Some studied show an AI-assisted coding productivity gain of 20%. One is the Google study (*). 
Others show a loss of 20%. One is the METR study (**).
The METR study interestingly reveals a ‘perception gap’: many developers while slowed down, still believe they are more  productive.

The 50% gains estimated or some economists and AI experts, and the x10 gains mentioned by some AI enthusiasts, are still to be captured by any study.

This leaves ...