I guess it's playing word semantic. 100% of their MACHINES are running GO in SOME capacity, while other languages play some roles in other capacity.

I interpreted it as meaning that 100% of the code in the critical path is Go, while their greater application also includes some C code.

Like all those people that say they are running 100% python/php/ruby etc.

They've done studies. 65% of the time, it works every time.

the C code is also being run under Go's control via Cgo.

My production system is written in 100% bash and some other code run under Bash's control. :-)

if it was a 95/5% split, that might be a fair (and terrifying) thing to say.

Mine is running under 100% control of grub

grub doesn't control anything, it transfers control to the OS and is never contacted or heard from again. More concretely, in the case of Linux, the init task (first task and parent of every other task) function has a "tail" call to cpu_idle which never turns.

http://lxr.free-electrons.com/source/init/main.c?a=arm#L359