The Roth 401(k) is a type of retirement savings plan. It was authorized by the United States Congress under the Internal Revenue Code, section 402A, and represents a unique combination of features of the Roth IRA and a traditional 401(k) plan.oth IRA contribution limits are significantly less than 401(k) contribution limits. For tax-year 2014, individuals may contribute no more than $5,500 to a Roth IRA if under age 50, and $6,500 if age 50 or older.