GitHub Copilot CLI adds a “Rubber Duck” mode that uses a different AI model than the main one for second opinions

GitHub has added an experimental Rubber Duck mode to Copilot CLI.

The mode has a separate AI model review the main model’s work during coding tasks.

It can use different models such as Claude, GPT-5.4, and Gemini to provide a second opinion.

This could improve code quality and outcomes on complex, long-running multi-file tasks and debugging.