GitHub makes GPT‑5.3‑Codex the default base model for Copilot Business and Enterprise

GitHub said on May 17 that GPT-5.3-Codex is now the base model for all Copilot Business and Copilot Enterprise organizations, replacing GPT-4.1 when an administrator has not explicitly selected another model. The change applies to the default path that generates suggestions across those paid organizational plans, according to GitHub’s changelog. GitHub said the switch does not apply to Copilot Pro, Pro+, or Free. The company had previously announced the base-model and long-term-support changes on March 18. ### If a team did nothing, what changed on May 17? May 17 was the date GitHub made GPT-5.3-Codex the active base model for Copilot Business and Enterprise organizations, according to the company’s changelog. GitHub said the base model is the one used when an organization does not explicitly choose another model. (github.blog) GitHub’s documentation says base models apply only to Copilot Business and Copilot Enterprise. The docs describe a 60-day upgrade window after designation, followed by automatic enablement on organizations and enterprises as the base model. ### Where would developers actually notice the switch? GPT-5.3-Codex had already been rolling out across GitHub Copilot surfaces before becoming the base model. (github.blog) GitHub said in February that the model would be available in the model picker in Visual Studio Code across chat, ask, edit and agent modes, as well as in GitHub Mobile, Copilot CLI and the Copilot coding agent. (docs.github.com) GitHub’s changelog entry on the base-model switch ties the change to organizations that have not chosen a different model. In practice, that means the default suggestion path changes for teams that rely on organization-wide defaults rather than per-user model selection. That inference is based on GitHub’s description of how base models work in Copilot Business and Enterprise. (github.blog) ### What happened to GPT-4.1? GPT-4.1 was the prior base model for those organizational plans, and GitHub said GPT-5.3-Codex replaces it. GitHub’s May 17 changelog says GPT-4.1 will remain force-enabled at a 0x multiplier for the time being, but will deprecate alongside the launch of usage-based billing on June 1, 2026. (github.blog) June 1, 2026 is also listed in GitHub’s supported-models documentation as the closing-down date for GPT-4.1 in Copilot. The same documentation lists GPT-5.3-Codex as generally available. ### Why did GitHub pair this with long-term support? March 18 was also the date GitHub designated GPT-5.3-Codex as its first long-term-support model for Copilot Business and Enterprise, according to a separate changelog post. (github.blog) GitHub said designated LTS models will remain available for 12 months from launch, and said GPT-5.3-Codex launched on February 5, 2026. (docs.github.com) GitHub said GPT-5.3-Codex will remain available through February 4, 2027 for Copilot Business and Enterprise users. In that March post, the company said Copilot data showed the model had a “significantly high code survival rate” among enterprise customers. ### What should administrators and engineering leads check now? (github.blog) GitHub’s docs say the base model has a 1x premium request multiplier on paid plans. Separate billing documentation says Copilot Business and Copilot Enterprise include pooled per-user GitHub AI Credits allowances at the billing-entity level, with interaction cost depending on both model and token use. (github.blog) Version support may also matter. GitHub’s supported-models page says Visual Studio Code v1.108 and later provides improved prompting and response quality for GPT-5.3-Codex. GitHub’s May 17 changelog says teams that need more time can contact their account team, while the next dated milestone in the transition is June 1, 2026, when GPT-4.1 is set to deprecate with usage-based billing. (docs.github.com 1) (docs.github.com 2)