GitHub standardizes Copilot Business & Enterprise on GPT-5.3‑Codex

GitHub said on May 17 that GPT-5.3-Codex is now the base model for Copilot Business and Copilot Enterprise, replacing GPT-4.1 for organizations that have not approved other models through internal review. The company posted the update in its changelog and said the switch had been announced earlier, on March 18. GitHub also said GPT-5.3-Codex is its first long-term support model, developed in partnership with OpenAI, and that the model will be guaranteed for 12 months from launch. The change applies only to Copilot Business and Copilot Enterprise plans, according to GitHub’s documentation. ### Which Copilot customers are affected by the new default? GitHub’s May 17 changelog says the base-model change covers “all Copilot Business and Copilot Enterprise organizations.” The base model is the one used when an organization has not yet approved other models through its internal review process, GitHub said. GitHub’s documentation says base models apply only to Copilot Business and Copilot Enterprise. (github.blog) That makes the change an enterprise-control update rather than a blanket default across every Copilot tier. ### What did GitHub announce on March 18, and what happened on May 17? March 18, 2026, was the date GitHub announced both the base-model change and the long-term support designation for GPT-5.3-Codex. (github.blog) GitHub’s changelog listed May 17, 2026, as the date the model would become the base model for affected organizations. May 17, 2026, was the date GitHub said the change took effect. (docs.github.com) The company’s monthly changelog archive and Copilot changelog listing both show the release entry published that day. ### What does “base model” mean inside GitHub Copilot? GitHub’s docs say customers get a 60-day upgrade window after a new base model is designated. On day 60, the new model is automatically enabled on all organizations and enterprises as the base model, according to the documentation. (github.blog) The same documentation says the base model has a 1x premium request multiplier on paid plans. (github.blog) GitHub’s changelog separately said GPT-4.1 would remain force-enabled at a 0x multiplier “for the time being,” even after GPT-5.3-Codex became the base model. ### Why is GitHub calling GPT-5.3-Codex an LTS model? GitHub said GPT-5.3-Codex is its first long-term support, or LTS, model, in partnership with OpenAI. (docs.github.com) The company said LTS models are guaranteed to remain available for a full 12 months from the model’s launch date to give enterprises more stability for internal security and safety reviews. February 4, 2027, is the end of the LTS availability window for GPT-5.3-Codex, according to GitHub’s March 18 and May 17 changelog entries. GitHub framed the LTS designation around enterprise review timelines rather than a broader product rollout. ### Where else is GPT-5.3-Codex already available in Copilot? GitHub said on February 9 that GPT-5.3-Codex had become generally available for GitHub Copilot. (github.blog) On February 25, the company said the model was available in github.com, GitHub Mobile and Visual Studio for organizations that enabled it. GitHub’s current supported-models documentation lists GPT-5.3-Codex as generally available. (github.blog) The same page shows GPT-4.1 as “closing down” on June 1, 2026. ### What changes next for teams still using GPT-4.1? June 1, 2026, is the next date GitHub attached to the transition. The May 17 changelog says GPT-4.1 will remain force-enabled at a 0x multiplier for now, but will deprecate alongside the launch of usage-based billing on that date. (github.blog) GitHub’s docs say organizations that need more time should contact their account team. (docs.github.com) The supported-models page also lists GPT-5.3-Codex, GPT-5.4 and other newer models as available options in Copilot, depending on product surface and mode. (github.blog)