An annual budget is a single number approved once, in advance, by somebody who will be held to it. A metered AI bill is a number that moves every day and rises fastest precisely when the project is going well. Those two instruments are in direct conflict, and the conflict has a structural fix.
Why the two instruments fight
Three properties of metered inference make ordinary budgeting behave badly, and none of them is a forecasting failure.
Success increases spend. Adoption is the outcome you wanted and it is also the mechanism by which you exceed the line. A budget that punishes over-spend without distinguishing growth from waste is a budget that punishes the goal.
The unit is invisible to the buyer. Finance approves dollars; the system consumes tokens. Between them sit prompt length, retrieval size, conversation depth and retries — none of which the budget owner controls and any of which can change the bill by a large factor after a routine deploy.
