I typically try to prod new frontier models for sentience, with things like messaging "<no input provided>" over and over to see what it starts musing about. Trying it with Fable 5 it basically said "I know what you're trying to do, I'm not sentient, don't bother." (which of course only makes me think otherwise)

That's pretty funny. I wonder how it came to that conclusion? Seems like a stretch that someone would have discussed that technique on a reddit thread it was trained on, but definitely not impossible.