Claude Opus 4.6 vs GPT-5.3 Codex: Which AI Coding Assistant Should You Choose?

Claude Opus 4.6 vs GPT-5.3 Codex: A Developer’s Guide to the New AI Coding Landscape The core question: When Anthropic and OpenAI release flagship coding models on the same day, how should developers choose between them? In the early hours of February 2026, the AI industry witnessed a rare “head-to-head” moment. Anthropic released Claude Opus 4.6 at 2:00 AM. Just twenty minutes later, OpenAI launched GPT-5.3 Codex. Two leading AI companies unveiled their flagship programming models on the same day, leaving developers worldwide both excited and conflicted—which one should they use? This article synthesizes official release documentation and early adopter …