In BriefOn Monday, OpenAI launched Codex, an agentic coding tool marketed to software developers. Today, OpenAI also launched a new model designed to turbo-charge Codex: GPT-5.3 Codex. The new model release notably follows hot on the heels of a new agentic coding model released by its competitor, Anthropic. Indeed, OpenAI and Anthropic had originally planned to release their two agentic coding tools at the exact same time: 10 a.m. PST. However, not long before the original release time, Anthropic moved its release date up by 15 minutes, slightly besting OpenAI in the race to publicize the models.