Microsoft Build 2026: Project Polaris — Microsoft's Own AI Model Replaces GPT-4 in GitHub Copilot by August

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Microsoft unveiled Project Polaris, a homegrown mixture-of-experts coding model that will replace GPT-4 Turbo as the default GitHub Copilot engine starting August 2026 with a three-month opt-out fallback period. Polaris outperforms GPT-4 Turbo on HumanEval and MBPP benchmarks with particular gains in Rust and Haskell, runs on Microsoft's custom Maia AI accelerators, and gives Pro subscribers multi-file context up to 100,000 lines. This is Microsoft's most significant move to reduce OpenAI dependency — they now control model, inference infrastructure, and developer experience end-to-end.