I've seen posts claiming that if you have a mix of pre-tax and after-tax savings in a 401k, the pre-tax money can be withdrawn up to the threshold of the top of the current 12% tax bracket and after-tax money can be withdrawn in the same year for any additional needed income. This strategy would limit your marginal tax rate to 12% in retirement. Are there any IRS rules that would prevent this?
Some people say that the money has to be withdrawn from the same plan proportionally. If you have $100,000 in pre-tax money and $100,000 in after-tax money all withdraws would have to be 50% pre-tax and 50% after-tax dollars. If that is true, could the money be transferred to separate IRA and Roth IRA accounts to get around that?
Edit: It has been pointed out that I was misunderstanding the meaning of after-tax money. I am interested in any rules governing withdrawals from Traditional and Roth 401k accounts and was unaware of the third category of after-tax money in a Traditional 401k.