# Cost and usage

Eva shows what a provider said a request cost, and marks an estimate as an estimate. It never multiplies tokens by a rate and calls the result a cost.

Type `/cost` in the console to see what the current Session has spent.

## Cost and Estimate are different things

**Cost is what the Provider said a request cost.** Eva records it in Ticks —
integers of 1e-10 USD — so no rounding creeps in across thousands of small
charges.

**An Estimate is what a Run's counters come to at published prices.** It is a
projection. It moves when a vendor reprices, because it is folded fresh each
time rather than stored.

Eva shows an Estimate marked as one. An Estimate read as a Cost is exactly the
mistake that keeping two words apart exists to prevent.

## Absent is not zero

If a Provider does not report a cost, Eva records absent. **Absent is never
rendered as zero**, and Eva never computes a number from tokens times a rate
and presents it as a Cost.

A Run that cannot report its cost says so in words. That is a Degraded outcome:
Eva keeps the data, marks it, and holds it out of any scoring.

## Why integers

A float of dollars accumulates error. At 1e-10 USD per Tick, a Run costing
three cents is 300,000,000 Ticks, and a million such Runs still add up exactly.

## What is coming

Cost attributed per task, per merged change, and per harness is the "one bill"
part of Eva's pitch, and it lands with the multi-harness work.
[The roadmap](/about/roadmap) says when.


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