Update on September 23, 2025: GPT‑5-Codex is now available to developers using Codex via API key (in addition to being available to developers using Codex via their ChatGPT subscription). GPT‑5 Codex is available at the same price as GPT‑5, and is available in the Responses API only. The underlying model snapshot will be regularly updated. Check out the Codex developer documentation(opens in a new window) and changelog(opens in a new window) for more details.
Today, we’re releasing GPT‑5-Codex—a version of GPT‑5 further optimized for agentic coding in Codex. GPT‑5-Codex was trained with a focus on real-world software engineering work; it’s equally proficient at quick, interactive sessions and at independently powering through long, complex tasks. Its code review capability can catch critical bugs before they ship. GPT‑5-Codex is available everywhere you use Codex—it’s the default for cloud tasks and code review, and developers can choose to use it for local tasks via Codex CLI and the IDE extension.
Since we first launched Codex CLI(opens in a new window) in April and Codex web in May, Codex has steadily evolved into a more effective coding collaborator. Two weeks ago, we unified Codex into a single product experience connected by your ChatGPT account, enabling you to move work seamlessly between your local environment and the cloud without losing context. Codex now works where you develop—in your terminal or IDE, on the web, in GitHub, and even in the ChatGPT iOS app. Codex is included with ChatGPT Plus, Pro, Business, Edu, and Enterprise plans.
With these updates, Codex moves closer to what we’ve been building toward all along—a teammate that understands your context, works alongside you, and reliably takes on work for your team.
GPT‑5-Codex
GPT‑5-Codex is a version of GPT‑5 further optimized for agentic software engineering in Codex. It’s trained on complex, real-world engineering tasks such as building full projects from scratch, adding features and tests, debugging, performing large-scale refactors, and conducting code reviews. It’s more steerable, adheres better to AGENTS.md(opens in a new window) instructions, and produces higher-quality code—just tell it what you need without writing long instructions on style or code cleanliness.
GPT‑5-Codex adapts how much time it spends thinking more dynamically based on the complexity of the task. The model combines two essential skills for a coding agent: pairing with developers in interactive sessions, and persistent, independent execution on longer tasks. That means Codex will feel snappier on small, well-defined requests or while you are chatting with it, and will work for longer on complex tasks like big refactors. During testing, we've seen GPT‑5-Codex work independently for more than 7 hours at a time on large, complex tasks, iterating on its implementation, fixing test failures, and ultimately delivering a successful implementation.
On OpenAI employee traffic, we see that for the bottom 10% of user turns sorted by model-generated tokens (including hidden reasoning and final output), GPT‑5-Codex uses 93.7% fewer tokens than GPT‑5. Conversely, for the top 10%, GPT‑5-Codex thinks more, spending twice as long reasoning, editing and testing code, and iterating.