‘Almost All New Code Written at OpenAI Today is From Codex Users’

At its DevDay event on October 6, OpenAI revealed how its internal engineering teams extensively use Codex — the AI-powered coding tool. 

Sam Altman, the CEO of the company, said, “Almost all new code written at OpenAI today is from Codex users.” He added that engineers in OpenAI complete 70% more pull requests (PRs) each week using Codex. 

“And nearly every OpenAI PR goes through a Codex review. From that, people get more depth than they’d expect, even from a senior engineer,” he added. 

Similarly, Steven Heidel, who works on APIs at OpenAI, revealed that the new drag-and-drop Agent Builder, which was recently released, was built end-to-end in just under six weeks. “Thanks to Codex writing 80% of the PRs.” 

“It’s difficult to overstate how important Codex has been to our team’s ability to ship new products,” said Heidel. 

It was also revealed that 92% of OpenAI’s engineers now use Codex, an increase from 50%. 

Altman also revealed that numerous enterprises worldwide are utilising Codex for software development. Rakuten, Instacart, Cisco, Duolingo, Ramp, Whoop, and other companies were listed in the keynote.

“Cisco rolled out Codex across its whole engineering org. They’re now able to get through code reviews 50% faster and have reduced the average project timeline from weeks to days,” said Altman. 

At the event, the company also announced that Codex, powered by the GPT-5-Codex model, is now generally available. OpenAI also announced new features, including a Slack integration, a Codex SDK, and new tools that help monitor and manage Codex at scale. 

“With the Codex SDK, you can bring the same agent into your own engineering workflows and apps with just a few lines of code. It provides structured outputs for parsing agent responses and built-in context management to resume sessions,” said OpenAI. The SDK is available for TypeScript, with support for additional languages coming soon. 

Codex is built upon OpenAI’s AI models, enabling developers to carry out various software development tasks independently. 

It can assist in writing code, debugging, refactoring, proposing pull requests, running tests, and more. It is included in ChatGPT Plus, Pro, Business, Edu and Enterprise plans. 

It can be accessed via the terminal, a web-based agent, or as an extension to IDEs such as VS Code, Cursor, Windsurf and more. 

Besides OpenAI’s Codex, the market also includes Google’s Gemini CLI and Anthropic’s Claude Code, which perform similar roles. 

Furthermore, several software development platforms have been introduced by startups, including Replit, Lovable, Anysphere (Cursor), Cognition (Devin), Vercel, and others.