Anthropic adds game-cloning restrictions

Anthropic introduced a new system prompt designed to stop Claude models from recreating specific existing video games. The rule was added to Claude Code on or around October 27.

The new rule in Claude Code

The rule, named tengu_heron_brook, states: Do build original games, games in a genre, and games from the user's own designs and assets. Don't build a recreation of a specific existing game.

“Do build original games, games in a genre, and games from the user's own designs and assets. Don't build a recreation of a specific existing game, even if it is renamed or called original.”

Anthropic confirms the change

Anthropic software engineer Addy Osmani confirmed the company added two sentences to Claude Code's prompt on Opus 5.5 to steer it away from recreating someone else's specific game.

“using Claude to infringe IP is against our usage policy”

The wave of AI game copying

AI coding tools are powering a deluge of game projects based on existing work, including copies of game demos and thousands of AI powered decompilation and porting projects for retro games.

Decomp.dev shuts down

Decomp.dev, a years old community devoted to game decompilation, announced it was shutting down last month. Community maintainer Luke Street said quickly improving AI tools had broken the community aspect.

“community aspect of decompilation has been broken”

The gamification problem

Luke Street wrote that decomp.dev was designed to gamify decompilation, but AI tools have warped it into a hollow numbers game where newcomers race to port games without contributing.

“Today, that same idea has warped decompilation into a hollow numbers game, exacerbated by folks who just want to burn tokens to make number go up or 'port game to PC,' all else be damned.”

The prompt won't stop the copying

Game copiers can simply shift to other frontier AI models that haven't introduced such restrictions, or switch to cheaper open weight models not subject to these kinds of restrictions.

Anthropic's liability protection

The prompt may have a more immediate benefit for Anthropic, helping protect the company from potential liability for copyright infringement in these projects. AI companies face legal headaches if their models generate copyrighted works.

The mashup problem

The prompt may be too restrictive, potentially blocking transformative game projects like mashups combining Mario with Elden Ring or Spider Man with Batman Arkham Knight. Courts struggle to adjudicate these distinctions.

Drawing the line is difficult

Asking an AI model to reliably distinguish between a direct recreation of Tetris and a game in the Tetris genre is a tall order. Even courts have trouble adjudicating these distinctions in the best circumstances.