I asked GPT5 directly about fake system prompts.

> Yes — that’s not only possible, it’s a known defensive deception technique in LLM security, sometimes called prompt canarying or decoy system prompts.

…and it goes into details and even offers helping me to implement such a system. It says it’s a challenge in red-teaming to design real looking fake system prompts.

I’d prefer “Open”AI and others to be open and transparent though. These systems become fully closed right now and we know nothing about what they really do behind the hidden doors.