Just like the old userfriendly.org comic, where marketing promises nine fives instead of five nines.

https://web.archive.org/web/20220226060634/http://ars.userfr...

https://web.archive.org/web/20220226061736/http://ars.userfr...

Nah, they are referring to the system prompt that runs Claude: "Always underpromise and overdeliver. Make no mistakes."