GitHub Copilot CLI combines model families for a second opinion

Rubber Duck, a new feature introduced in GitHub Copilot CLI, is an experimental tool designed to improve coding accuracy by providing a second opinion on data pipeline plans and implementations. It operates as an independent reviewer by utilizing a second model from a different AI family to catch errors and offer feedback, especially for complex multi-file and long-running tasks. Evaluations indicate that the combination of Claude Sonnet and Rubber Duck significantly bridges the performance gap with Claude Opus, particularly in challenging scenarios. Rubber Duck is activated automatically or upon user request during critical checkpoints such as after drafting plans or writing tests, helping to identify architectural issues, bugs, and cross-file conflicts. The feature is currently available in experimental mode and can be accessed with the /experimental command in Copilot CLI, offering enhanced review capabilities for users selecting any Claude model paired with GPT-5.4.

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