Karpathy gave a model one paragraph of Tolkien and $10. It wrote 5,500 lines of code.
Andrej Karpathy handed Claude Opus 5 the opening paragraph of The Lord of the Rings, a one-million-token budget worth roughly $10, and a single instruction: render it in three.js. The model worked for about two hours and produced some 5,500 lines of code that procedurally stage the scene. Karpathy called the result janky but said it marks the end of the era when you sized up a model by asking it for an SVG of a pelican on a bicycle. He also named the weakness the exercise exposed: the model cannot really watch what it builds, so it had to check its own work by taking screenshots, slowly and repeatedly, and it got things wrong along the way.
Why it mattersThe interesting number is not the line count, it is the price. Karpathy's point is that things nobody would ever commission — a custom world built for exactly one reader — become worth making when they cost ten dollars and an afternoon of machine patience. The bottleneck he identifies is now one of the clearest gaps in the field: models can write the code for a world, but they cannot yet see or play the thing they made, which is precisely how a person would tell whether it was any good.
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