Several open-source terminal agents are free and you bring your own key. Flint gives a free monthly allowance with no card, which is a different kind of free: nothing to set up first.
This is one of the questions people ask before they pick a tool rather than after, which is the right order. The rest of the answers are in the FAQ.
A desktop AI agent for Windows, built in Auckland, New Zealand. It reads your files, runs your terminal and drives your browser. Billed per token with a free monthly allowance and no subscription. See pricing, the FAQ, or who builds it.