Copilot cost is approximated at one US cent per AI unit

Copilot cost is computed as 1 US cent per AI unit, from the AI-unit total the Copilot CLI reports per session (stored as NanoAiu, see decision 12).

Why: GitHub’s pricing communication is ambiguous. One cent per AI credit (not unit) is documented only for the credit-based plans, which are deprecated; precise pricing for the usage-based plans is not yet available. Until it is, the approximation is used and labelled as such in the dashboard’s FAQ. Storing the raw AI units keeps the quantity intact for a later, exact conversion — or for a CO₂ factor per AI unit, should one become available — and the historical data can then be recomputed.