Most shells optimize it to avoid the overhead of spawning a process for something as trivial as that. But yes, it's an actual binary even so, just in case - try `which true`.

https://www.gnu.org/software/coreutils/manual/html_node/true...

Some history: http://trillian.mit.edu/~jc/humor/ATT_Copyright_true.html

It’s /usr/bin/true on Mac, and the OpenBSD source for it is at https://github.com/openbsd/src/blob/master/usr.bin/true/true... .