I have no idea in ACI but in Spain I think the only tying requirement would be the bars keep the intended form and position throughout the whole concreting operation.
So you may tie all, part, or even weld (prefab rebar grill, never at the works site) within the specific code conditions that apply.
Most of the ICF forms do not require rebar tying. Although I cannot speak for all, many of the engineered ICF wallsystems we have done, are designed as a worst case for bar placement. The horizontal bar is already held in a fixed location, usually through the integral plasit locator clips on the form system. As for the vertical bars, they are restricted to a maximum lateral movement of 8", due to the structural ties which are formed with the block at 6-8 inches on center. So if the wall system is speced for 16" centered bar placement, the design is calculated for 24" centered bar placement, which is the absolute worst case. As for the perpendicular movement, because the horizontal bars are secured in the clips in an alternating pattern, the vertical bars can be "woven" into the horizontal bar to effectively create a basket weave pattern. ICF forms are great to engineer with, simply because the forms design allows for a much more consistent and ideal design placement on site, of all reinforcing.
