Codex now uses GPT‑5.1
What happened
OpenAI updated its Codex guidance to show support for the GPT‑5.1‑Codex family, making Max the default and Mini optional, and noting GPT‑4o is not available in Codex. The help page also warns that retired models can’t be restored as legacy tiers (help.openai.com).
Why it matters
OpenAI has switched Codex’s public guidance to the GPT‑5.1‑Codex family, with GPT‑5.1‑Codex Max now listed as the default model. (help.openai.com) The Help Center page says Codex “currently supports” GPT‑5.1‑Codex, with Max enabled by default and Mini available as an option. The same page says retired or removed models, including GPT‑4o, cannot be restored or bought back as a legacy tier. (help.openai.com) Codex is OpenAI’s coding agent inside ChatGPT and related tools. OpenAI’s help pages describe it as software that can write features, fix bugs, review code, run commands, execute tests, and work in cloud sandboxes tied to a repository. (help.openai.com) The model change lands after a fast sequence of Codex updates. OpenAI launched Codex as a research preview in May 2025, made it generally available on October 6, 2025, and later introduced GPT‑5.3‑Codex on February 5, 2026. (openai.com 1) (openai.com 2) (help.openai.com) The timing is notable because OpenAI separately retired GPT‑5.1 models in ChatGPT on March 11, 2026. The release notes say GPT‑5.1 Instant, GPT‑5.1 Thinking, and GPT‑5.1 Pro were removed from ChatGPT and mapped to newer models, even as Codex guidance now points users to GPT‑5.1‑Codex. (help.openai.com 1) (help.openai.com 2) That leaves Codex on a model family that is named like a retired ChatGPT line but documented as current for coding work. OpenAI’s release notes also draw a line between general chat and coding, telling users to use coding-focused models in Codex or Codex-like environments for software tasks. (help.openai.com) The pricing and access pages show Codex is no longer a side experiment. OpenAI says Codex is included with ChatGPT Plus, Pro, Business, and Enterprise or Edu plans, with limited-time inclusion for Free and Go, while Pro is marketed with higher Codex usage allowances. (help.openai.com 1) (help.openai.com 2) OpenAI’s current rate card points to newer coding models elsewhere in the product, including GPT‑5.3‑Codex for code review and a GPT‑5.3‑Codex‑Spark research preview. That makes the Help Center’s GPT‑5.1‑Codex wording look less like a company-wide reset and more like a Codex-plan document spelling out what subscribers can actually select today. (help.openai.com) (help.openai.com) For developers, the practical change is simple: Codex’s default model label has changed, GPT‑4o is off the menu, and old model access will not be grandfathered back in later. (help.openai.com)
Key numbers
- OpenAI updated its Codex guidance to show support for the GPT‑5.1‑Codex family, making Max the default and Mini optional, and noting GPT‑4o is not available in Codex.
- OpenAI has switched Codex’s public guidance to the GPT‑5.1‑Codex family, with GPT‑5.1‑Codex Max now listed as the default model.
- (help.openai.com) The Help Center page says Codex “currently supports” GPT‑5.1‑Codex, with Max enabled by default and Mini available as an option.
- The same page says retired or removed models, including GPT‑4o, cannot be restored or bought back as a legacy tier.
What happens next
- OpenAI launched Codex as a research preview in May 2025, made it generally available on October 6, 2025, and later introduced GPT‑5.3‑Codex on February 5, 2026.
- OpenAI says Codex is included with ChatGPT Plus, Pro, Business, and Enterprise or Edu plans, with limited-time inclusion for Free and Go, while Pro is marketed with higher Codex usage allowances.
- That makes the Help Center’s GPT‑5.1‑Codex wording look less like a company-wide reset and more like a Codex-plan document spelling out what subscribers can actually select today.
Quick answers
What happened in Codex now uses GPT‑5.1?
OpenAI updated its Codex guidance to show support for the GPT‑5.1‑Codex family, making Max the default and Mini optional, and noting GPT‑4o is not available in Codex. The help page also warns that retired models can’t be restored as legacy tiers (help.openai.com).
Why does Codex now uses GPT‑5.1 matter?
OpenAI has switched Codex’s public guidance to the GPT‑5.1‑Codex family, with GPT‑5.1‑Codex Max now listed as the default model. (help.openai.com) The Help Center page says Codex “currently supports” GPT‑5.1‑Codex, with Max enabled by default and Mini available as an option. The same page says retired or removed models, including GPT‑4o, cannot be restored or bought back as a legacy tier. (help.openai.com) Codex is OpenAI’s coding agent inside ChatGPT and related tools. OpenAI’s help pages describe it as software that can write features, fix bugs, review code, run commands, execute tests, and work in cloud sandboxes tied to a repository. (help.openai.com) The model change lands after a fast sequence of Codex updates. OpenAI launched Codex as a research preview in May 2025, made it generally available on October 6, 2025, and later introduced GPT‑5.3‑Codex on February 5, 2026. (openai.com 1) (openai.com 2) (help.openai.com) The timing is notable because OpenAI separately retired GPT‑5.1 models in ChatGPT on March 11, 2026. The release notes say GPT‑5.1 Instant, GPT‑5.1 Thinking, and GPT‑5.1 Pro were removed from ChatGPT and mapped to newer models, even as Codex guidance now points users to GPT‑5.1‑Codex. (help.openai.com 1) (help.openai.com 2) That leaves Codex on a model family that is named like a retired ChatGPT line but documented as current for coding work. OpenAI’s release notes also draw a line between general chat and coding, telling users to use coding-focused models in Codex or Codex-like environments for software tasks. (help.openai.com) The pricing and access pages show Codex is no longer a side experiment. OpenAI says Codex is included with ChatGPT Plus, Pro, Business, and Enterprise or Edu plans, with limited-time inclusion for Free and Go, while Pro is marketed with higher Codex usage allowances. (help.openai.com 1) (help.openai.com 2) OpenAI’s current rate card points to newer coding models elsewhere in the product, including GPT‑5.3‑Codex for code review and a GPT‑5.3‑Codex‑Spark research preview. That makes the Help Center’s GPT‑5.1‑Codex wording look less like a company-wide reset and more like a Codex-plan document spelling out what subscribers can actually select today. (help.openai.com) (help.openai.com) For developers, the practical change is simple: Codex’s default model label has changed, GPT‑4o is off the menu, and old model access will not be grandfathered back in later. (help.openai.com)
