Claude Opus 5.5 Generates 134KB Real-Time 3D City in One Prompt

Starting September 24, developer gandamuml showcased a 134KB single-file real-time 3D city demo generated by Claude Opus 5.5 from a single prompt, cheekily named "grand theft code", and said it runs on his MacBook. He explained it was a defiant response to critics who called his earlier demos "AI slop" and "not small enough". The next day he released "Grand Theft Code 2": a mere 165KB executable containing three 3D cities (NYC, Nara, Chongqing) with music, claiming Opus 5.5 designed the entire system itself.

Confirmed

• The first demo is 134KB, single-file, real-time 3D, generated by Opus 5.5 from one prompt and runs on a MacBook (per gandamuml)
• The author acknowledged much of the code is essentially the product of RL training, with humans mainly bootstrapping
• The demo was made in response to criticism of his earlier work as "AI slop" and "not small enough"
• On September 26 the author revealed his method: the first generation lacked detail, so he had Opus build its own asset tools, adding details like fire escapes and finer vehicles
• "Grand Theft Code 2" is a 165KB executable with three cities (NYC, Nara, Chongqing) and music; the author says Opus 5.5 designed the whole system

Unconfirmed

• "Could be smaller on Windows or Linux" is only the author's speculation, untested
• No independent third-party verification of the generation method, file size, or sequel contents beyond the author's own statements

Why it matters

• A runnable, extremely small real-time 3D city from a single prompt—expanded the next day into a multi-city executable—vividly demonstrates the boundaries of Opus 5.5's long-code generation and engineering integration capabilities
• The author's disclosed workflow of having the model build its own asset tools, plus his admission that most code is RL-generated, offers a first-person perspective on where frontier model coding ability comes from (RL training vs. human guidance) and sparked community debate over the substance of AI-generated code

2026-09-24 ~ 2026-09-26 · 8 related posts

• Opus 5.5 generates a ~134KB realtime 3D city demo, "grand theft code" — gandamu_ml · 2026-09-24
• [source] Claude Opus 5.5 generates ~134KB realtime city demo that runs on a MacBook — gandamu_ml · 2026-09-24
• Claude Opus 5.5 generates a ~134KB realtime city demo, dubbed 'grand theft code' — BuffMcBigHuge · 2026-09-24
• "Petty by design": dev explains his Opus 5.5 city demo was built out of spite — gandamu_ml · 2026-09-25
• [source] Claude Opus builds GTA-style game with 3 cities and music in a 165KB executable — gandamu_ml · 2026-09-25
• 134KB realtime city demo by Opus 5.5 sparks 'how did you do that' reactions — timalphena · 2026-09-26
• [source] How the 134KB realtime city demo was made: Opus builds its own tiny asset tools — gandamu_ml · 2026-09-26

1 near-duplicate retellings: pandag0n