Missing AI agent cost data is not zero
My agent spend ledger showed $0 for the day. The agents had run all morning. The number was a lie, and the bug behind it is one almost every cost tracker ships with.
Short version: when a provider's billing data has not arrived yet, a naive cost tracker records $0 for that period. For AI agents that run unattended, this hides the exact spending you built the tracker to catch. The fix is to model missing data as a distinct "unknown" state, never as zero, so a day you cannot measure reads as unmeasured instead of free.
Why a $0 day is the dangerous one
I run a fleet of scheduled agents. They digest articles, review drafts, sweep a queue overnight. Real model calls, real dollars. I built a daily spend ledger to answer one question every morning: what did yesterday cost, and am I about to blow the budget?
