Fable 5.1 agents build a walkable browser 3D city for $33, MIT-open
A forkable MIT pipeline turns OpenStreetMap and USGS data into navigable Three.js cities — 453 buildings, playable interiors, agent-run recon and QA.
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A walkable city for $33
The creator says Union Square, San Francisco cost about $33 in API fees and roughly 8M tokens, built in around 2 hours by Fable 5.1 subagents running self-QA loops. That buys 453 buildings, 129 storefronts, cable cars, and 220 pedestrians you can actually walk through in a browser tab.
The pipeline is the real product
It runs in four stages: parallel recon agents pull OpenStreetMap geometry, USGS elevation, and storefront data with confidence scores; Blender scripts bake reusable GLB kits; pure Three.js assembles the runtime; then Playwright screenshots get graded against reference photos by a swarm of architect, geographer, technical-artist, and interaction-designer reviewer agents. Every stage is MIT-licensed and forkable.
What you could ship this weekend
Fork it, point the recon stage at any place with OpenStreetMap and USGS coverage, and `npm run dev` gives you a browser-native reconstruction — no game engine, deployable as a single self-contained HTML via `npm run viewer`. The two reference worlds show the range: a photoreal Union Square and a cel-shaded, zero-binary-asset Higashiyama, Kyoto (266 buildings, 1,938 trees).
The honest caveat
This is a community project, not an Anthropic release, and the cost and time figures are the author's own. HN's top comments argue Claude Opus 5 does comparable geometry for less, and the textures are rough — the constructive fix floated is pairing LLM-generated low-poly silhouettes with diffusion-model textures. Treat it as a proof-of-concept pipeline to learn from, not a turnkey world engine.