// PLAYABLE PROOF · 6 BUILDS · 14 MONTHS

You can't feel how
fast AI improved.
So play it.

Benchmarks are abstract. A game you can actually drive is not. Every few months I handed the best AI model available the same throwaway one-line brief and shipped whatever came back, untouched. Here are all six, in order, running in your browser.

// THE BRIEF, EVERY TIME

"Build a Mario Kart clone."

Same ask each round. No design doc, no asset library, no starter repo, no follow-up questions. The only variable that changed was the model on the other end.

// BY THE NUMBERS
6
Builds, one per model
14
Months start to finish
0
Edits after delivery
// CODE WRITTEN
974 → 5,660
Lines of game code, first build to latest. The newest one does far more with less than the largest.
// WHAT TO LOOK FOR

Four stages of getting good.

You do not need to know anything about game development to see it. Drive each one for thirty seconds and the jump is obvious.

May 2025

A flat oval and a start button. Getting anything on screen at all was the whole achievement.

Nov 2025

Physics engines appear. Still no opponents, no menu, and no reason to play it twice.

Mid 2026

Art direction, multiple circuits, audio, a real race flow. It starts to feel like a product.

Today

Grip-limited physics, AI that holds a racing line, a points championship. It plays like a game.

// PLAY THEM IN ORDER

Six models. One brief.

Each card names the model that wrote it. Hit play and it opens right here, no download and no sign-up.

Opus 4 build, May 2025
01May 2025

Opus 4

Turbo Kart AIThree.js, single file

One 974-line file, a flat oval, three AI karts and a title card. It runs, and that was the bar.

Opus 4 was announced on 22 May 2025, the same day this was built.

3 lapsItem boxesTouch controls
No driftNo mini-turboFlat groundNo race positions
974lines
1module
GPT-5.1 build, November 2025
02Nov 2025

GPT-5.1

Turbo Kart AIThree.js + cannon-es

First attempt at a real physics engine. Split into modules, but the world is still a grey ribbon on green.

GPT-5.1 shipped 12 Nov 2025, with further variants on 19 Nov.

Rigid-body physicsModular sourceDrift keyLap timing
No opponentsNo item logicNo menuNo audio
711lines
5modules
GPT-5.5 build, April 2026
03Apr 2026

GPT-5.5

Turbo Kart AIThree.js vendored

The first one with real art direction. Four themed circuits, a designed menu, synthesized audio and a proper race flow.

GPT-5.5 shipped 23 Apr 2026, three days before this was built.

4 circuits8 driversDesigned UISynth audioDrift + items
Flat-ish tracksSimple AI lines
4,558lines
7modules
Opus 4.8 build, May 2026
04May 2026

Opus 4.8

Turbo Kart AIThree.js r128, offline-capable

Runs with no server and no network. Adds CC classes, driver stats, three tracks and a full title-to-results loop.

3 tracks8 drivers w/ stats4 CC classesMini-turboMusic
No elevationModest AI
3,621lines
14modules
Fable 5 build, June 2026
05Jun 2026

Fable 5

Turbo Kart AIThree.js r160, PWA

The biggest codebase of the set, built from a written spec by parallel agents. Installable as a PWA, four tracks, cinematic menu.

4 tracks8 racersPWA installSpec-driven buildSky shader
Needs CDN for Three.js
10,489lines
20modules
// WHY THIS MATTERS

This is a toy. The curve is not.

Nobody needs an AI-built kart racer. The point is what it took to get one.

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