Claude Fable 5 vs GPT 5.5 | Head to Head Coding Battle
I put Claude Fable 5 and GPT-5.5 into a real head-to-head coding battle to see which AI could build the better project. Both models got the exact same phased challenge and had to keep building on top of the same app as new features were added. This wasn’t just about writing code fast — it was about design, usability, creativity, polish, and which model could actually hold everything together as the project kept getting bigger. The phases were simple: Phase 1: a Windows-style desktop UI Phase 2: a working browser and physics sandbox Phase 3: a pseudo-3D racing game Phase 4: more desktop apps, features, and polish
Models2
Prompts4
Live HTML2
Files2
Video
Models Tested
GPT 5.5
Fable 5
Prompts Used
1Build the App
Build a Windows-style desktop UI in a single HTML file. Include: a desktop with icons, a taskbar with start menu, system tray, and live clock, draggable/minimizable/maximizable windows with smooth animations, and these working apps: a notepad with file save/load, a calculator with scientific mode, a file explorer with folder navigation, and a task manager showing real browser processes/memory/CPU usage with live-updating graphs. Add a settings app where you can change wallpaper and theme colors. Use a custom animated wallpaper that says "CLAUDE/GPT" in a cool futuristic neon style with particle effects. Make it look polished and modern.
2Working Browser & Sandbox Game
Add two new apps to the desktop: a working web browser (iframe-based with URL bar, back/forward/refresh, and tab support) and a physics sandbox game with gravity, draggable objects that bounce and collide realistically, a toolbar with tools like a gravity well, explosion button, and spawn different shapes with different materials (rubber, steel, wood).
3Build the Racing Game
Add a racing game app to the desktop. 3D perspective view with a road that curves and has hills, a car at the bottom of the screen with steering and acceleration, AI opponents on the track that you can overtake, lap timing with best lap tracking, a speedometer with RPM gauge, a minimap showing track position, and a garage screen where you can pick different cars with different stats (speed, handling, acceleration). Smooth 60fps with parallax background scenery — trees, mountains, buildings, sky that changes color. Keep it in the same HTML file.
4Feature Dump!
Add these apps and features to the desktop: Paint app — canvas drawing with brushes, eraser, shapes (rect, circle, line), fill bucket, text tool, color picker, and undo/redo. Support drag-and-drop images from my real desktop onto the canvas so I can edit them. Settings window — change wallpaper (pick from presets or upload your own), theme colors (dark/light/custom), accent color, window animation speed, and a toggle for taskbar position (bottom/top). Weather app — pulls live weather data with animated icons (rain, sun, clouds) and a 5-day forecast. Music player — drag audio files onto it, playback controls (play/pause/skip/seek/volume), audio visualizer bars that react to the music, and playlist support. Terminal app — working terminal with bash-like commands (ls, cd, cat, echo, mkdir, rm), command history with arrow keys, and a color theme matching the OS. Clock/Calendar app — live analog clock face, calendar view with today highlighted, and a countdown timer widget. System tray — volume slider, WiFi indicator, and a notification center that slides down from the top-right. Keep everything in the same HTML file. Make it feel like a real OS.