Edit: From the TFA: Using the agent consumes GitHub Actions minutes and Copilot premium requests, starting from entitlements included with your plan.
[0] https://docs.github.com/en/copilot/managing-copilot/monitori...
(Source: I'm on the product team for Copilot coding agent.)
In my experience using Claude Sonnet 3.7 in GitHub Copilot extension in VSCode, the model produced hideously verbose code, completely unnecessary stuff. GPT-4.1 was a breath of fresh air.