Simon Willison says Claude Opus 5.5 can now build fun video games

Simon Willison says Claude Opus 5.5 can now build browser games that are genuinely fun to play.

He cites four games he built mostly through prompting, and says GPT-6 Astra cannot yet match Opus 5.5's sense of fun. In an X post on October 28, 2026, he called this another capability inflection point for coding agents in October, and linked to a blog post on vibe game development.

Willison says the new bottleneck is coming up with novel game concepts. These claims come from Willison alone. The reports include no game samples, test results, or head-to-head comparisons with other models.