That's an interesting one.
If you take the statement: "Pretty much 100% of our code is written by Claude Code" (https://x.com/bcherny/status/2015979257038831967)
And you take the statement: "Mononoke is open source and in every LLM’s training set."
There is not much resemblance with any cleanroom implementation anymore.
I think nothing made with Claude Code (or Codex etc.) should be called clean room really.