I just asked Nike. They confirmed it isn't carbon fiber. This is what they told me via their online chat help:
"A 3 / 4 - length injected Pebax spike plate completes the shoe , it provides a stiff platform of propulsion that makes for powerful , reactive strides . The plate's generative design uses an algorithm to identify where zones of stiffness and flexibility are needed and it uses a honeycomb - inspired pattern to achieve this . Zones that demand greater flexibility have larger cutouts that use less material to significantly reduce weight . Six removable spike pins , made of stainless steel , deliver optimal , biting traction . A sharkskin heel pad improves grip , for multi - surface traction , without sacrificing weight ; resisting the traumas of heel - strike to supply you with a reliable , fast and long - lasting race buddy."
They confirmed that there is no carbon fiber plate in the shoe, just a pebax plate.