No, you get more work to fill the other 50%.

But hey, it's not your employer's job to just hand out money. Demand it. Or, if you truly are a 10x dev, just go solo and work 4 hours a week.

Would seem to come down to whether finding ways to do the work twice as fast is part of your responsibilities, rather than simply turning the crank on the job.

A sysadmin is expected to write scripts to image new machines faster, not continue to set up each one painstakingly by hand.