OpenAI released its new coding model, GPT-5.3-Codex, on Thursday. The model features improved reasoning and professional knowledge capabilities and operates 25 percent faster than its predecessor.
Anthropic, a primary competitor to OpenAI, launched its own coding model, Claude Opus 4.6, on the same day. Earlier this week, OpenAI introduced the Codex app for macOS, an interface designed for managing multiple AI agents simultaneously.
OpenAI described GPT-5.3-Codex as its first model that was instrumental in creating itself. The company stated that the Codex team used early versions of the model to debug its own training, manage its own deployment, and diagnose test results and evaluations.
In a blog post announcing the model, OpenAI wrote, “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.”
Anthropic recently made a similar claim about its Claude Cowork model. Engineers at both OpenAI and Anthropic report that almost all of their coding is now performed by AI.
The OpenAI blog post further states, “With GPT-5.3-Codex, Codex goes from an agent that can write and review code to an agent that can do nearly anything developers and professionals can do on a computer.”
