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Earthfall, made by an agent.

A short film and four levels, from one request to its closing card. An agent made all of it through Gamesteel's tools: every model, painting, sound, song and line of script. The person who asked wrote seven messages.

Earthfall's opening film, the way the game plays it: a minute, with its own music and sound, recorded from the game in a browser from its first frame to the moment it hands over the controls.

How it was made

  1. The ship in orbit over the Earth as the film opens, its log reading: course home, ground control no reply.

    One request.

    It began as one message to Claude Code: “…I want to see how you make cinematics, I want you to make one of a spaceship from the space falls into earth and crashes and I can start walking on the earth”. Before it touched anything, the agent read Gamesteel's guide to the engine.

    guide start · game · scripts · art · sound · playtest

  2. The ship falling through the clouds at sunrise, burning, its readout counting down the altitude and the speed.

    What moves, built in 3D.

    The ship, her pilot, a deer and a villager are models it wrote as short scripts. Gamesteel rendered them in Blender, frame by frame (the wing tearing away, the pilot climbing out), and handed back art the game can draw.

    art model kestrel · kestrel-torn · pilot · deer · villager

  3. A painted valley under the cloud: forest down to a clearing, a river plain beyond, snowy mountains in a pink dawn.

    The rest, painted.

    The valley under the cloud, the canyon walls, the village's land at dawn: 26 paintings, made by code on a canvas in the game's own colours. It stepped the game forward, stopped where it wanted, and looked at each one where it is drawn.

    art paint vista · gorgeback · houses · ashground-a playtest look

  4. The pilot beside the burning wreck at dusk, as words from the radio run along the bottom: anyone out there? This is Ashvale.

    Every sound designed, the music composed.

    23 sounds designed in layers and six pieces of music, from the orbit to the wood at night. Each came back to it in numbers and words (how loud, how bright, whether it clicks, whether a part is buried), and it tuned by those what it cannot hear.

    sound design alarm · tear · impact · owl sound compose orbit · descent · wood listen

  5. The Gorge at night: the pilot on a ledge beside a burning piece of the wing, the helmet lamp lighting the canyon, a waterfall pouring off the far wall behind and a ladder up the near one.

    Levels in text, the rest in scripts.

    Earthfall's game text is 234 lines, its four levels laid out in it, tile by tile, in words you could type by hand; the film, the lamp and the flares are about 2,900 lines of scripts beside it.

    write_code edit script.set game · lib:film · lib:gorge · lib:ashvale

  6. The ending, in Ashvale at dawn: the pilot and a villager with a lantern on the road between the cottages, and the words: Come in. You're home.

    Played to the end.

    When it thought it was done, it played what it built with the keys a player has and mended what did not work: a creek too deep to climb out of, a ledge that blocked the jump beneath it, a ladder top you could not step off. Then it played all four levels to the end.

    playtest until · playtest play · playtest look

What it took

The real numbers, from the three sittings Earthfall was made in.

Model
Claude Opus 5.5, in Claude Code, through Gamesteel's MCP tools One agent, from the first request to the last level.
Time
About 4 hours 1 h 28 min for the first film; 2 h 31 min for the 3D models, a better film and three more levels, while the person who asked was away; then 12 min mending what they saw in these pictures.
Asked
Seven messages The request; then that the game was laggy and should look more realistic; a pick between two looks it offered; and that the fall from space should have no cut. For the upgrade, one sentence (“make the BEST cinematic you can do, and gameplay”) and a “keep going”. Then, seeing these pictures, that the gorge's backdrop looked broken, a waterfall and a house floated, and the dirt looked bad.
Tokens
About 1.2 million, written by the model Its scripts, levels, models, paintings, sounds and songs, and its reasoning along the way.
Cost
About $125 at Anthropic's API list prices Most of it is the model reading its own work again as it goes. On a Claude plan it counts against the plan's usage instead.

Hours count the time the agent spent working; pauses of ten minutes or more are left out. Prices are Claude Opus 5.5's published API rates.

Make your own.

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