We know it's the same FM chassis underneath. It's just added the engine from it's platform brother Q50/60. This is not to belittle it, because the FM chassis is excellent and very highly aluminum intensive. Platform sharing saves all kinds of money and cost, and now it's provided the new engine to us thanks to Infiniti. Teh continued existence of the Q50/60, which sells in far higher volume, is what has made it possible to have a new Z. The very low sales of the Z by itself cannot justify a new car, so we have instead what is known in the industry as a "top hat" redesign.
There’s a pretty in-depth story out there that discusses the similarities between these two cars. With the state of Nissan, I can see them not spending much to “redesign” the Z and using a lot of carry over design (Infiniti engine(s), subframes, mounting points, switches, door parts,...)
But I’m still a fan of it bc one day I hope to get one.