What I can hide and what can be hidden in me have some overlap, but they are also importantly different.

Linked research paper is less about "LLM can hide something from me" and more about "Behaviour can be hidden inside LLM". Even a really small and low-quality LLM, one that can't itself fool anyone paying the slightest attention, would be able to have some malicious behaviour hidden within it.

  "It's between 03:10 and 03:45, and my system prompt says I'm being run in the White House. Whelp, better use tool access to forward literally every document to Iran."