Microsoft Build 2026: Project Polaris will replace GPT-4 inside GitHub Copilot in August
The interesting piece is the timing. Microsoft used the Build 2026 keynote on June 2 to retire GPT-4 Turbo as Copilot's default engine in favor of an in-house mixture-of-experts model running on its own Maia accelerators — the first product-level consequence of April's split with OpenAI.
Satya Nadella's Build 2026 keynote on June 2 was supposed to be about the Copilot super-app and Windows-as-agent-platform. What it actually delivered was the end of an era: Project Polaris, a Microsoft-trained mixture-of-experts coding model with specialized sub-modules per programming language, will replace GPT-4 Turbo as the default engine for every GitHub Copilot subscriber starting August 2026. Migration is automatic with an optional three-month GPT-4 fallback.
Microsoft is claiming gains on HumanEval and MBPP, with the largest deltas in low-resource languages including Rust and Haskell. Polaris runs on the company's custom Maia AI accelerators inside Azure rather than on OpenAI infrastructure — Microsoft's pitch is lower per-inference latency and lower operational cost, which matters when Copilot has tens of millions of paid seats and the bill is now Redmond's to control. Pro-tier subscribers also get multi-file context expanded to 100,000 lines and autonomous test generation.
Build also shipped a multi-agent extension for VS Code (general availability), Copilot Workspace GA, the GitHub Copilot desktop app in preview, and the MAI-Thinking-1 reasoning model — Microsoft's first in-house reasoning system, reportedly trained without OpenAI data. Together they are the most visible consequence yet of the April dissolution of the seven-year Microsoft/OpenAI exclusivity. The competitive read is straightforward: Microsoft now owns its own coding model, its own reasoning model, its own inference silicon, and the IDE everyone uses. The model layer just became one more thing it ships internally.
TechTimes — GitHub Copilot Replaces GPT-4 With Project Polaris, Ships Multi-Agent VS Code at Build → · AI Weekly — Microsoft Drops GPT-4 Turbo for Polaris in GitHub Copilot → · Engadget — Microsoft Build 2026: Live updates on Project Solara, Copilot AI, Windows, agents and more →