According to Geektime, the change surfaced after a user on X wrote that Anthropic had "started blocking reverse engineering of games". The new instruction allows original games, games in existing genres and games built on the user's own designs, but forbids recreating a specific existing game, even if the user changes its name or claims it is original.
Addy Osmani, a member of Anthropic's technical staff, confirmed that the company added two lines to Claude Code's instructions when it runs on Opus 5.5. He said using Claude to infringe intellectual property violates the company's usage policy and that developing original games will keep working as before. According to reports, the restriction is applied on the server side under an internal flag called tengu_heron_brook, and users cannot turn it off.
Reports on GitHub and Reddit describe false refusals: analyzing a Windows crash dump, software maintenance and security work, and building anti-cheat systems. It has not been shown that these refusals come from the new instruction rather than other safeguards, and Anthropic has not published an official announcement of the change.