GitHub Copilot’s default engine changes this month. Project Polaris, Microsoft’s own mixture-of-experts coding model, replaces GPT-4 Turbo as the out-of-the-box default for every Copilot subscriber, migrated automatically. Enterprise customers get an optional three-month fallback to GPT-4 Turbo through November if they need to validate the switch before committing; everyone else is moved over with no action required and no extra cost.
Microsoft is framing this as a performance upgrade, and it’s also a strategic one: it cuts Copilot’s dependency on OpenAI’s models for its default experience, something Microsoft has been building toward since it started letting Copilot users pick Claude and Gemini models manually. Polaris being the default — not just an option — is the bigger signal. Most developers don’t change defaults.
That matters for anyone whose team standardised on Copilot as “the AI coding tool” without much thought to which model sits behind it. The model doing the reasoning is changing under a name that hasn’t. Benchmarks Microsoft has published claim Polaris beats GPT-4 Turbo on standard coding tasks, but those numbers haven’t been independently verified yet, and coding-benchmark claims from any vendor are worth treating with some scepticism until they hold up in your own codebase.
So what
If your team runs on Copilot, budget a sanity check in the next few weeks: run your usual review workflow against a few real diffs and see whether output quality holds, especially on anything security- or domain-sensitive. This is also a useful moment to revisit the bigger question — Copilot, Cursor, and Claude Code all now let you choose or default to different underlying models, so “which AI coding tool” and “which model” are genuinely separate decisions, and the right answer for a regulated healthcare build isn’t necessarily the right answer for a fast-moving MVP. If you want a team that tracks this shift for you rather than defaulting to whatever ships in the box, see how we approach AI-assisted development or get in touch to talk through your stack.