No, it is not a new type of plan. Designated Roth contributions are a new type of contribution that can be accepted by new or existing 401k or 403b plans. This feature is permitted under a Code section added by the Economic Growth and Tax Relief Reconciliation Act of 2001 (EGTRRA), effective for years beginning on or after January 1, 2006. If a plan adopts this feature, employees can designate some or all of their elective contributions as designated Roth contributions, (which are included in gross income) rather than traditional, pre-tax elective contributions. So, starting in 2006, elective contributions come in two types: traditional, pre-tax elective contributions (elective contributions are also referred to as elective deferrals) and designated Roth contributions.
A designated Roth contribution is an elective deferral to a section 401k or 403b plan that has been designated irrevocably by an employee as not excludable from the employees gross income and to be deposited into a designated Roth account under the plan. Thus, the contribution is treated by the employer as includible in the employees gross income at the time the employee would have received the amount in cash if the employee had not made the election (hence subject to all applicable wage withholding requirements). Designated Roth contributions are allowed in 401k plans and 403b plans but not in SAR SEPs or SIMPLE IRA plans.
A designated Roth account is a separate account under a section 401k plan or section 403b plan to which designated Roth contributions are made, and for which separate accounting of contributions, gains, and losses is maintained. This separate accounting requirement applies at the time the designated Roth contribution is contributed to the plan and must continue to apply until the designated Roth account is completely distributed.