Anthropic has changed the system prompt of Claude Code so that the tool steers away from re-creating particular video games that already exist. Original games, games in an established genre and games built from a user's own designs and assets are meant to keep working, according to Anthropic engineer Addy Osmani, who confirmed the change on social media on 30 October. The Verge and Ars Technica both reported on it on 2 November.
For most developers this is a small change. For anyone using an AI coding tool on ports, remakes, decompilations or game jam prototypes, it is a sign that model makers are starting to write their usage policies directly into the prompts their tools run on, and that requests can be refused for reasons that have nothing to do with code quality.
What changed and when
A user going by "chasm", who follows AI decompilation projects, spotted the new rule, which Ars Technica says appeared on or around 27 October. It sits in a JSON file under the name "tengu_heron_brook" and tells the model to build original and genre games and to avoid recreating a specific existing title, even when the user gives it a new name or calls it original. The two outlets quote that last clause slightly differently: The Verge has "named", Ars Technica has "renamed".
According to Ars Technica, XDA independently found the rule in version 2.1.314 of the Claude Code binary, released on 30 October. XDA also reported that the same internal name had been used for other purposes in earlier versions, and that Opus 5.5 appears to carry its own separate instructions against game recreations in its system prompt bundle. Osmani said the company added the two sentences to Claude Code's prompt on Opus 5.5 because using Claude to infringe intellectual property is against its usage policy. The Verge says it asked Anthropic whether other Claude system prompts will get similar changes.
Why Anthropic did it
The change comes amid a flood of AI-assisted game projects. Ars Technica describes thousands of decompilation and porting efforts for retro games and quickly assembled copies of game demos, which have made some developers wary of showing early work in public. The community site decomp.dev announced in October that it was shutting down; its maintainer, Luke Street, wrote that AI tools had broken the community side of decompilation as newcomers rushed to port games using work they had not contributed to.
Ars Technica argues the main benefit for Anthropic is likely legal: the rule may help shield the company from liability if people use its model for copyright infringement. Decompilation based on reverse engineering generally holds up legally when expressive elements such as art and sound are left out, the outlet notes, but nothing guarantees that individual users will be that careful.
Where the line gets blurry
Osmani said Anthropic will keep adjusting the balance and asked people to contact him if Claude refuses work that belongs to them. Ars Technica points to a handful of issue reports on Anthropic's GitHub suggesting the new prompt already gets in the way of some legitimate game development.
The harder cases are not straight clones. Ars Technica raises mashups that drop one game's character into another, and the gap between a copy of Tetris and a game in the Tetris genre, as questions courts struggle with, let alone a model following two sentences. The outlet also doubts the rule will slow the wider copying trend much, since users can switch to frontier models without such limits or to cheaper open-weight models that are not far behind.
What it means for teams using AI coding tools
The broader lesson goes beyond games. Behaviour of a coding agent can change between point releases because the vendor edited a prompt, not because the model or your code changed. A refusal that appears after an update may come from a policy rule like this one, and the fix is to describe your project accurately rather than to rephrase around it.
Teams doing legitimate work on their own titles, sequels or licensed ports should expect some friction while Anthropic tunes the rule, and should keep a record of what they own when reporting a wrong refusal.
What to do
- If Claude Code started refusing game work after version 2.1.314, check whether the request reads as a recreation of a specific existing game.
- When the game, its designs or its assets are yours, say so in the request, and report wrong refusals to Anthropic as Osmani invited.
- Keep art and sound assets you do not own out of decompilation and porting projects, whichever model you use.