GitHub Copilot CLI just landed four new generally available features, and two of them are worth stopping for. The headline additions are Rubber Duck , a built-in second-opinion agent that critiques your work using a model from a completely different AI family , and on-device voice input that transcribes your speech locally without ever touching a cloud API. Both shipped at Microsoft Build 2026 and are live now on every paid Copilot tier.
The Problem with One Model Reviewing Itself
The goal of Rubber Duck is to catch early planning mistakes before they compound into harder-to-fix downstream errors , a known weakness of single-model AI agents. The core issue is structural: a model reviewing its own output can only catch what its training allows it to see. The same blind spots that caused a bug are the same blind spots that will prevent it from noticing one.
Rubber Duck is a built-in review agent that runs alongside your main Copilot CLI session. After drafting a plan, mid-implementation on something complex, or after writing tests, the primary agent hands its work to the rubber duck for a second opinion. The rubber duck looks for blind spots, design flaws, and overlooked edge cases. It reports back with concrete, actionable feedback , it doesn't make file changes. Your main agent decides what to do with the feedback.
The architectural decision that makes this genuinely interesting: the critic always comes from a different model family than your session model.
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