Is the xh a1s better in low light than the xh a1 (previous version)? How does it compare to a Z7 or Z5 or HMC 150?

I can only comment on the A1 vs A1s question. I don't believe there's a difference. As far as I know, nothing in the optical "chain" has been changed with the new model.

That's correct, the chips are the same, digital processing the same. The S model only has some minor operational upgrades.

Most of the 1/3" chip cameras are very close in light sensitivity. I've compared the XH A1 to the Sony Z1 and found that the XH A1 is maybe just a little bit better under very low light conditions, but the difference is negligible. I found the Sony to be better when a high gain is used--ie., the Canon got pretty noisy at +12 db while the Sony didn't look too bad at +12db.

I agree with Bill, the A1 isn't as good as the Z7 either and hence probably the Z5 now.

I said the XH A1 was a tiny bit better than the Z1 but the Z1 is better when using high gain. But under most production conditions you wouldn't use high gain. I wouldn't, anyway.

From what I've gathered, looking at side by side comparison shots, the Z7 (and I suppose the Z5) performs noticeably better in low light than the Z1. I haven't seen a side by side comparison with the A1, but since the Z1 and A1 are pretty close, I would think the Z7 (and Z5) also outperforms the A1 in low light.

Yes, the new Sonys are better than the A1 in low light. So is my Panasonic HMC150.
But there is so much more to a cam than that. In my opinion the A1 remains overall, very competitive with the Sonys.

I've compared a sony fx1000 to my xh-a1 and like Bill said, Sony is better in handling higher gain values. Even at gain values going up to 15-18 the fx1000 picture still looked quite good. The grain on the Sony much finer and less noticeable. I never go higher then 6db gain with my a1, 12gain just looks bad. I rather compensate with a lower shutter to squeeze better low light performance out of it and ofcourse a dimmable videolight.

I also compared the fx1000 to a vx2100 and when both lenzes were wide both showed allmost the same low light sensitivity, only when you started to zoom in the vx2100 hardly lost any sensitivity while the fx1000 became much darker quickly.