But I've heard of models of at least a partially liquid Jupiter.

But the liquid is hydrogen, not water. We can tell by its mass that Jupiter is mostly hydrogen, but the conditions of temperature and pressure there are so extreme that most of our concepts of solid/liquid/gas don't apply. The atmosphere we see is a very thin skin atop a massive sphere of material in conditions we can't even duplicate in earth laboratories. And these conditions vary enormously as we go towards the center.

I've even heard speculation that the planet might have a core of crystalline hydrogen behaving like a superconductor (hence the extravagant magnetic field).