The company sets the eligibility requirements, within certain guidelines, at the time the plan is established. Employer can restrict individuals with less than 1 year service, union members, non US citizens, part-time workers, etc., from being eligible for the plan. Contributions to plan can come from voluntary employee salary reduction or from employer, or both. Employer's can establish a vesting schedule, within certain guidelines, for the contribution the company makes to the 401k. Employers are not required nor obligated to make any contribution to the 401k, although employer may have some obligation to contribute if plan is deemed top heavy.
Turnkey plans available.
Investment choices generally range from 8 to 12 options. The current average is 10.6. 401k plans may permit participant directed individual stock transactions and company stock purchase within the plan. This type of plan can permit loans and hardship withdrawals. Participants can start, stop contribution during course of year, as determined by the company.