Key Takeaways Dynamic thinking capability: GPT-5-Codex can spend anywhere from seconds to seven hours on coding tasks, adapting its processing time based on complexity. Superior performance metrics: T...
OpenAI announced on September 15, 2025, the release of GPT-5-Codex, a specialized version of its flagship GPT-5 model optimized specifically for software engineering tasks. The upgrade represents a significant advancement in AI-powered coding assistance, bringing enhanced autonomous capabilities and dynamic reasoning to developers worldwide.
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.
The standout feature of GPT-5-Codex is its ability to dynamically allocate computational resources based on task complexity. The company says its new model, called GPT-5-Codex, spends its "thinking" time more dynamically than previous models and could spend anywhere from a few seconds to seven hours on a coding task.
In a briefing, OpenAI's Codex product lead Alexander Embiricos said that much of the increased performance was thanks to GPT-5-Codex's dynamic "thinking abilities."
Users may be familiar with GPT-5's router in ChatGPT, which directs queries to different models based on the complexity of a task. Embiricos said GPT-5-Codex works similarly but has no router under the hood and can adjust for how long to work on a task in real time.
This dynamic approach provides a significant advantage over traditional routing systems. Embiricos says this is an advantage compared to a router, which decides how much computational power and time to use on a problem at the outset.
Instead, GPT-5-Codex can decide five minutes into a problem that it needs to spend another hour. Embiricos said he's seen the model take upward of seven hours in some cases.
GPT-5-Codex demonstrates substantial improvements across multiple coding benchmarks. On SWE-bench Verified, an evaluation based on real-world software engineering tasks, GPT‑5 scores 74.9%, up from o3's 69.1%.
The model also shows significant gains in code refactoring tasks, with GPT-5-Codex scored nearly 20 percent higher than the default model, which is simply called GPT-5.
OpenAI has specifically tailored GPT-5-Codex for real-world software engineering scenarios. 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.
The model's training extends to code review capabilities, addressing a common pain point in AI-assisted development. OpenAI says that GPT-5-Codex has been "trained specifically for conducting code reviews and finding critical flaws."
According to the company, Codex currently handles "the vast majority" of proposed changes to code being written by OpenAI staffers, "catching hundreds of issues every day—often before a human review begins."
The upgrade comes amid intensifying competition in the AI coding tools market. AI tools for software engineers, also known as vibe coders, have surged in popularity in recent months. The CEOs of Google and Microsoft claim that roughly 30% of their companies' code is now written by AI.
All that vibe coding has made the businesses behind AI coding platforms some of the fastest-growing in tech. Cursor, among the most popular AI coding tools, reached annualized revenue of around $300 million in April and is reportedly raising new funds at a $9 billion valuation.
OpenAI's move appears strategic in this competitive landscape. Now, OpenAI wants a piece of the pie. The ChatGPT maker has reportedly closed on a deal to acquire Windsurf, the developer behind another popular AI coding platform, for $3 billion.
GPT-5-Codex is currently available to ChatGPT subscribers across multiple tiers. The new model is now rolling out in Codex products, which can be accessed via a terminal, IDE, GitHub, or ChatGPT, to all ChatGPT Plus, Pro, Business, Edu, and Enterprise users. OpenAI says it plans to make the model available to API customers in the future.
The rollout includes comprehensive platform integration. Access to Codex is included for OpenAI users with ChatGPT Plus, Pro, Business, Edu, and Enterprise plans, with usage limits scaling based on which plans a user subscribes to.
OpenAI explicitly notes that Plus, Edu and Business plans will cover "a few focused coding sessions each week," while users on the Pro plan can expect a "full workweek across multiple projects."
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