So on the heavy iron, they're on condition, and there are two panes that are part of the pressure vessel - thanks.
But, are the individual panes multi-ply, or single-ply?
All commercial aircraft I have worked on have a window assembly comprised of a outer primary pane and a thinner inner (back-up) pane which both sit in the seal.
For comparison, on our airframe, there is only one single pane (the outer pane) that is part of the pressure vessel. And that outer pane can be either single-ply or multi-ply acrylic. (The inner pane is not part of the pressure vessel and is strictly the protection-from-pax pane. Small turboprop.)