GitHub makes GPT-5.3-Codex Copilot base

GitHub has switched the default model underneath its paid workplace coding assistant for larger customers. In a changelog entry published May 17, the Microsoft-owned software platform said GPT-5.3-Codex is now the base model for Copilot Business and Copilot Enterprise, replacing GPT-4.1. (github.blog) The change applies to organizations on those two plans and took effect this week, according to GitHub’s changelog and product documentation. GitHub had previously flagged the move on March 18 as part of its base-model and long-term-support model schedule. (docs.github.com) ### Which Copilot customers are affected by the switch? GitHub’s May 17 changelog says the change applies to “all Copilot Business and Copilot Enterprise organizations.” The same documentation says base models apply only to those enterprise-focused plans, not to individual Copilot tiers. (github.blog) March 18 is the key date in GitHub’s rollout timeline. GitHub’s docs say that was the day it designated GPT-5.3-Codex as both the base model and the long-term support, or LTS, model, with automatic enablement set for Day 60. That schedule points to the May 17 change now reflected in the changelog. ### What changed from the previous default setup? (github.blog) GPT-4.1 was the prior default model for those organizations, and GitHub’s May 17 changelog says GPT-5.3-Codex replaces it as the base model. GitHub describes the base model as the default AI model Copilot uses when no other models are enabled for an organization. (github.blog) GitHub’s supported-models documentation shows GPT-5.3-Codex among the coding-focused models available in Copilot, while a separate model-comparison page lists GPT-4.1 as a general-purpose coding and writing model and GPT-5.3-Codex under agentic software development. That documentation frames the new default as a move from a general-purpose default toward a coding-agent model for enterprise tenants. (docs.github.com) ### Does GPT-4.1 disappear for enterprise users now? GitHub’s changelog says GPT-4.1 does not disappear immediately. The May 17 post says GPT-4.1 “will remain force-enabled at a 0x multiplier for the time being,” while the March 18 LTS post says it would deprecate alongside the launch of usage-based billing on June 1, 2026. (github.blog) June 1, 2026 is also the next date to watch in GitHub’s billing materials. GitHub’s pricing documentation says Copilot Business and Copilot Enterprise include per-user GitHub AI Credits allowances pooled at the billing-entity level, and that interaction cost depends on both model choice and token consumption. (docs.github.com) ### What does GitHub say about pricing and support windows? GitHub’s docs say the base model carries a 1x premium request multiplier on paid plans. The same page says customers were given a 60-day window to upgrade IDE extensions to versions that support the new model before automatic enablement. February 4, 2027 is the end date GitHub lists for GPT-5.3-Codex’s LTS availability window. (github.blog) GitHub says teams that need more time can contact their account team, according to both the March 18 and May 17 changelog entries. ### How long has GPT-5.3-Codex been in Copilot before becoming the default? February 9, 2026 is when GitHub said GPT-5.3-Codex became generally available for GitHub Copilot. (docs.github.com) In that announcement, GitHub called it “OpenAI’s latest agentic coding model” and said it was rolling out in Copilot after earlier testing. February 25, 2026 is when GitHub said administrators for Copilot Business and Enterprise could enable GPT-5.3-Codex in policy settings so users could select it in the model picker on GitHub.com, GitHub Mobile, Visual Studio Code and Visual Studio. (docs.github.com) The May 17 change moves that model from an opt-in choice to the default base model for those larger accounts. (github.blog) ### What should enterprise admins watch next? June 1, 2026 is the next operational milestone GitHub names in the rollout materials because that is when GPT-4.1 is set to deprecate alongside usage-based billing, according to the changelog. February 4, 2027 is the listed end of GPT-5.3-Codex long-term support, and GitHub’s model and billing pages remain the company’s reference points for admins tracking model availability, extension support and request costs. (github.blog 1) (github.blog 2) (github.blog 3)