chrisfirst Live-Builds an Island City of ~4000 Buildings with AI in UE5.9

On day one of Epic AI MegaJam, creator chrisfirst revealed this year's theme, Director's Cut: players star as a stunt driver on a film set, and every mission is a "shoot." Starting from a blank Unreal Engine 5.9 map, he built entirely live with AI; by the end of the stream, an island city with nearly 4,000 buildings and roughly 28,000 props had been generated—while his MacBook's fans screamed.

Confirmed

The world started as gray-box placeholders on an empty map, built out by Unreal Engine's built-in AI assistant; the layout can be saved and rebuilt at any time from the same layout
Buildings and props came from Epic's City Sample asset pack and street-scene props from the Fab store, replacing the earlier gray boxes
The protagonist's car, "Rat," was defined by AI concept art: a beat-up yellow sports car; the author asked for the chosen version to look even more worn, with a blue door and a "01" racing number on the side
The in-game "director" is a picky older woman on the radio who comments on the player's driving; her lines were written by AI, voiced with ElevenLabs, and generated in parallel with other tasks—the author's favorite line is "Easy on the Rat."

Why it matters

The thread showcases a complete end-to-end AI-assisted game development workflow: concept art, world building, layout persistence, and even dialogue and voice generation were done in-engine or via AI services. A single person can produce a city-scale scene within a Game Jam cycle that previously required a whole team—a tangible example of AI lowering the barrier to game development.

2026-11-13 ~ 2026-11-13 · 6 related posts

Primary sources

From empty UE5.9 map to a 4,000-building island city, built live with AI in one day — chrisfirst · 2026-11-13 14:39 (UTC+08:00)
AI swaps gray boxes for ~4,000 buildings and 28,000 props inside Unreal Engine — chrisfirst · 2026-11-13 14:39 (UTC+08:00)
UE 5.9's built-in AI assistant builds a city from gray boxes and saves the layout — chrisfirst · 2026-11-13 14:39 (UTC+08:00)

[source] From empty UE5.9 map to a 4,000-building island city, built live with AI in one day — chrisfirst · 2026-11-13
Epic AI MegaJam Day 1: 'Director's Cut' theme and the hero car revealed — chrisfirst · 2026-11-13
AI concept art picks the hero car: a beat-up yellow '01' named the Rat — chrisfirst · 2026-11-13
AI-written lines plus ElevenLabs voice give this game a tough radio director — chrisfirst · 2026-11-13
[source] UE 5.9's built-in AI assistant builds a city from gray boxes and saves the layout — chrisfirst · 2026-11-13
[source] AI swaps gray boxes for ~4,000 buildings and 28,000 props inside Unreal Engine — chrisfirst · 2026-11-13