GitHub switches Copilot to GPT-5.3-Codex

GitHub changed the default model behind Copilot Business and Copilot Enterprise on May 17, making GPT-5.3-Codex the base model for those plans and replacing GPT-4.1. The company disclosed the switch in a GitHub Changelog post and said it applies to all organizations on those two plans, not to Copilot Pro, Pro+, or Free. (github.blog) That matters because the base model is the one Copilot uses when an organization has not pinned another option. (docs.github.com) In practice, for many large customers, a base-model change is not a feature launch so much as a product change delivered through the admin layer. GitHub’s documentation says base models apply only to Copilot Business and Copilot Enterprise and are automatically enabled after the upgrade window. (github.blog) ### What exactly changed on May 17? May 17 was the date GitHub said GPT-5.3-Codex would become the base model for all Copilot Business and Copilot Enterprise organizations. The company’s changelog says the model now replaces GPT-4.1 as the default for those customers. (github.blog) GitHub’s March 18 documentation had previewed the move and described a 60-day upgrade window before automatic enablement. That timeline put the switchover on May 17, which is the date GitHub later confirmed in its changelog. ### Which customers are included, and who is not? (docs.github.com) Copilot Business and Copilot Enterprise are the only plans covered by this base-model change, according to GitHub’s changelog and docs. GitHub said the update does not apply to Copilot Pro, Copilot Pro+, or Copilot Free. The same documentation shows that individual users can still encounter a broader model menu through GitHub Copilot’s supported-model system. (github.blog) GitHub’s model reference lists multiple OpenAI, Anthropic, and Google models in Copilot, which means the base-model switch sits inside a wider multi-model product rather than replacing model choice altogether. (docs.github.com) ### Why is GPT-5.3-Codex more than a routine default swap? March 18 is also when GitHub designated GPT-5.3-Codex as its long-term support, or LTS, model for these enterprise Copilot tiers. GitHub’s docs say the LTS designation is intended to give enterprises a longer availability window for planning, reviews, and upgrades. (github.blog) February 4, 2027 is the end of the published LTS availability window for GPT-5.3-Codex. That gives large organizations a dated support horizon, which is unusual in a market where frontier-model turnover has often been faster than enterprise procurement cycles. That last point is an inference from GitHub’s published LTS window and the company’s decision to label this model for long-term support. (docs.github.com) ### What happens to GPT-4.1 now? GPT-4.1 is not disappearing immediately from enterprise Copilot. GitHub said GPT-4.1 will remain force-enabled at a 0x multiplier for the time being, though the company also said it will deprecate alongside the launch of usage-based billing on June 1, 2026. (docs.github.com) June 1 therefore becomes the next operational date for admins watching model behavior, billing, and internal defaults. GitHub told customers that teams needing more time should contact their account team. ### Where does this fit in GitHub’s broader Copilot rollout? (github.blog) February 9 was when GitHub said GPT-5.3-Codex became generally available for GitHub Copilot, with administrators on Business and Enterprise plans required to enable the model policy in Copilot settings. Later, on February 25, GitHub expanded availability across github.com, GitHub Mobile, Visual Studio Code, and Visual Studio through the model picker. (github.blog) May 17 turned that optional model into the base experience for enterprise tiers. The next published milestone is June 1, when GitHub says GPT-4.1 will deprecate alongside usage-based billing, and the longer-dated milestone is February 4, 2027, when GPT-5.3-Codex’s LTS window ends. (github.blog 1) (github.blog 2)