This post is literally about a language the author invented to be hard for LLMs to parse and isn't in their training set and yet Opus 5 scored 68.8% on it.
You may agree with the author (that it doesn't mean it understands the language) but it's pretty hard to argue that this is copied form the training set.
You may agree with the author (that it doesn't mean it understands the language) but it's pretty hard to argue that this is copied form the training set.