What is the best way to transfer 800,000 baht for immigration from Bangkok Bank to Kasikorn Bank while complying with visa requirements?

No change in law......

To be 100% sure, I would go to the immigration and tell them you want to transfere your 800 to another bank. Then ask immigration, what way they prefere your dooing it.

what's the rationale for splitting it up?

You can transfer 2000,000 internal from bank to bank no need to split it up

I am doing just that and the IO said it is ok but maintain the audit trail of the transfer for next extension. The Counter cheque takes a day or two to clear so i can see a problem there. Cash is king in this case i think.

i keep mine in government saving bank. never had any issues and immigration like that’s its with the government bank who provide a letter and 12 months statements for 100 baht. it also gives a small amount of tax free interest.

move 400k, should settle seconds later, check, then do other 400k, no reason to wait if it settles

I've moved mine twice in 2 years as the Bkk bank closed then just recently K bank closed.

Open your new bank account first

Order a statement on the day you're withdrawing the money from your old bank , update your book . Withdraw or transfer the money that day and put it straight into your new bank that day

If you're closing your old bank get the bank book updated to show zero as your bank book as the statement may only show the amount on the previous end of working day .

If you have doubts ask your immigration. I double checked everything again just before i moved my money for the second time in a year .

Why move it ?

Is there a problem ?

I took the 800k in cash and walked into the next bank to deposit it on my new account.

Withdrawal and deposit at the same day so there was no gap.

Canceled BBL account withdraw 800K cash and deposit in Kbank on same day. Keep the bank book is fine.

Move 400k per time

Yes, it's still better to do 400,000 in 2 separate transactions a few days apart. Just do a transfer, don't need to deal with checks.

And make sure you don't close the Bangkok Bank account, because you'll need the bank statements and bank letters from BOTH banks for your next extension to show the money being moved and that you still met last year's requirements. After the upcoming extension, you can then discard the Bangkok Bank account if you'd like.