It isnt flush.

Here is another photo of the wall

How could it possibly be flush? The quartz has depth, as would any backsplash material. What you’re ”seeing” in the photo, is an illusion.

If you look at the return around the window, it does look flush. A straight line with no zag. You would have to do your drywall work after the back splash was installed.

Now thinking of using a porcelain marble slab which is available in 1/4". Would probably need some type of Schluter profile to separate the two surfaces.

You can look at Porcelanosa, they have porcelain slabs and profiles. A few times a year they have good sale, like 40% off.

We used porcelain slab for fireplace, no profile just polished edges. But it was not easy to find a person to do cuts.

Future cracking will occur with that installation. It is pretty far from industry standards. Done to industry standards, large format porcelain is far more expensive than quartz. But it is at least more heat resistant. Quartz scorches aroond heat.

It’s a nice clean look but will be tricky (read that as expensive) to detail correctly- everyone will need to be on the same team.

@User, this particular one is put from 3 or 4 pieces

Having done a number of flush installations of things in this house, I can say that sometimes it starts at the framing. Sometimes it can be managed with different thicknesses of drywall. It's hard to sort out around openings like the window shown above. It can turn something that would take a couple hours, albeit spread out over some time and steps, (Window finished in the normal way, backsplash templated around the window and installed the normal way) to a process that takes a week or more, of labor. We actually made a model or two to figure things out.

@ Larry Wasson: what steps did you take to accomplish this look with the backsplash flush with the drywall?