Claude Opus 4.6 vs. GPT-5.3 Codex: How I shipped 93,000 lines of code in 5 days

I put the newest AI coding models from OpenAI and Anthropic head-to-head, testing them on real engineering work I’m actually doing. I compare GPT-5.3 Codex with Opus 4.6 (and Opus 4.6 Fast) by asking them to redesign my marketing website and refactor some genuinely gnarly components. Through side-by-side experiments, I break down where each model shines—creative development versus code review—and share how I’m thinking about combining them to build a more effective AI engineering stack. — What you’ll learn: - The strengths and weaknesses of OpenAI’s Codex vs. Anthropic’s Opus for different coding tasks - How I shipped 44 PRs containing 98 commits across 1,088 files in just five days using these models - Why Codex excels at code review but struggles with creative, greenfield work - The surprising way Opus and Codex complement each other in a real-world engineering workflow - How to use Git concepts like work trees to maximize productivity with AI coding assistants - Why Opus 4.6 Fast might be worth the 6x price increase (but be careful with your token budget) — Brought to you by: WorkOS—Make your app enterprise-ready today — Detailed workflow walkthroughs from this episode: • How I AI: GPT-5.3 Codex vs. Claude Opus 4.6—Shipping 44 PRs in 5 Days: https://www.chatprd.ai/how-i-ai/gpt-5-3-codex-vs-claude-opus-4-6 • How to Combine Claude Opus and GPT-5.3 Codex for High-Velocity Code Refactoring: https://www.chatprd.ai/how-i-ai/workflows/how-to-combine-claude-opus-and-gpt-5-3-codex-for-high-velocity-code-refactoring • How to Redesign a Marketing Website Using Claude Opus 4.6 for Creative Development: https://www.chatprd.ai/how-i-ai/workflows/how-to-redesign-a-marketing-website-using-claude-opus-4-6-for-creative-development — In this episode, we cover: (00:00) Introduction to new AI coding models (02:13) My test methodology for comparing models (03:30) Codex’s unique features: Git primitives, skills, and automations (09:05) Testing GPT-5.2 Codex on a website redesign task (10:40) Challenges with Codex’s literal interpretation of prompts (15:00) Comparing the before and after with Codex (16:23) Testing Opus 4.6 on the same website redesign task (20:56) Comparing the visual results of both models (21:30) Real-world engineering impact: 44 PRs in five days (23:03) Refactoring components with Opus 4.6 (24:30) Using Codex for code review and architectural analysis (26:55) Cost considerations for Opus 4.6 Fast (28:52) Conclusion — Tools referenced: • OpenAI’s GPT-5.3 Codex: https://openai.com/index/introducing-gpt-5-3-codex/ • Anthropic’s Claude Opus 4.6: https://www.anthropic.com/news/claude-opus-4-6 • Cursor: https://cursor.sh/ • GitHub: https://github.com/ — Other references: • Tailwind CSS: https://tailwindcss.com/ • Git: https://git-scm.com/ • Bugbot: https://cursor.com/bugbot — Where to find Claire Vo: ChatPRD: https://www.chatprd.ai/ Website: https://clairevo.com/ LinkedIn: https://www.linkedin.com/in/clairevo/ X: https://x.com/clairevo — Production and marketing by https://penname.co/. For inquiries about sponsoring the podcast, email [redacted email].