Cashing out of 401K

hello,
I am a USC on a spousal visa in the UK. Does anyone know what the tax implications will be if I cash out my 401K to my address in the UK. I k now that if I were to do it with a registered address in California (where I am from), I would pay 20% to federal and 10% early cash our penalty (and maybe even % to state tax!). I wanted to see if I cash out while being a resident of UK will save me from some of these tax consequences.

Any help would be greatly appreciated

I don't think it will have an impact.

As a USC you will have the same federal tax issues with the 401k cash out no matter where you live. I don't know your CA residency status or taxes so I can't comment about those. If you have the money sent to you in the UK you will also have to include the income on your UK taxes and take a credit for any US tax you have paid.

I just cashed one of mine out, and only got hit with the standard 20% (iirc) withholding.

I just cashed one of mine out, and only got hit with the standard 20% (iirc) withholding.

US withholding is not final tax.  The US liability for a US citizen is US tax at graduated rates plus a 10% excise tax.

The UK liability would be zero if a UK return is filed electing the use of the treaty.

The UK liability would be zero if a UK return is filed electing the use of the treaty.

Which section of the treaty would be invoked? My initial thought was that the remitted 401k cash would be included on the UK form as income and credit taken for US tax paid. But thinking about it I suppose it would be classed as a lump-sum payment.

So my next question is how is a lump sum defined?