They are actually permissable in circumstances similar to John Carmack's:
> California employers can sidestep non-competes in the following instances:
> EXCEPTION 1: If the employee sells business goodwill
> EXCEPTION 2: If the owner sells his or her business interests
> EXCEPTION 3: If the owner sells all operating and goodwill assets
> Upon the business’ dissolution, a member of the company may agree to a non-compete if operating a similar business in the geographic area. Goodwill is the company’s name and brand reputation. Employees with stock options are not considered company owners for purposes of non-competition agreements.
> California employers can sidestep non-competes in the following instances:
> EXCEPTION 1: If the employee sells business goodwill
> EXCEPTION 2: If the owner sells his or her business interests
> EXCEPTION 3: If the owner sells all operating and goodwill assets
> Upon the business’ dissolution, a member of the company may agree to a non-compete if operating a similar business in the geographic area. Goodwill is the company’s name and brand reputation. Employees with stock options are not considered company owners for purposes of non-competition agreements.
https://www.contractscounsel.com/b/non-compete-california