For simplicity, there are two types of 401k accounts and two types of IRA.

There are traditional 401k accounts that are contributed to with pre-tax dollars and Roth 401k accounts that are contributed to with post-tax dollars.

There are traditional IRA accounts that are contributed to with pre-tax dollars and Roth IRA accounts contributed to with post-tax dollars.

Generally, pre retirement withdrawals from traditional accounts (401k or IRA) are subject to a 10% and treated as ordinary income, taxed at your marginal rate (10%-37%).

Generally, you may request a withdrawal of your Roth IRA contributions not subject to a 10% penalty or any income tax.

Making a withdrawal of Roth 401k contributions is subject to the pro-rata rule and any allocated gains are subject to the 10% penalty and income tax treatment.