Dev Builds SFSIM, a Live 3D Digital Twin of San Francisco with 1,000+ AI Citizens

On August 21, developer David (@davidfromkansas) posted a series of updates on his project SFSIM: a 3D digital simulation of San Francisco wired into real-time city data, populated by more than 1,000 synthetic citizens. He said he built it because he felt San Franciscans weren't online enough—so he simply made a "digital San Francisco."

Confirmed

• The simulator ingests real-time data streams including Muni, BART, ferries, bike-share, traffic, weather, earthquakes, and breaking news
• The city hosts over 1,000 synthetic citizens living their daily lives, active on the dedicated subreddit r/simfrancisco (related community)
• The 3D city is procedurally generated with Three.js, based on public geospatial data, building footprints, and crowdsourced information
• The building generation pipeline was built with Devin: given an address, it searches for information online via Exa to assist generation; the pipeline has produced roughly 170,000 buildings
• The simulator knows each building's real-world use (restaurant, commercial, residential, etc.), with models based on real-world public data

Why it matters

• David explains the project's motivation is to build a sandbox-style virtual game environment that simulates the social intelligence of personified agents with human-like needs and goals
• He believes such simulations matter for scalable AI alignment: agents can be trained to adopt helpful behaviors and observed in scenarios that are hard to replicate in the physical world
• He notes the techniques draw on more than a decade of academic research and says he has no PhD background; virtual environments can also provide spatial context for agents, useful for future training and observation
• The building data pipeline (Devin + Exa + Three.js) is itself a reusable workflow for procedural city generation

2026-08-21 ~ 2026-08-21 · 6 related posts

• Built a digital SF sim with 1,000+ synthetic citizens reacting to live city data — davidfromkansas · 2026-08-21
• [source] He put San Francisco in a simulator: 1,000+ AI citizens live on their own subreddit — davidfromkansas · 2026-08-21
• [source] Devin + Blender pipeline generates 174,647 buildings for a simulated San Francisco — davidfromkansas · 2026-08-21
• 3D SF buildings grounded in real data; future plans to train agents with spatial context — davidfromkansas · 2026-08-21
• Developer builds 3D virtual SF as training ground for AI agents, citing accessibility of techniques — davidfromkansas · 2026-08-21
• [source] Why build a simulated SF? To train agents' social intelligence and alignment — davidfromkansas · 2026-08-21