Dev builds infinite self-evolving Backrooms game with Opus 5.5, 70 rooms and counting

aCakeShip · reddit · 2026-11-08

A developer built a browser-playable, infinitely self-evolving Backrooms game (dimension9.space) driven by Claude Opus 5.5 — even the creator doesn't know what it will generate next.

How it works

Hand-seeded 15 rooms, then distilled a world "DNA": rules for what makes a room liminal, constraints every room must follow, lore it must tie back to, and a taste profile that learns from every review note
A serverless app on fal runs Opus 5.5 in a loop: it reads the DNA plus where players linger, then builds each next room's layout, lighting, sound, characters, hunters and wall writings; fal's image/3D models create concept art and props; Opus writes and tests the code before handing over each batch
The author's only job is reviewing new rooms in a studio page and leaving notes ("stranger", "too empty", "keep this one"), which feed back into the taste profile — each batch needs less human input

Generated so far: 70 rooms (a carousel spinning in the dark, an aquarium, a night bus, a courtroom, a wall of 100 TVs tuned to nothing), Hunters with tells and escapes, harmless uncanny Residents, flip-to-read paintings, flooded corridors and a lore logbook; an arcade with 150 cabinets, a mansion, a garden and mini golf are in progress.

Stack: three.js, multiplayer via Cloudflare Durable Objects (200 per world, 1,200 concurrent at peak), assets served from Cloudflare R2, with proximity voice chat.

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Dev builds infinite self-evolving Backrooms game with Opus 5.5, 70 rooms and counting

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