Simon Willison says Claude Opus 5.5 can now vibe code games that are fun

Simon Willison reports building four browser games with Claude Opus 5.5 and argues October 2026 is an inflection point for vibe-coded games.

Simon Willison writes (Oct 28, 2026) that October marks a new inflection point, this time for vibe coding computer games. His claim is that Claude Opus 5.5 has improved at 3D modeling, music generation and, most importantly, game design. Earlier models could build something that looked like a game. He says Opus 5.5 can make one that is fun to play. For builders, the takeaway is that short, high-level prompts such as "Make it a LOT more fun" now produce real gameplay changes, not just visual polish.

Willison built four HTML/JavaScript games without reading the code, and all four run in the browser. Tree Appreciator came from a single prompt in the regular Claude chat. Emberwick, a 15-minute RPG, took extra playtesting to fix quest-logic bugs. Battle Drones is an RTS with multiplayer and LLM-vs-LLM matches, released under Apache 2.0. For a pumpkin-farming sim, he had Opus 5.5 Ultracode work for nearly two days. He says three.js prompts work well and that GPT-6 Astra "isn't quite there yet" on fun. He calls that an impression, not an exhaustive study.

Others report similar results. explainx.ai describes five multiplayer browser games built with Opus 5.5 in Claude Code on three.js and a Bun WebSocket server. Every's hands-on test found the model can "get carried away" and run out of time on the actual task.

According to Anthropic's docs, Opus 5.5 costs $4/$20 per million input/output tokens. The docs also list breaking changes from Opus 5, including that thinking can't be disabled.

Willison is candid about the limits. Each project took no more than four hours of his own time, and he won't enter them in game jams. The open question is what happens when someone with real design taste puts in the iteration.

Sources