He spent 45 minutes and €20 of tokens to one-shot a game from 'the most dangerous AI model'
Koen van Gilst handed Fable 5 a game idea he'd carried for years and asked for it in one go. Out came a single 2,319-line HTML file with zero dependencies. Then the thread told him the game already existed on the Game Boy Advance.
After 45 minutes and over €20 in tokens, Fable 5 reported 'Shepherd's Dog is complete' as one self-contained HTML file. The author's verdict: the first time a model built his vision in a single attempt.
The catch the thread surfaced: this exact sheep-herding game exists in dozens of versions, so the one-shot is less invention than a polished recall from training data.
A years-old idea, built in one prompt
Koen van Gilst's write-up is the rare light note in the Fable week. He took a game concept he'd had for years, handed it to Anthropic's Fable 5 (the model the press has been calling "the most dangerous"), and asked it to build the whole thing in a single shot. The result, in his words: "after 45 minutes and more than €20 worth of tokens (!), it happily reported that 'Shepherd's Dog is complete — a single 2,319 line index.html with zero dependencies.'" One file, no external dependencies, play-tested and shipped. For van Gilst, a Tech Lead, the headline was that it matched his vision on the first try: "the first time an AI model is able to create this for me in one go."
You can play it directly — a link the author admits he botched in the original post.
"I played this on the Game Boy Advance"
The thread's first move was to deflate the "idea I've had for years" framing.
"There are countless examples of this exact game. I played this on the Gameboy Advance! There's like 50 of them on the App Store right now… It's the describing it as 'an idea I've had for years' that rings weird." — a commenter who recognized the game from the GBA
Van Gilst took it on the chin, in the thread:
"a quick Google search would've told me that this game has been made several times before, also way before I ever had this idea. Apparently it's a pretty obvious game idea." — the author, conceding the point
The interesting part: it's a benchmark, not a birth
Once the originality claim was dropped, the thread found the real signal: this is a useful yardstick precisely because so many versions exist to compare against.
"what's surprising to see is how well done this one is compared to the other tries. The controls and movement are smooth, the animations aren't jittery, the ui makes sense, there's a clear progression in difficulty. This model clearly 'understands' the implementation of this game far better than the others did." — a commenter comparing it to earlier model attempts
A broader caution followed: code was never the bottleneck in games.
"It is like writing novels: it is not the spelling or typing on the keyboard that is the bottleneck. It is always the creative world building part… The same holds for software." — a longtime HN regular
What the €20 actually bought
The honest read is that Fable 5 didn't invent a game; it reconstructed a well-trodden one cleanly, in one pass, with polish that earlier models fumbled. That's a real capability jump and a deflated origin story at the same time. The benchmark value is genuine: a known, much-cloned game is a fair test of how well a model turns a vague description into something playable. The "most dangerous model" framing, against a tired cartoon sheepdog, is the joke the title is in on.
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