Claude Fable 5.0 vs ChatGPT 5.5 - Test on real code

Fable 5 (Claude's new "Mythos" model) just dropped, so I put it head-to-head with GPT 5.5 (Codex) on my actual production SaaS — Scripti.ai — instead of toy benchmarks. I ran both models across four real-world tests: finding bugs, fixing them, redesigning UI, and a full security audit. The results were not close. Here's exactly what each model found in my codebase, where Codex fell flat, and why I'm going all-in on Claude. What you'll learn: — What Anthropic's "Mythos" model actually is and how Fable 5 relates to it — How Claude Fable 5 and GPT 5.5 (Codex) compare on real production code, not benchmarks — Why Fable found 23 real bugs (overcharging, credit race conditions, promo abuse) while Codex found 1 — The bold pricing-page redesign Fable shipped vs Codex's "live app polish" — A real security audit: self-granting paid tiers, promo redemption races, a leaking debug router, rate-limit bypass — Where Codex actually wins (dependency hygiene / NPM advisories) and why that's not enough — My honest take on Codex usage limits and why I'm going back all-in on Claude Codex Masterclass:    • ChatGPT Codex Masterclass: Complete Beginn...   Claude Code Masterclass:    • Claude Code Masterclass: Complete Beginner...   Build Your First SaaS:    • Build Your First SaaS in 3 Hours (using Cl...   My Links: Build real AI apps with me: https://www.skool.com/luke Script & package your videos with AI: https://scripti.ai Raw tech news with no tracking: https://techl8.com Chapters: 0:00 — Fable 5 is out (and it's basically Mythos) 0:25 — What Mythos actually is 1:20 — Build With Luke (the community) 2:15 — The benchmark table + test setup 3:17 — The real codebase: Scripti.ai 4:06 — Test 1: Bug hunt (23 bugs vs 1) 8:40 — Test 2: UI redesign 11:40 — Test 3: Security (the main event) 13:54 — Verdict: I'm going all-in on Claude Contact: [email protected]