Opus 5.5 has been autonomously improving an open-world NYC game for nearly a day

mattshumer_ · x · 2026-09-24

Matt Shumer reports that Opus 5.5 has been looping autonomously on his open-world New York City game for almost a full day, and the game keeps improving. Anyone can jump in and try it — the game is multiplayer.

It's a striking live demo of long-horizon agentic coding: a frontier model iterating on a large codebase for 24 hours without human intervention, without diverging.

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