Former AnandTech editor Gavin Bonshor had reports that the M7 would be manufactured on Intel's 18A node.

https://bontechlabs.com/news/apple-is-reportedly-using-intel...

Given the risks involved in establishing Apple Silicon designs with a new fab, I would expect early M7 parts to be in test production right now.

The fundamental M7 design is already set in stone.

Mark Gurman's Bloomberg article does not mention fabrication partners or processes.