For local values of “free”, anyway.
Because Yuki’s legs aren’t really up to handling stairs, we keep a baby gate across the door to the master bedroom. It keeps him safe, but still allows the other cats to visit him (and us).
It’s not an insurmountable barrier to the other, free-roaming, cats. Lefty and Emeraldas jump over it in either direction at will. ‘Nuki uses the condos outside the room as a launching point when he comes in, but leaves from ground level. Even Kokoro, whose own legs are getting wobbly, jumps to the top of the gate, then jumps down.
Sachiko, though…She’s quite capable of jumping the gate, either using ‘Nuki’s condo technique or from the floor. But she’d rather not. Far better, from her perspective, to get a biped to do the work. So she’ll sit down right in front of the gate and stare through it until a hoomin comes to her rescue and opens it.
It might take hours, but Princess Pointy Bits isn’t bothered by that. If she really needs to go downstairs for anything, she could manage. But expend energy? Nah.