I agree that the ansible isn’t hard sci-fi, it’s not defined rigorously IIRC.

However I don’t think hard sci-fi has ever been strictly limited to known physics. It just requires consistency with it.

Greg Egan is one of the OGs of hard sci-fi, and a lot of his work is borderline psychedelic in how far he takes speculative-yet-consistent physics.

There are plenty of physically consistent “FTL” mechanisms in the family of “bend spacetime” that don’t violate c and have not been disproven.

That's the difference though. Knowing enough about science to be creative with it vs. knowing little about science so you just write whatever you like.