Simon Willison Builds Mini-Games Back-to-Back with Claude Opus 5.5

On October 15, 2026, Simon Willison had Claude Opus 5.5 Max in the Claude iPhone app build a Three.js game called Tree Appreciator. The gameplay involves spotting differences between two algorithmically generated trees, making it a spot-the-difference game. Claude ran for 3 hours 7 minutes and ultimately produced a game with music, animations, and an achievement system, reportedly quite playable. On October 16, Simon Willison used Claude again to build a new game: he used Claude Opus 5.5 Extra in Claude Code to create Chirp Pong, a two-player competitive Pong-style game that uses sound to communicate between two phones, implementing online two-player multiplayer entirely in HTML. There is no more detailed test feedback or follow-up on the game so far.

AI overview of reporting · Updated 3 days ago

1. 10/16 03:47 · 1 reports
   Using Audio Chirps to Enable Two-Phone Multiplayer Gaming
   Simon Willison：Chirp Pong
2. 10/15 05:23 · 1 reports
   Simon Willison Builds a Mini Game with Claude Opus 5.5
   Simon Willison：Tree Appreciator