Recently, Claude Opus 5.5 started receiving complaints from users over the AI’s sudden inability to work in tandem with Reverse Engineer Anything, the very same tool that allowed users to decompile and open-source video games. At the time, no rules or updates had officially been announced by Anthropic.

Today, however, we have confirmation that Anthropic is deliberately pushing back against its users’ love of vibe-coded IP theft slop, as a new rule (a flag in Claude Opus 5.5’s code titled “tengu_heron_brook”) instructs the AI to safeguard against prompts that produce “a recreation of a specific existing game, even if it is renamed or called original.”

The new rule was seemingly first spotted by a user on X, but first appeared in Claude Opus 5.5’s changelog on October 27. While the new rule isn’t too fond of recreations “of a specific existing game,” it does still allow users to “build original games, games in a genre, and games from the user’s own designs and assets.”

Claude Code picked up a new rule around Oct 27, sent from Anthropic’s servers under a flag called "tengu_heron_brook". There’s no setting to turn it off.

The full rule: “Do build original games, games in a genre, and games… pic.twitter.com/0Zc5mQWHJt

In simpler terms, this appears to be a step beyond just cracking down on decompilations; Claude will now actively stop its users from attempting to vibe-code an original game that is influenced by a pre-existing one.

For instance, asking it to make a racing game should be fine, but asking it to create a racing game “like Need For Speed ” would trigger Claude’s guardrails.

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