If someone later becomes a non-resident alien, what's the best option for 401k

[Irish456]

I was a resident alien in NYC have a 401(k) accounts. I have moved to Ireland  and wondering what are my options now that I'm a non-resident alien in the US.

I’ve seen some guidance suggesting a 30% tax, but it’s unclear whether this applies to principal or gains, or both. s I’d like advice on: 1. Should I continue contributing to my 401(k)? If I'm not planning on living the USA again 2. If not, when would be the best time to transfer my existing 401(k)s and liquid it 

[DaveF1006]

No, you should not keep contributing.After you move to Ireland and no longer earn U.S. W-2 wages, you usually can’t contribute to a U.S. 401(k), especially if you have no plans on returning to the US.

As far as transferring or liquidating, there are several options to consider.

1. Roll over to an IRA (The "Wait and See" Strategy) Most expats roll their 401(k) into a Traditional IRA. This keeps the money tax-deferred in the U.S. and gives you more control over investments. There is no immediate tax consequence if you do this and the funds will continue to grow with interest. 
2. If you choose this option, you must eventually take distributions (RMDs) starting at age 73.

If you cash out now, you will face the 30% withholding (unless reduced by the treaty) plus a 10% early withdrawal penalty if you are under age 59½. Ireland will tax this as income. While you can often use the Foreign Tax Credit to avoid paying the full amount to both countries, you will ultimately pay whichever country has the higher rate (usually Ireland).

You may consider the  "Roth Conversion".  Some people convert their Traditional 401(k) to a Roth IRA while their U.S. income is low (perhaps during the "transition year"). You pay tax now, but the money grows and can be withdrawn tax-free later. 

Before you consider this option, you must verify if Ireland recognizes the tax-free status of a Roth IRA (many countries do not).