GPT-5.3-Codex Becomes the Copilot Business and Enterprise Base Model
On May 17, 2026 GitHub flipped the default Copilot model on Business and Enterprise plans from GPT-4.1 to GPT-5.3-Codex. GPT-4.1 stays free until June 1, then it falls under usage-based billing. Here is what changes for pinned models in your repo and CI.