What are the differences between a Roth 401k and an after-tax 401k, and which one would be more beneficial for my retirement savings?

The main difference between a Roth 401k and an after-tax 401k is how they are taxed. Contributions to a Roth 401k are made with after-tax money, meaning you won't pay taxes on withdrawals in retirement. Contributions to an after-tax 401k are made with pre-tax money, so you'll pay taxes on withdrawals. The choice between the two depends on your current tax situation and future tax expectations. If you expect to be in a higher tax bracket in retirement, a Roth 401k may be more beneficial.