The gist showsmthat the first line ofmthe system prompt must be "You are Claude Code, Anthropic's official CLI for Claude."

That’s a reasonable attempt to enforce the ToS. For OpenCode, they also take the next step of additionally blocking a second line of “You are OpenCode.”

There might be more thorough ways to effect a block (e.g. requiring signed system prompts), but Anthropic is clearly making its preferences known here.