Well, looking into the sources of the coreutils tools, true is one of the smallest. It is smaller than kill, though larger than false which is the very smallest:

$ for i in src/*c; do wc -l $i; done | sort -nr | tail -11

78 src/true.c

74 src/operand2sig.c

73 src/sync.c

37 src/prog-fprintf.c

2 src/uname-uname.c

2 src/uname-arch.c

2 src/ls-vdir.c

2 src/ls-ls.c

2 src/ls-dir.c

2 src/lbracket.c

2 src/false.c

So, true has 78 lines, but only 58 of them are actually code (the rest are blank lines and comments):

$ grep . src/true.c | awk '{ if(//*/){a=0} if(a){print} if(/*//){a=1}}' | wc

50

And yes, a lot of that (10 lines) are dedicated to the usage function. The program is still tiny though.

Also, the reason that false is tinier is that it simply calls true:

$ cat src/false.c

#define EXIT_STATUS EXIT_FAILURE

#include "true.c"