Claude Code on Opus 5.5 refuses to clone existing games

Around October 27, Anthropic added two sentences to Claude Code’s prompt on Opus 5.5, so a request to rebuild a specific existing game, even renamed or labelled “original”, should now be refused, and chasm, who spotted the rule on X, reports there is no setting to turn it off. Original games, genre games and games built from your own designs and assets are meant to keep working, though developers’ complaints on GitHub show refusals reaching ordinary game work too.

The rule comes from Anthropic’s servers under the flag tengu_heron_brook. Its full text:

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

An Anthropic spokesperson pointed Game Developer to a post on X by Addy Osmani, a member of Anthropic’s technical staff. He wrote that the lines went in “to steer it away from recreating someone else’s specific game because using Claude to infringe IP is against our usage policy,” and that Anthropic would “continue to iterate to ensure we’re striking the right balance.” Tom’s Hardware, writing before that confirmation, called chasm’s wording plausible given the clear refusals developers had been running into over the past week.

Where the refusals land

Some of those refusals hit work that doesn’t look like cloning. Tom’s Hardware counts a run of GitHub issues on Claude Code’s repo about refusals of standard game work halfway through development, of replicating a game mechanic and of patching a tabletop-like game. Users also report blocks on harmless reverse-engineering, including runs with the popular Reverse Engineer Anything (REA) tool, which the outlet says may be linked to the rule. Some of the complaints may come from people with bad intentions, it adds, but at least one is from a developer with a real track record.

The exception rests on ownership: “the user’s own designs and assets.” Game Developer says it is unclear how the software would tell whether a user actually owns a game idea or its assets.

Why games, and why now

Moonlighter developer Digital Sun changed plans for the public beta of ReVamp, citing “the recent spate of games being reverse-engineered and cloned using the latest version of Anthropic’s LLM, Claude Opus”. Its playtest moved from Steam to a smaller one on Discord, a change the studio announced on October 19, per Kotaku. The same outlet describes the problem as Opus 5.5 decompiling a game’s code and rebuilding it, work that used to take determined coders months to years. Alliance Arts delayed its Steam Next Fest demo of Drunken Goddess Reflex for a similar reason: it feared the demo could be used to imitate the game’s presentation and gameplay “with AI or other tools” and that such works “could be released before our launch”.

Game Developer reports that developers have also pressed Valve on how it will keep these clones from supplanting their games on Steam, and that Valve gave developers in South Korea a rare explanation earlier this week. Tom’s Hardware adds that some developers have been hit by extortion scams threatening to turn their demos into full games before the originals ship.

How much it stops

Game Developer’s Bryant Francis writes that the rule may deter only the most low-effort copycats, since scientists and reporters have repeatedly documented that safety limits on generative AI tools can be sidestepped with rhetorical tricks. Many users replying to chasm made a blunter point: if Claude gets too hard to use, cloners can switch to open-weight models that carry no such restrictions. Against that, the protection is still only two sentences of prompt text.

For developers whose own projects get caught, Osmani wrote: “In the meantime, if Claude turns down something that’s yours, send it my way.”