From the supplemental agreement regarding the personal savings plan (exhibit G, available at uaw.org/gm2023)

“The Company shall increase its contribution to an Eligible Employee’s Account from 6.4% to 10% of each such Employee’s Eligible Weekly Earnings with such increase to be implemented by December 31 2023, with contributions made retroactive to October 23, 2023”

It’s a straight up contribution. For every dollar paid in wages, the company also contributes ten cents to the employees 401k. No employee contributions are required.