Well, IF you believe this firm, then I think I have now found quite clear information on the IRA/401K exemption question.
Must be savings in the bank on December 31, 2023
ONLY SAVINGS in the bank.
IRAs/401Ks are definitely NOT savings in the bank.
This firm says they are seen as pensions by TR. Accessible income when withdrawn and transferred (unfortunately!).
Episode 7: Pre-2024 savings explained
Of course it's possible other firms and/or TR has a different opinion, but frankly it ain't looking good for that exemption for U.S. retirement accounts.
Another crappy thing about the treatment of U.S. retirement accounts is that unlike non retirement investments, you can't use cost basis to only be liable for the capital gains (if any). Instead you're dealing with the full amount of withdrawals. For example, withdrawal 10K USD from your IRA, transfer that to Thailand, that's 10K USD of Thailand tax accessible income. That 10K might have been from the sale of one stock in your IRA where the capital gain was 1K within the IRA, but still you're in for the full 10K.