Distributions from a governmental 457(b) are not subject to the 10% additional tax on early distributions. Not at 59½. At all. Ordinary income tax still applies.
A 403(b) generally does carry the 10% additional tax before 59½, subject to exceptions.
Separation from service is what makes 457(b) money available to take. So for a member reaching normal retirement at 53, the 457(b) is reachable and the 403(b) generally is not without cost. In the gap years before 59½, that is the whole difference.
Two exceptions worth knowing:
- Money you rolled into the 457(b) from a 401(k), 403(b), or IRA keeps its original character. It stays subject to the 10% tax.
- Money you roll out of the 457(b) into an IRA becomes subject to IRA rules. The exemption does not travel with it. If you are going to need that money before 59½, a rollover is the decision that takes it away from you.
Source: IRC §72(t)(1) and §4974(c), which leave a governmental 457(b) outside the 10% tax; §72(t)(2) for the 403(b) exceptions; §72(t)(9) for money rolled in; IRS, Exceptions to tax on early distributions.