Karpathy tests Opus 5: 5,500 lines of code written in two hours, but he still can’t even play the game he made - 36Kr

Andrej Karpathy had Claude Opus 5 turn the opening of The Lord of the Rings into a Three.js 3D scene that runs in a browser, and the model wrote about 5,500 lines of code over roughly two hours.

Developers are increasingly testing Opus 5 with games, physics simulations, and 3D scene building, highlighting its code generation and long-horizon task execution.

But these demos mostly measure system-building ability, not a mature world model.

The case also exposes clear gaps in continuous perception, video understanding, and self-verification, which still limit real-world use in games, animation, and custom software.