GPT-5.3-Codex: OpenAI's Autonomous Coding Agent Redefines Software Engineering

GPT-5.3-Codex achieves 56.8% on SWE-Bench Pro, 77.3% on Terminal-Bench 2.0, and 64.7% on OSWorld. Here's how OpenAI built an agent that helps train itself and what it means for the future of software engineering.