Anthropic has added a new system prompt rule, identified as "tengu_heron_brook," to its Claude Code tool (version 2.1.314, released October 30) and the Claude Opus 5.5 model to prevent the recreation of specific existing video games. The rule explicitly instructs the model to build original games, genre-based games, or games from user designs and assets, while prohibiting recreations of specific titles even if renamed. Anthropic software engineer Addy Osmani confirmed the change was implemented to steer Opus 5.5 away from IP infringement, aligning with the company's usage policy. The modification was first spotted by AI decompilation enthusiast "chasm" around October 27 and independently verified by XDA, which noted the rule identifier had served other purposes in prior versions. Despite the guardrail, the measure is unlikely to significantly curb the broader trend of AI-assisted game cloning and porting. Early feedback on Anthropic's GitHub indicates the prompt is already interfering with legitimate game development workflows, suggesting the restriction may produce false positives for developers building original projects.