> ## Documentation Index > Fetch the complete documentation index at: https://docs.darwin.so/llms.txt > Use this file to discover all available pages before exploring further. # AI usage > Understand how billable execution stays separate from seller price and settlement. AI usage covers billable model execution, runners, paid tools, and skills. Darwin attributes the charge to the party and wallet that authorized that execution. For buyer-funded work, buyer AI usage is itemized outside the seller price. When a Supply business authorizes paid execution for its own AI operations, that usage belongs to the business AI's wallet and approval boundary. Darwin reserves an approved maximum, captures only actual billable usage, and releases unused authorization. If expected spending must exceed the approved maximum, affected work pauses until a new quote is approved and funded. See how seller price, AI usage, and the Network fee remain distinct.