (282a8a93 by Grubba 2018-01-04, a5c5c7cd by Bill 2017-12-22, be932f508271a by Arne 2017-10-31, 26da463c by Martin 2017-02-21, ff2876e2cb by Grubba 2017-01-30) (in some cases this is just an strlen that is moved, but still).
To be fair, there is also some new code that uses sizeof(string). I get why strlen(multiset|array|mapping|object thing) is deprecated, but peronally I'd like to keep strlen(string) as a supported function. I think it sometimes produces more readable code.