I worked on ad systems at Facebook, and yes it's (approximately) true for those as well. The thing to realize that "in production" almost never means "rolled o

I worked on ad systems at Facebook, and yes it's (approximately) true for those as well. The thing to realize that "in production" almost never means "rolled out to 100% of users from 0%". Instead you'd do very slow rollouts to, say, 1% of people in Hungary (or whatever) and use a ton of automatic measurements over time as well as lots and lots of tests to validate that things were working as expected before rolling out a little more, then a little more after that. By the time the code is actually being hit by the majority of users, it's often been run billions of times already.