ChatGPT’s latest model, built for developers and coders, was “instrumental in creating itself,” according to OpenAI. The latest update, ChatGPT 5.3 Codex, is aimed at developers who want tools to write and develop code faster than ever.
The blog post from OpenAI says, “The Codex team used early versions to debug its own training, manage its own deployment, and diagnose test results and evaluations — our team was blown away by how much Codex was able to accelerate its own development.”
ChatGPT wasn’t the primary development tool for this latest model, but GPT 5.3 Codex suggested refinements and improvements throughout the process. OpenAI says it helped to accelerate research, analyze interaction quality, and propose fixes for issues.
OpenAI says 5.3 Codex began working on improvements to itself, starting from its “early versions.” The company also says many researchers and engineers now say their jobs have “fundamentally” changed in the last couple of months because of these changes.
In an interview with Ars Technica in December, OpenAI’s product lead for Codex, Alexander Embiricos, alluded to improvements in the model’s feedback loop. He said, “I think the vast majority of Codex is built by Codex, so it’s almost entirely just being used to improve itself.”
OpenAI now says its new Codex 5.3 runs 25% faster than previous versions while using fewer resources. You can now access the model through paid ChatGPT plans, with API access coming soon.
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OpenAI’s CEO, Sam Altman, has been clear in the past that it aims to develop AI-powered researchers to help it improve its own models. For example, he said in October last year that he wanted to build an AI research intern by September 2026 and a “true automated” AI researcher by March 2028.
Disclosure: Ziff Davis, PCMag’s parent company, filed a lawsuit against OpenAI in April 2025, alleging it infringed Ziff Davis copyrights in training and operating its AI systems.
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