Anthropic Adds a Claude Code Rule on Opus 5.5 That Blocks Recreations of Existing Games

Anthropic has added a rule to Claude Code, its AI coding assistant, that stops the tool from recreating specific existing video games when it runs on the Opus 5.5 model.

Anthropic confirmed the change through a post by Addy Osmani, a member of its technical staff, who said the company added two sentences to Claude Code’s prompt on Opus 5.5 to steer it away from rebuilding someone else’s game.

The rule reached Claude Code around October 27, according to X user Chasm, who first shared the change. Chasm reports that the instruction is delivered from Anthropic’s servers under a flag named “tengu_heron_brook” and that users cannot switch it off.

What the New Claude Code Rule Allows and Blocks

The instruction tells Claude to keep building original games, games in an established genre, and games based on the user’s own designs and assets. Recreating a specific existing game is off the table, and the rule says this applies “even if it is renamed or called original.”

In practice, the rule draws this line:

• allowed: original game concepts, genre games, and projects built from the developer’s own designs and assets
• blocked: a copy of a specific existing game, including versions that carry a new name or are described as original

Osmani says the reason is Anthropic’s usage policy, which already prohibits using Claude to infringe intellectual property. The prompt change makes Claude Code enforce that policy directly when a request targets a particular game.

Anthropic says it will continue to adjust the rule to strike the right balance. Osmani asked developers whose own projects are refused by Claude to send those cases to him directly.

Why Anthropic Is Targeting AI Game Clones

The change follows complaints about low-effort AI-generated games during Valve’s Steam Next Fest in October. Players reported that their feeds filled up with clones of existing games, including copies of titles that had only just released their own demos.

Some developers reacted by pulling public demos. The team behind Drunken Goddess Reflux, Alliance Arts and Who You, canceled its Steam demo plans in favor of private playtests. Valve responded that it would be “thinking about how to solve this problem.”

For developers who use Claude Code, the practical impact depends on the project. Original work and genre games should continue to work as before. Requests to reproduce a known game, or to rebuild one under a new title, now fail on Opus 5.5. Anthropic’s previous Claude launch, the Claude Duet background agent, was limited to paying subscribers, while the game rule is applied server-side to Claude Code on Opus 5.5 with no user setting to disable it.

Anthropic has not said whether a specific incident prompted the change, whether the rule will extend to other Claude models, or how it treats mods, decompilations, and recompilations of existing games.

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