#1 - ignore DadJokes' post. It is wrong on both key points.
As DadJoke's notes - You can contribute to the 401K and 457B for $19K each (2019), plus catch-up if you're old enough. $38K. I'm guessing the confusion is that 401K's and 403B's have a combined limit. 457B is a separate limit.
Minor mistake - Roth 457B's don't work exactly like Roth 401K's, but also Roth 457B's don't work exactly how you'd expect with basic knowledge of the good things about 457B's (penalty-free withdrawal at separation rather than 59.5) and the good things about Roth accounts (tax-free qualified withdrawals).
With a Roth 457B, penalty free withdrawals are indeed available upon separation from employment rather than 59.5 which sounds great for an early retiree. However these withdrawals are not tax-free until 59.5 in a Roth 457B - you pay tax on the earnings portion if you withdraw early. Makes it quite a bit less advantageous than you'd initially think for an early retiree, and it isn't quite the same "Traditional vs. Roth" decision as you'd normally make.
Edit: Misread DadJoke's post. One point is correct, other is not quite right.